AU617402B2 - Vaccines for malaria - Google Patents

Description

AU-Al-28135/881 T WORLD INTELLECTUAL-PROPERTY ORGANIZATION SPCT International Bureau INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 C12P 21/00, A61K 39/00 C07K 13/00 (11) International Publication Number: Al (43) I natnal PlicAWh D WO 89/ 02924 5 April 1989 (06.04.89) (21) International Application Number: PCT/US88/03376 (22) International Filing Date: 30 September 1988 (30.09.88) (31) Priority Application Number: (32) Priority Date: 104,735 2 October 1987 (02.10.87) (33) Priority Country: (71) Applicant: PRAXIS BIOLOGICS, INC. [US/US]; 30 Corporate Woods, Rochester, NY 14623 (US).

(72) Inventors- BREY, Robert, III 74 Sagamore Drive, Rochester, NY 14617 MAJARIAN, William, Robert 17 Greenhill Lane, Pittsford, NY 14534 (US).

PILLAI, Subramonia 286 Vollmer Parkway, Rochester, NY 14623 HOCKMEYER, Wayne, T. 9 Brookwood Road, Pittsford, NY 14534 (US).

(74)Agent: MISROCK, Leslie; Pennie Edmonds, 1155 Avenue of the Americas, New York, NY 10036

(US).

(81) Designated States: AT (European patent), AU, BE (European patent), BJ (OAPI patent), BR, CF (OAPI patent), CG (OAPI patent), CH (European patent), CM (OAPI patent), DE (European patent), DK, FR (Eurepean patent), GA (OAPI patent), GD (European patent), HU, IT (European patent), JP, KR, LK, LU (European patent), MG, ML (OAPI patent), MR (OAPI patent), MW, NL (European patent), SD, SE (European patent), SN (OAPI patent), SU, TD (OAPI patent), TG (OAPI patent).

Published With international search report.

Before the expiration of the time limit for amending the claims and to be republished in the event of the receipt of amendments.

UJ.F. JUm 19

AUSTRALIAN

18 APR 1989 PATENT OFFICE (54):Title: VACCINES FOR MALARIA (57) Abstract The present invention is directed to attenuated strains of enteroinvasive bacteria that express a peptide or protein related to an epitope of the malaria parasites of the genus Plasmodium. The bacterial strains of the invention which can multiply in a host without causing significant disease or disorder, and which express a Plasmodium-related peptide that induces a protective immune response against malaria, can be used in live vaccine formulations for malaria. In specific embodiments, a Plasmodium-related peptide can be expressed as a fusion protein, for example, with a bacterial enterotoxin. The invention also relates to methods for expression of malaria antigens or fragments thereof within attenuated enteroinvasive bacteria. In particular embodiments, the invention is directed to the expression by attenuated Salmonella spp. of epitopes of Plasmodium circumsporozoite proteins.

According to a fourth embodiment of this invention, there is WO 89/02924 PCT/US88/03376 1 VACCINES FOR MALARIA 1. FIELD OF THE INVENTION The present invention is directed to attenuated strains of enteroinvasive bacteria that express peptides and proteins related to epitopes of the malaria parasites of the genus Plasmodium. The bacterial strains of the present invention which can multiply in a host without causing significant disease or disorder, and which express Plasmodium-related peptides that induce a protective immune response against malaria, can be used in live vaccine formulations for malaria. Such vaccine formulations can be univalent or multivalent.

In particular, the vaccine vector strains of the present invention comprise attenuated Salmonella bacteria which retain their enteroinvasive properties but lose in large part their virulence properties.

In a preferred embodiment of the invention, a gene or gene fragment encoding all or part of the circumsporozoite malaria antigen can be expressed in Salmonella bacteria that have been attenuated by chromosomal deletion of gene(s) for aromatic compound biosynthesis, for use as a live vaccine for malaria.

2. BACKGROUND OF THE INVENTION 2.1. RECOMBINANT DNA TECHNOLOGY AND GENE EXPRESSION Recombinant DNA technology involves insertion of specific DNA sequences into a DNA vehicle (vector) to form a recombinant DNA molecule which is capable of replication in a host cell. Generally, the inserted DNA sequence is foreign to the recipient DNA vehicle, the inserted DNA sequence and the DNA vector are derived from organisms which do not exchange genetic information in nature, or the inserted DNA sequence may be wholly or partially synthetically made. Several gener 'l methods have been developed which enable construction of recombinant DNA molecules.

WO 89/02924 PCT/US88/03376 2 Regardless of the method used for construction, the recombinant DNA molecule must be compatible with the host cell, capable of autonomous replication in the host cell or stably integrated into one or more of the host cell's chromosomes. The recombinant DNA molecule should preferably also have a marker function which allows the selection of the desired recombinant DNA molecule(s). In addition, if all of the proper replication, transcription, and translation signals are correctly arranged on the recombinant vector, the foreign gene will be properly expressed in, the transformed bacterial cells, in the case of bacterial expression plasmids, or in permissive cell lines or hosts infected with a recombinant virus or carrying a recombinant plasmid having the appropriate origin of replication.

Different genetic signals and processing events control levels of gene expression such as DNA transcription and messenger RNA (mRNA) translation. Transcription of DNA is dependent upon the presence of a promoter, which is a DNA sequence that directs the binding of RNA polymerase and thereby promotes mRNA synthesis. The DNA sequences of eucaryotic promoters differ from those of procaryotic promoters. Furthermore, eucaryotic promoters and accompanying genetic signals may not be recognized in or may not function in a procaryotic system, and furthermore, procaryotic promoters are not recognized and do not function in eucaryotic cells.

Similarly, translation of mRNA in procaryotes depends upon the presence of the proper procaryotic signals, which differ from those of eucaryotes. Efficient translation of mRNA in procaryotes requires a ribosome binding site called the Shine-Dalgarno sequence (Shine, J. and Dalgarno, 1975, Nature 254:34-38) on the mRNA. This sequence is a short nucleotide sequence of mRNA that is located before the start codon, usually AUG, which encodes the amino- WO 89/02924 PCT/US88/03376 3 terminal methionine of the protein. The S/D sequences are complementary to the 3' end of the 16S rRNA (ribosomal RNA), and probably promote binding of mRNA to ribosomes by duplexing with the rRNA to allow correct positioning of the ribosome Successful expression of a cloned gene requires sufficient transcription of DNA, translation of the mRNA and in some instances, post-translational modification of the protein. Expression vectors have been used to express genes under the control of an active promoter in a suitable host, and to increase protein production.

2.2. VACCINATION AGAINST MALARIA A global public health goal is the control and eventual eradication of human malaria. It is estimated that over 500 million people in tropical regions are exposed to malaria annually, and 1.5 to 2 million people die from this disease (Sturchler, 1984, Experientia 40:1357). Efforts to control malaria have historically focussed on control of the mosquito vector and the development of antimalarial drugs. These efforts have met with only limited success. New prophylactic and therapeutic drugs are of limited effectiveness because drug-resistant strains can appear rapidly in endemic areas. Control of the mosquito vector depends largely upon implementation of insecticide-based control programs which, due to cost and other factors, are difficult to maintain in developing nations. Vector resistance to modern insecticides has compounded the problem, and resulted once again in the resurgence of malaria.

Mammalian hosts can be infected by the sporozoite form of the malaria parasite, which is injected by the female Anopheles mosquito during feeding. Sporozoites injected into the bloodstream are carried rapidly to the liver where they invade hepatocytes. Once in hepatocytes, sporozoites i ~Y WO 89/02924 PCT/US88/03376 4 develop into merozoite forms, which are released from hepatocytes and invade erythrocytes. Within the erythrocyte, the parasite asexually reproduces, from rings to schizonts. The mature schizont contains merozoites which, upon rupture of the erythrocyte, can invade other erythrocytes, causing clinical manifestations of the disease.

Some merozoites differentiate into sexual forms, called gametocytes, which are taken up by mosquitoes during a blood meal. After fertilization of gametocytes in the mosquito midgut, developing ookinetes can penetrate the gut wall and encyst. Rupture of such oocysts allows release of sporozoites which migrate to the salivary glands to be injected when the female mosquito takes another blood meal, thus completing the infectious cycle.

Experiments conducted in the 1960s demonstrated that vaccination with X-irradiated sporozoites of P. berqhei protected mice against sporozoite challenge which was lethal in unvaccinated animals (Nussenzweig, et al., 1969, Mil. Med. 134:1176). This observation was later extended to clinical studies in humans, where immunization with X-irradiated sporozoites of P. falciparum or P. vivax protected human volunteers against sporozoite challenge delivered through the bites of infected mosquitoes (Clyde, et al., 1975, Am., J. Trop. Med. Hyg. 24:397; Rieckmann, et al., 1979, Bull. WHO 57:261). This protection was thought to be mediated by antibody. Serum from immunized animals, including humans, formed a precipitate around the surface of live, mature sporozoites. This reaction has been termed the circumsporozoite precipitin (CSP) reaction. These same sera blocked the ability of sporozoites to invade human hepatoma cells in culture (ISI assay) (Hollingdale, et al., 1984, J. Immunol.

132:909). In other studies, a single antigenic determinant localized on the surface of P. berghei sporozoites, termed the circumsporozoite protein, was identified. It was shown I: WO 89/02924 PCT/US88/03376 that a monoclonal antibody reacting with the circumsporozoite (CS) protein of P. berqhei could passively transfer immunity to recipient animals. These animals were protected from sporozoite challenge in a dose-dependent fashion (Potocnjak, et al., 1980, J. Exp. Med. 151:1504).

Evidence also existed that cell-mediated immunity was important (Chen, et al., 1977, J. Immunol. 118:1322; Verhave, et al., 1978, J. Immunol. 121:1031).

The first CS protein gene to be cloned was derived from the H strain of P. knowlesi, a simian parasite (Ozaki et al., 1983, Cell 34:815). The genes encoding the CS proteins of the human malaria parasites P. falciparum (Dame et al., 1984, Science 225:593), P. vivax (McCutchan et al., 1984, Science 230:1381), the simian parasite P. cynomolgi (Enea et al., 1984, Science 225:628), and the rodent parasite P. berqhei (Weber et al., 1987, Exp. Parasitol.

63:295) were also cloned and sequenced. A characteristic feature of the CS genes of each of the parasites is a central region which encodes over one-third of the protein, containing a series of repeated peptide sequences. The primary amino acid sequence, the length of the repeated sequence, and the number of repeats vary with each species of parasite. The repeat region epitopes are characteristic of each species. The gene encoding the CS protein of P.

falciparum specifies a central repeat region of a tetrapeptide (asn-ala-asn-pro) repeated 37 times, interrupted in four locations by the nonidentical tetrapeptide (asn-val-asp-pro). The central repeat region of P. vivax CS protein contains 19 nonapeptides; the central sequence of P. knowlesi contains 12 dodecapeptides, and the repeat region of P. berqhei contains 12 octapeptides. Comparison of sequences from P. knowlesi (H strain) and P. falciparum and P. vivax reveals no sequence homology except for two short amino acid sequences flanking the repeat region, termed Region I and Region II.

'A

WO 89/02924 PCT/US88/03376 6 Efforts to develop an effective anti-sporozoite vaccine for P. falciparum have used peptides derived from the circumsporozoite (CS) repeat region and the two flanking Region I and Region II sequences (Ballou, et al., 1985, Science 228:996). These experiments showed that antibody to the repeat region but not to the conserved sequences recognized authentic CS protein, produced CSP activity, and blocked sporozoite invasion (ISI) in vitro.

A recombinant DNA subunit vaccine composed of 32 P. falciparum tetrapeptide repeats fused to 32 amino acids of the tetracycline resistance gene was produced in E. coli (Young, et al., 1985, Science 228:958). Likewise, a peptide-carrier vaccine composed of three repeats of the peptide asn-ala-asn-pro (NANP) conjugated to tetanus toxoid was developed (Zavala, et al., 1985, Science 228:1436).

In each case, preclinical studies indicated that biologically active (as shown by CSP and ISI) anti-sporozoite antibodies were elicited as a result of immunization (Ballou, et al., 1987, The Lancet 1:1277; Herrington et al., 1987, Nature 328:257). Human safety and immunogenicity studies with both vaccines yielded similar results.

Both vaccine preparations were well tolerated at doses ranging from 10 micrograms to 800 micrograms, and both elicited some anti-CS antibodies in all immunized subjects.

However, high titers were not achieved. In addition, subsequent booster immunizations with the peptide-carrier vaccine did not result in increased antibody titers.

Several individuals from each study were then challenged with live sporozoites in order to test the efficacy of these vaccine preparations. Once again, similar results were achieved with both vaccines; the level of protection (as measured by a delay in the appearance of blood stage parasites) correlated with the anti-CS antibody titers of the challenged individuals, but in each trial, only one L44 U~b-lrr._i~. .ii. i Iiiil .iii-L IWO 89/02924 PCT/US88/03376 7 individual was protected. Parallel studies to evaluate the feasibility of human subunit vaccine development have been examined in the rodent P. berghei malaria model (Egan et al., 1987, Science 236:453).

A recent study has reported that levels of naturally acquired antibodies to the P. falciparum CS protein, as high as those achieved by a subunit sporozoite vaccine (Ballou, et al., 1987, Lancet 1987-1:1277), did not protect against P. falciparum infection during a 98-day interval in a malaria-endemic area.

In different studies, subunit vaccines containing peptides of other P. falciparum antigens have been investigated (Patarroyo, et al., 1987, Nature 629- 632; Cheung, et al., 1986, Proc. Natl. Acad. Sci.

U.S.A. 83:8328-8332; Collins, et al., 1986, Nature 323:259-262). In addition, recombinant vaccinia viruses which express P. falciparum antigens have been described for use (PCT'International Publication Number WO 87/01386, published March 12, 1987).

Perspectives and recent advances in malaria vaccination have been described (Miller, et al., 1984, Phil.

Trans. R. Soc. Lond. B307:99-115; 1985, Vaccines87, Channock et al., eds., Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, pp. 81-106, 117-124).

2.3. BACTERIA OF THE GENUS SALMONELLA Bacteria of the genus Salmonella include over 2,000 serotypes, many of which are capable of causing enteric disease in man and animals. Of the diseases most frequently associated with Salmonell' outbreak, typhoid fever is notable for its severity and high mortality. In humans, typhoid (or enteric) fever results from invasion and dissemination of S. typhi, although other members of the Salmonella are capable of invading and localizing in organ tissues, causing less severe symptoms. In other WO 89/02924 PCT/US88/03376 8 outbreaks of salmonellosis (such as food poisoning), the disease is non-invasive and confined to symptoms of gastroenteritis, and in humans, the disease is not associated with S. typhi. In animals, outbreaks of typhoid fever may be associated with numerous serotypes, S. choleraesuis in swine, S. gallinarum in poultry, and S. dublin and S. typhimurium in cattle (Topley and Wilson's Principles of Bacteriology, Virology, and Immunity, 6th ed., Williams Wilkins Co., Baltimore, MD). The host specificity and severity of the resultant disease varies among the serotypes of Salmonella.

The first instance of an attenuated oral vaccine for typhoid fever in humans was a streptomycin-dependent S.

typhi, but the use of that strain was discontinued.

Germanier (Germanier, R. and Furer, 1975, J. Infect.

Dis. 131:553; Germanier, 1984 in Bacterial Vaccines, Academic Press, New York, pp. 137-165) advocated the use of a galE mutant of S. typhi as an oral vaccine against human typhoid fever.

The S. typhi galE mutant, Ty21a, is capable of eliciting a protective response against the pathogenic parental strain in human volunteers (Levine, et al., 1983, Microbiol. Rev. 47:510; Wahdan, et al., 1982, J Infect. Dis. 145:292). The Ty21a strain also has yielded promising protective results in a field test with 28,000 school children in Alexandria, Egypt (Wahdan, et al., 1982, J. Infect. Dis. 145:292). This vaccine strain is being marketed in Europe as a typhoid fever vaccine.

However, a major disadvantage of this vaccine strain is that it exhibits variable viability due to killing by exogenous galactose. Addition of galactose has two effects on the Ty21a (qglE mutant) strain. Firstly, it results in the accumulation of toxic galactose-l-phosphate, causing reduced viability. Secondly, added galactose is incorporated into the polysaccharide chain of r""i 1

A

SWO 89/02924 PCT/US88/03376 9 lipopolysaccharide, which is necessary for immunogenicity.

These opposing requirements result in variability in viability and in immunogenicity of the vaccine strain.

Recently, Stocker and his coworkers have described a reliable method to achieve attenuation of Salmonella Hoiseth and Stocker, 1981, Nature 291:238; Stocker et al., 1982, Develop. Biol. Standard 53:47; and U.S. Patent No. 4,550,081). In this method, specific deletion mutations affecting the aromatic biosynthetic pathway are introduced by transduction. Specifically, deletions of the gene aroA result in pleiotropic requirements for phenylalanine, tryptophan, tyrosine, and the folic acid precursor, p-aminobenzoic acid, and the enterochelin precursor, dihydroxybenzoic acid. The aromatic amino acids are present in animal tissues, but p-aminobenzoic acid is absent; folic acid which may be present in animal cells is not assimilated by members of the Enterobacteriaceae. In addition, absence of enterochelin results in the requirement for iron in aroA Salmonella strains.

Since the introduction of techniques for the precise attenuation of Salmonella, a number of vaccination studies have been undertaken in animal model systems (Lindberg, A.A. and Robertsson, 1983, Infect. Immun. 41:751; Robertsson, et al., 1983, Infect. Immun. 41:742; Smith, et al., 1984, Am. J, Vet. Res. 45:2231; Smith, et al., 1984, Am. J. Vet. Res. 45:59; Stocker, et al., 1982, Develop. Biol. Standard 53:47).

Using an aroA derivative of S. typhimurium UCD 108-11, SL1479, in the calf model system, Lindberg and coworkers demonstrated invasiveness of SL1479, and showed that calves vaccinated with SL1479 cleared the vaccine organism quickly Sfrom the gut and tissues. Oral vaccination with live SL1479 gave greater protection and cell-mediated immune reactivity against S. typhimurium UCD 108-11 infection than that obtained by intraperitoneal vaccination with heat- WO 89/02924 PCT/US88/03376 killed organisms. In other studies, Smith and colleagues demonstrated protection in calves by vaccination with SL1479, against challenge by the virulent parental strain.

A number of groups have demonstrated expression of heterologous genes in Salmonella. Formal and colleagues transferred the genes for the form I antigen of Shigella sonnei into Salmonella tyhi Ty21a (see Formal, S.B., et al., 1981, Infect. Immun. 34:746; Tramont et al., 1984, J. Inf. Dis. 149:133; and U.S. Patent 4,632,830, by Formal et The form I antigen of Shiqella is associated with immunity elicited by vaccination with live attenuated Shiqella sonnei. Subcutaneous or intraperitoneal injection of living transconjugants protected mice against intraperitoneal challenge by either S. typhi Ty21a or Shigella sonnei. Also, by conjugation experiments, Yamamoto and coworkers (Yamamoto, et al., 1982, J. Bacteriol.

150:1482) introduced an E. coli colonization factor antigen (CFA/I) into Salmonella typhi Ty21a and demonstrated expression of the antigen.

Clements et al. (1983, Infect. Immun. 53:685) tested antibody responses to the B subunit of heat labile toxin derived from enteroinvasive E. coli (EIEC) of human origin (Strain H10407), expressed on a recombinant plasmid in S. typhi Ty21a. Since S. typh has a host range limited to humans and higher primates, immunogenicity was tested in an animal model.. Intraperitoneal injection of the heterologous LT-B in Ty21a resulted in serum antibody responses to LT-B in mice (Clements, J.D. and S. El- Morshidy, 1984, Infect. Immun. 46:564). Subsequently, LT-B producing recombinants were examined in an attenuated Salmonella strain infectious for mice (Clements, et al., 1986, Infect. Immun. 53:685). In this study, the LT-B gene was introduced into an aroA attenuated S. enteriditis serotype dublin strain: SL1438. The parental S. enteriditis dublin strain is virulent in BALB/c mice. After oral ~i~;jlaa; -2 111:11.__~ WO 89/02924 PCT/US88/03376 11 vaccination with the recombinant Salmonella strain, EL23, a significant increase in mucosal anti-LT-B IgA was observed.

The response to LT-B produced by the recombinant organism was less marked than the immune response to purified LT-B injected intraperitoneally or given orally In another study, after introduction of LT-B-encoding plasmids into a aroA deletion mutant of S. typhimurium, SL3261, oral or intraperitoneal vaccination with the recombinant bacteria in mice induced an antibody response to LT-B (Maskell et al., 1987, Microbial Pathogenesis 2:211).

Several other groups have also reported expression of heterologous antigens in attenuated Salmonella. Manning and coworkers (Manning, at al., 1986, Infect. Immun.

53:272) have cloned the gene clusters responsible for lipopolysaccharide synthesis of the 0 antigens of the major biotypes of Vibrio cholerae: Inaba and Ogawa. These gene clusters were expressed on the surface of S. typhi Ty2la.

The K88 fimbrial adhesin antigen of Escherichia coli strains associated with diarrhea of neonatal piglets has been cloned and expressed in S. typhimurium SL3261 (Dougan et al., 1986, Infect. Immun. 52:344). Antibodies against the K88 antigen were obtained from sera of mice receiving either oral or intravenous doses of the recombinant S. typhimurium. In addition, beta-galactosidase has been expressed in S. typhimurium SL3261, and specific antibeta-galactosidase antibodies were elicited by administration of the recombinant bacteria to mice (Brown, et al., 1987, J. Inf. Dis. 155:86), demonstrating that the intracellular beta-galactosidase protein can also provoke an immune response.

3. SUMMARY OF THE INVENTION The present invention is directed to attenuated strains of enteroinvasive bacteria that express peptides rcL1WUi-*~l--- -i-il' I I- WO 89/02924 PCT/US88/03376 12 and proteins related to epitopes of the malaria parasites of the genus Plasmodium. The bacterial strains of the invention which can multiply in a host without causing significant disease or disorder, and which express Plasmodium-related peptides that induce a protective immune response against malaria, can be used in live vaccine formulations for malaria. Such vaccine formulations can be univalent or multivalent.

The expression of Plasmodium epitopes in attenuated enteroinvasive bacteria in the vaccine formulations of the invention provides protective immunity against malaria due to the ability to evoke a cell-mediated immune response in addition to a humoral response. Cell-mediated immunity directed against the Plasmodium epitope results from the invasive properties of the bacteria, which allow presentation of the epitope to the immune system in a manner which can induce cell-mediated immunity.

In particular, the vaccine vector strains of the present invention comprise attenuated Salmonella bacteria which retain their enteroinvasive properties but lose in large part their virulence properties. By obtaining expression of a malarial epitope in attenuated Salmonella, the epitope can be effectively presented to cells important in immune recognition by bacterial invasion, without bacterial persistence or virulence. Thus, effective vaccines against malaria can be achieved. In a preferred embodiment of the invention, a gene or gene fragment encoding all or part of the circumsporozoite malaria antigen can be expressed in Salmonella bacteria that have been attenuated by chromosomal deletion of gene(s) for aromatic compound biosynthesis, for use as a live vaccine for malaria.

The present invention also relates to the methods for expression of the malaria proteins or fragments thereof within attenuated enteroinvasive bacteria. The invention 13 demonstrates the use of plasmid vectors designed for inalaria peptide or protein expression in attenuated enteroinvasive bacteria. In particular embodiments, the invention is directed to methods of obtaining expression of circumsporozoite proteins in attenuated Salmonella spp., and relates to DNA sequences encoding the circumsporozoite proteins of P. falciparum, P. vivax, P. ovale, P. malariae, P. berghei, P. yoelii, P. knowlesi, and P. cynomolgi. The circumsporozoite proteins of the above species of Plasmodium can be expressed in an attenuated Salmonella strain which is enteroinvasive in the animal host for the appropriate malaria parasite.

In another embodiment, the inventicr relates to the expression, by attenuated enteroinvasive bacteria, of malaria proteins as recombinant Sfusion proteins. For example, DNA encoding the circumsporozoite protein or an epitope thereof can be joined to the gene for the B subunit of the heat-labile enterotoxin of E. coli or a portion thereof, in order 15 to achieve enhanced immunogenicity.

In specific embodiments of the present invention described in the examples sections herein, the construction of recombinant plasmid expression vectors which encode epitopes of the circumsporozoite protein of P. berghei, or of P. falciparum, are described. The expression of S 20 recombinant LT-B/CS fusion proteins in attenuated Salmonella strains is I demonstrated. The recombinant Salmonella which express CS peptides are shown to elicit anti-CS antibody production in mice, and to provoke immune responses which protect against malaria infection upon sporozoite challenge.

According to a first embodiment of this invention, there is provided an attenuated enteroinvasive bacterium containing a recombinant DNA sequence which encodes an epitope of a malaria parasite which sequence can be expressed by the bacterium such that an immune response against the malarial parasite is generated by a host inoculated with the bacterium.

I 30 According to a second embodiment of this invention, there is provided a vaccine formulation comprising a bacterium of the first embodiment in which the epitope is characteristic of the sprorzoite stage of the malaria parasite, and in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

According to a third embodiment of this invention, there is provided a vaccine formulation comprising a bacterium of the first embodiment in which the epitope is characteristic of the erythrocytic stage of the malaria parasite, and in which the bacterium is infectious without R causing significant disease in a host to be vaccinated.

LMM/606Z r L^ M lr 13A According to a fourth embodiment of this invention, there is provided a vaccine formulation comprising a bacterium of the first embodiment in which the epitope is characteristic of the exoerythrocytic stage of the malaria parasite, and in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

According to a fifth embodiment of this invention, there is provided a vaccine formulation comprising a bacterium of the first embodiment, in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

According to a sixth embodiment of this invention, there is provided a multivalent vaccine formulation comprising a bacterium of the first S: embodiment and a bacterium capable of expression of a second heterologous S epitope, which bacteria are infectious without causing significant disease in a host to be vaccinated.

15 According to a seventh embodiment of this invention, there is provided a method for expressing an epitope of a malaria parasite, comprising: a) constructing an attenuated enteroinvasive bacterium containing S a recombinant DNA sequence which encodes an epitope of a malaria parasite, 20 which sequence can be expressed by the bacterium; and b) allowing the bacterium to grow under conditions which induce the expression of the encoded epitope.

SAccording to an eighth embodiment of this invention, there is provided an attenuated bacterium of the genus Salmonella having an aroA or galE mutation and containing a recombinant DNA sequence which encodes an epitope of a circumsporozoite protein antigen of a plasmodial malarial parasite which sequence can be expressed such that an immune response against the malarial parasite is generated in a host inoculated with the bacterium.

3.1. DEFINITIONS CS circumsporozoite CSP reaction circumsporozoite precipitin

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LMM/606Z s ,A WO 89/02924 PCT/US88/03376 14 reaction DNase deoxyribonuclease DTT dithiothreitol EIEC enteroinvasive E. coli ELISA enzyme-linked immunoabsorbent assay i.p. intraperitoneally IPTG isopropylthio-beta-D-galactoside ISI inhibition of sporozoite invasion kD kiloDalton KLH keyhole limpet hemocyanin LB Luria broth LT-B the B subunit of the heat-labile enterotoxin of E. coli mAb monoclonal antibody PAGE polyacrylamide gel electrophoresis PBS phosphate-buffered saline PL leftward promoter of bacteriophage lambda PR rightward promoter of bacteriophage lambda.

RNase ribonuclease S/D Shine-Dalgarno SDS sodium dodecyl sulfate 4. BRIEF DESCRIPTION OF THE FIGURES Figure 1. Nucleotide sequence of the P. berghei circumsporozoite gene. Sequence data is according to Weber et al., 1987, Experimental Parasitol. 63:295. The gene sequence comprises approximately 75% of the sequence of the mature gene and includes the sequence of linkers used in the original cloning of the gene in lambda gtll. Major restriction enzyme sites are indicated. The P. berghei specific DNA starts with the CGA codon encompassing the first NruI site.

WO 89/02924 PCT/US88/03376 Figure 2. Nucleotide and amino acid sequence of the P. berghei circumsporozoite protein. The repeated immunodominant epitopes are shown in brackets, and consist of a consensus octapeptide repeat, DPAPPNAN, and a second less frequent octapeptide repeat, DPPPPNPN. Regions I and II are underlined. Repeated dipeptide units are also shown in brackets.

Figure 3. Gene and protein sequence of LT-B derived from Escherichia coli H10407. The DNA sequence and protein sequence of the coding region of the LT-B gene is included within a 588 base pair EcoRI-HindIII restriction fragment.

A short Shine-Dalgarno site is within seven base pairs of the initiating codon ATG, and is underlined. The protein sequence of LT-B includes a 21 amino acid signal sequence (shown in brackets) which is processed in the mature form, beginning with alanine. The Clal, XmaI, and Spel restriction enzyme recognition sites in LT-B which were useful in constructing fusion protein molecules are shown.

Figure 4. Is a diagrammatic representation of the construction of plasmid pPX100, a vector which expresses LT-B under the control of the lac operon. Plasmid pJC217 was digested with EcoRI and religated to delete 180 base pairs of DNA including extraneous restriction sites of the polylinker, to yield plasmid pPX100.

Figure 5. Is a diagrammatic representation of the construction of plasmid vectors which express LT-B/CS fusion proteins under .the control of the lac operon. The DNA sequence of the P. berghei CS gene shown in Figure 1 encompasses a large 1.1 kilobase pair NruI and a smaller 670 base pair XmnI fragment which were both inserted into the filled out Clal site of pPX100, to yield plasmids pPX1515 and pPX1520.

Figure 6. Is a diagrammatic representation of portions of vectors constructed to express LT-B/CS fusion proteins regulated by the translation initiation signals of WO 89/02924 PCT/US88/03376 16 LT-B. The 670 base pair XmnI CS fragment described in Figure 5 was inserted at the Clal site (pPXl515), at the Xmal (pPX1523) or the SpeI (pPX1525) site of the LT-B sequence. The resulting vectors express LT-B/CS fusion proteins using the translation initiation signals of the LT-B protein. Relative positions of translation stop codons within-the sequence derived from the LT-B insert are indicated by asterisks.

Figure 7. Is a diagrammatic representation of the construction of tac promoter-driven LT-B/CS fusion proteins. The EcoRI-HindIII restriction enzyme fragments containing the LT-B/CS fusion sequence, from either pPX1515, pPX1523, or pPX1525, were isolated and ligated into the EcoRI-HindIII sites of pKK223. The resulting plasmids can express the LT-B/CS fusion proteins under the control of the tac promoter. The construction of pPX1528 is shown as an example.

Figure 8. Is a diagrammatic representation of the construction of PL promoter-driven LT-B/CS fusion proteins.

The EcoRI-HindIII fragments, containing the LT-B/CS fusion sequences, isolated from either pPX1515, pPX1523, or pPX1525, were "filled out" with Klenow enzyme and ligated into the HpaI site of plasmid pPL lambda. The resulting plasmids can express LT-B/CS fusion proteins under the control of the PL promoter. The construction of pPX1601 is shown as an example.

Figure 9. Is a diagrammatic representation of the construction of PL promoter-driven expression vector pPX1600. An oligonucleotide encoding several restriction enzyme sites, a consensus Shine-Dalgarno sequence, a translation initiation codon, and translation termination codons in all three reading frames was synthesized and ligated into the HpaI site of pPL lambda to yield pPX1600.

pPX1600 can be used to conveniently insert and express heterologous sequences under the control of the P 35 WO 89/02924 PCT/US88/03376 17 promoter.

Figure 10. Is a diagrammatic representation of the construction of a plasmid vector containing the P. berqhei CS gene driven by the PL promoter. The 670 base pair XmnI fragment of the P. berqhei CS gene was isolated and ligated directly into the filled out NcoI site of plasmid pPX1600 to yield pPX1529. Plasmid pPX1529 can express the P.

berqhei CS gene sequence under the control of the PL promoter.

Figure 11. Is a diagrammatic representation of the construction of plasmid vectors which encode immunodominant epitopes of P. falciparum or P. berqhei CS protein, driven by the PL promoter. By ligating polymerized oligonucleotides encoding CS epitopes (obtained as described in Section 7.7, infra), into the filled out NcoI site of pPX1600, various plasmids containing the oligonucleotides as inserts were isolated. For purposes of demonstration, the insertion of an oligonucleotide encoding four repeats of the P. falciparum CS epitope is shown. A monomeric insert results from the insertion of one copy of the oligonucleotide into the NcoI site. The resulting plasmids can express CS epitopes under the control of the PL promoter.

Figure 12. Is a diagrammatic representation of the construction of a plasmid vector which can express the full length P. falciparum CS protein gene under the control of the PL promoter. The StuI-RsaI DNA fragment of the P.

falciparum CS protein gene was ligated into the StuI site of plasmid pPX1600 to yield plasmid pPX1534, which expresses the full length CS gene (lacking only a region encoding the putative 16 amino acid signal sequence) from the PL promoter.

Figure 13. Expression of LT-B/CS fusion protein in S. dublin SL1438 with increasing strength of promoter. The gene encoding a fusion protein in which 30 amino acids of WO 89/02924 PCT/US88/03376 18 mature LT-B is fused in-frame with 223 amino acids of the P. berqhei CS protein, was linked, using the same translation initiation signals, to different promoters. Proteins were separated by SDS-polyacrylamide gel electrophoresis and transferred to nitrocellulose for detection of CS protein with anti-CS mAb 3.28, in a western blotting procedure. The following vectors were expressed in S. dublin SL1438: Lane 1, vector pUC8; Lane 2, pPX1515 (lac promoter); Lane 3, pPX1528 (tac promoter); Lane 4, pPX1601 (PL promoter). The arrow indicates the position of the CS protein.

Figure 14. Expression in Salmonella dublin of betagalactosidase/CS or LT-B/CS fusion proteins driven by the lac promoter. Proteins synthesized in S. dublin SL1438 were separated by SDS-polyacrylamide gel electrophoresis, and transferred to nitrocellulose for detection of the CSspecific epitope with anti-CS mAb 3.28, in a western blotting procedure. The following vectors were expressed in S. dublin SL1438: Lane 1, vector pUC8; Lane 2, pPX1512; Lane 3, pPX1514; Lane 4, pPX1515; Lane 5, pPX1520; Lane 6, pPX1522. (For a description of each of the plasmid constructions, see Sections 7.1-7.9, infra).

Figure 15. Expression of LT-B/CS P. berghei fusion protein, under the control of various promoters, in S.

typhimurium, S. dublin, and S. typhi. aroA mutants of the indicated Salmonella strains were grown to midlog phase in Luria broth containing 50 micrograms per ml of ampicillin.

Total protein samples were subjected to electrophoresis in SDS-PAGE and western blotting as described in Sections 6.9 and 6.10. The arrows on the left indicate protein molecular weights expressed in kiloDaltons; the arrow on i the right indicates the position of the LT-B/CS fusion protein.

Figure 16. Isoelectric focussing of proteins obtained from E. coli and Salmonella strains which express the P.

WO 89/02924 PCT/US88/03376 19 falciparum repeat epitope fused to the first thirty amino acids of LT-B. Sonicated extracts of the indicated strains, containing approximately 50 micrograms of protein, were subjected to isoelectric focussing in a vertical gel apparatus as described in Section 6.10. Ty523 is an S.

typhi aroA mutant; SL3261 is an S. typhimurium aroA mutant, and SL1438 is an S. dublin aroA mutant. E. coli strain JM103 containing plasmid pPX1532 was induced with 1 mM IPTG; as a control, the same strain without IPTG induction is shown. The principal immunoreactive species are indicated by arrows at the right.

Figure 17. Anti-CS protein serum antibody response to recombinant Salmonella dublin SL1438 expressing an LT-B/CS fusion protein, or LT-B. C57bl/6 mice received a primary vaccinating dose of 10 S. dublin carrying the indicated plasmids by the intraperitoneal route. Mice were boosted i.p. at week 4 with 108 organisms of the same strain as the primary dose. Anti-CS protein antibody response was measured in an ELISA with a 1:160 dilution of serum taken at week four. Data are expressed as OD (optical density) values measured at 410 nm. pPX1527 encodes LT-B driven by the tac promoter; pPX1528 encodes an LT-B/CS fusion protein driven by the tac promoter; and pPX1601 encodes an LT-B/CS fusion protein driven by the PL promoter.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to attenuated strains of enteroinvasive bacteria that express peptides and proteins related to epitopes of the malaria parasites of the genus Plasmodium. The bacterial strains of the present invention which can multiply in a host without causing significant disease or disorder, and which express Plasmodium-related peptides that induce a protective immune response against malaria, can be used in live vaccine WO 89/02924 PCT/US88/03376 formulations for malaria. Such vaccine formulations can be univalent or multivalent.

The expression of Plasmodium epitopes in the vaccine formulations of the present invention provides protective immunity against malaria due to the ability of such vaccine formulations to evoke a cell-mediated immune response in addition to a humoral response. Cell-mediated immunity directed against the Plasmodium epitope results from the invasive properties of the bacteria, which allow presentation of the epitope to the host immune system in a manner which can induce cell-mediated immunity.

In particular, the vaccine vector strains of the present invention comprise attenuated Salmonella bacteria which retain their enteroinvasive properties but lose in large part their virulence properties. Bacteria of the genus Salmonella can invade intestinal epithelial cells and establish systemic infections by invading the reticuloendothelial system of the host animal. By causing attenuation of virulent bactesia, invasive properties of the bacteria are retained but their virulence properties are lost.

In a preferred embodiment of the invention, a gene or gene fragment encoding all or part of the circumsporozoite malaria antigen can be expressed in Salmonella bacteria that have been attenuated by chromosomal deletion of gene(s) for aromatic compound biosynthesis, for use as a live vaccine for malaria.

By obtaining expression of the circumsporozoite proteins of the malarial sporozoites in attenuated Salmonella, sporozoite antigens can be effectively delivered to the specific cells important in immune recognition by bacterial invasion without bacterial persistence or virulence. In this fashion, effective vaccines against malaria sporozoites can be achieved.

The present invention also relates to the methods for WO 89/02924 PCT/US88/03376 21 expression of the malaria proteins or fragments thereof within attenuated enteroinvasive bacteria. The invention also demonstrates the use of plasmid vectors designed for malaria peptide or protein expression in attenuated entero-.

invasive bacteria. In particular embodiments, this invention is directed to methods of obtaining expression of circumsporozoite proteins in attenuated Salmonella spp. and relates to-DNA sequences encoding the circumsporozoite proteins of P. falciparum, P. vivax, P. ovale, P. malariae, P. berghei, P. yoelii, P. knowlesi, and P. cynomolgi. The circumsporozoite proteins of the above species of Plasmodium can be expressed in an attenuated Salmonella strain which is enteroinvasive in the animal host for the appropriate malaria parasite. In a specific embodiment, the invention also relates to the expression of the P. falciparum circumsporozoite protein or immunogenic portion thereof in attenuated S. typhi containing aroA chromosomal deletion mutation(s), for use as a live vaccine against the most serious form of human malaria. In another specific embodiment, the invention relates to the expression of P.

berqhei circumsporozoite protein in attenuated Salmonella which are enteroinvasive for mice, as a model system to study the efficacy of the live vaccines of the present invention for human malaria, In another embodiment, the invention relates to the expression of malaria proteins as recombinant fusion proteins. Such fusion proteins can exhibit increased immunogenicity of malaria epitopes. In a particular embodiment, by obtaining fusion circumsporozoite proteins using recombinant DNA technology, the immunogenicity of the circumsporozoite protein can be modified. In such an embodiment, DNA encoding the circumsporozoite protein or an epitope thereof can be joined to the gene for the B-subunit of the labile enterotoxin of E. coli or a portion thereof, in order to achieve modified immunogenicity.

WO 89/02924 PCT/US88/03376 22 Fusion LT-B/circumsporozoite protein immunogens expressed in Salmonella spp. can supply additional T cell helper functions. In this embodiment, coupling of an epitope of the circumsporozoite protein to LT-B also directs the recombinant DNA-derived fusion protein to the periplasmic space of the invasive Salmonella, and aids in antigen presentation.

The method of the invention may be divided into the following stages solely for the purpose of description: isolation of a gene, or gene fragment, encoding an epitope of a malaria parasite; insertion of the gene or gene fragment into an expression vector; transfer to and expression of the gene or gene fragment in an attenuated enteroinvasive bacteria; determination of immunopotency of the malaria epitope expressed by the recombinant enteroinvasive bacteria; and formulation of a vaccine.

In specific embodiments of the present invention described in the examples sections herein, we describe the construction of recombinant plasmid expression vectors encoding epitopes of the circumsporozoite protein of P.

berghei, or of P. falciparum. We further describe the expression of recombinant LT-B/CS fusion proteins in attenuated Salmonella strains. The recombinant Salmonella which express CS peptides are shown to elicit anti-CS antibody production in mice, and to provoke immune responses which protect against malaria infection upon sporozoite challenge.

5.1. ISOLATION OF GENE OR GENE FRAGMENTS ENCODING PLASMODIUM EPITOPES Any DNA sequence which encodes a Plasmodium epitope, which when expressed as a fusion or nonfusion protein in an attenuated enteroinvasive bacteria, produces protective immunity against malaria, can be isolated for use in the vaccine formulations of the present invention. The species of Plasmodium which can serve as DNA sources include but SWO 89/02924 PCT/US88/03376 23 are not limited to the human malaria parasites P. falciparum, P. vivax, P. ovale, P. malariae, and the animal malaria parasites P. berqhei, P. yoelii, P. knowlesi, and P. cynomolgi.

There are numerous genes which encode a Plasmodium antigen that can serve as a source of the DNA sequence to be isolated and expressed in attenuated enteroinvasive bacteria according to the present invention. The antigens, or fragments thereof, which can be expressed by recombinant bacteria in the vaccine formulations of the invention are antigens which are expressed by the malaria parasite at any of the various stages in its life cycle, such as the sporozoite, exoerythrocytic (development in hepatic parenchymal cells), asexual erythrocytic, or sexual gametes, zygotes, ookinetes) stages. The antigen can be expressed by the malaria parasite itself or by an infected cell. The Pla'Todium antigens which may be used include but are not limited to those described in the following publications, incorporated by reference herein: 1985, Lerner, et al., eds., Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, pp. 1-57 Vaccines86, 1986, Brown, et al., eds., Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, pp. 135-179 Vaccines87, 1987, Channock et al., eds., Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, pp. 81-106, 117-124 Kemp, et al., 1983, Proc. Natl. Acad. Sci. U.S.A.

80:3787 Anders, et al., 1984, Mol. Biol. Med. 2(3):177-191 Miller, et al., 1984, J. Immunol. 132(1):438-442 Carter, et al., Nov. 13, 1984, Philos. Trans. R. Soc.

Lond. (Biol.) 307(1131):201-213 Holder, A.A. and Freeman, 1981, Nature 294:361 Leech, et al., 1984, J. Exp. Med. 159:1567 WO 89/02924 PCT/US88/03376 24 Rener, et al., 1983, J. Exp. Med. 158:971 Dame, et al., 1984, Science 225:593 Arnot, et al., 1985, Science 230:815 Coppel, et al., 1983, Nature 306:751 Coppel, et al., 1984, Nature 310:789 Holder, et al., 1985, Nature 317:270 Ardeshir, et al., 1987, EMBO J. 6:493 Ravetch, et al., 1985, Science 227:1593 Stahl, et al., 1985, Proc. Natl. Acad. Sci. U.S.A.

82:543 Langsley, et al., 1985, Nuci. Acids Res. 11:4191 Coppel, et al., 1985, Proc. Natl. Acad. Sci. U.S.A.

82:5121 Howard, et al., 1987, J. Cell Biol. 104:1269 Buranakitjaroen, P. and Newbold, 1987, Mol. Biochem.

Parasitol. 2: Schofield, et al., 1986, Hal. Biochem. Parasitol.

18: 183 Aley, et al., 1984, J. Exp. Med. 160:1585 Knowles, and Davidson, 1984, Am. J. Trop. Med.

Hyg. 33:789 Kilejian', 1979, Proc. Natl. Acad. Sci. U.S.A. 76:4650 Leech, et al., 1984, J. Cell. Biol. 98:1256 Hadley, et al., 1986, Ann. Rev. Microbial. 40t451 Camus, D. and Hadley, 1985, Science 230:553 Vermeulen, et al., 1985, J. Exp. Med. 162:1460.

Vermeulen, et al., 1986, Hal. Biochem. Parasitol.

155 Kumnar, N. and Carter, 1984, Mol. Biochem. Parasiti;'.

13:333 Patarroyo, et al., 1987, Nature 328:629-632 Miller, et al., 1984, Phil. Trans. R. Soc. Lond.

B307: 99-115.

As particular examples, such antigens include the circumsporozoite antigen; the P. falciparum blood-stage WO 89/02924 PCT/US88/03376 ring-infected erythrocyte surface antigen (RESA), S antigen, Falciparum interspersed repeat antigen (FIRA), glycophorin binding protein (GBP), Pf 195 kD antigen, circumsporozoite protein-related antigen (CRA), Pf 155 antigen, Pf 75 kD antigen, Pf EMP 2 antigen, and Pf knobassociated antigens; P. falciparum sexual stage antigens of 260,000, 59,000 and 53,000 molecular weight, antigens of 230,000, 48,000, and 45,000 molecular weight, etc.

In a particular embodiment, a Plasmodium peptide can be expressed as a fusion protein with a secreted protein sequence of a bacteria, so that the recombinant fusion protein is directed to the periplasmic space of the bacteria, thus aiding presentation to the immune system and enhancing immunogenicity.

Although extracellular localization of the Plasmodium epitope expressed by the recombinant enteroinvasive bacteria is preferred, extracellular localization is not required, since intracellular localization can also evoke an effective immune response. When beta-galactosidase, an intracellular protein, was expressed in S. typhimurium SL3261, specific anti-beta-galactosidase antibodies were elicited by administration of the recombinant bacteria to ,mice (Brown, et al., 1987, J. Inf. Disc. 155:86).

In a preferred embodiment, the malaria epitope to be expressed is an epitope of the circumsporozoite (CS) protein of a species of Plasmodium. Analogous CS proteins have been identified on the surfaces of sporozoites of all serotypes of Plasmodium. Circumsporozoite protein antigens expressed in attenuated Salmonella spp. can be used as live vaccines directed against sporozoites, the invasive form of malaria parasites transmitted by the female Anopheles mosquito. The genes which encode a CS epitope and which may be isolated for use include but are not limited to those Plasmodium species listed supra. In particular, those genes encoding the CS proteins of the human malaria WO 89/02924 PCT/US88/03376 26 parasites P. falciparum, P. vivax, the simian parasites P.

cynomolgi and P. knowlesi, and the rodent parasite P.

berghei can be used; these genes have been cloned and sequenced, as reported in the following publications, which are incorporated by reference herein: Dame, et al., 1984, Science 225:593: Arnot, et al., 1985, Science 230:815; Weber et al., 1987, Exp. Parasitol. 63:295; Enea, et al., 1984, Science 225:628; Enea, et al., 1984, Proc. Natl. Acad. Sci. U.S.A. 81:7520; Godson, et al., 1983, Nature 305:29; and McCutchan, et al., 1985, Science 230:1381. A characteristic feature of the CS genes of each of the parasites is a central region which comprises over one third of the protein and contains a large series of repeated peptide sequences (Dame, et al., 1984, Science 225:593; Ozaki, et al., 1983, Cell 34:815). The primary amino acid sequence, the length of the repeating sequence, and the number of repeats varies with each species of parasite. As examples, the gene encoding the CS protein of P. falciparum specifies a central repeat region of a tetrapeptide (asn-ala-asn-pro) repeated thirty-seven times, interrupted in four locations by a variant tetrapeptide (asn-val-asp-pro). The central repeat region of P. vivax contains nineteen nonapeptides; the central sequence of P. knowlesi contains eight dodecapeptides, and the repeat region of P. berqhei contains twelve octapeptides. Comparison of sequences from P. knowlesi (H strain) and P. falciparum and P. vivax revealed no sequence homology, except for two short amino acid sequences flanking the repeat region, termed Region I and Region II. The repeat regions appear to be highly conserved within the human malaria parasites P. falciparum Sand P. yivax (Weber, J.L. and Hockmeyer, 1984, Mol.

Biochem. Parasitol. 15:305; Zavala, et al., 1985, J.

Immunol. 135:2750), though intra-species variation has been observed in P. knowlesi and P. cymolgi. The repeat

I

WO 89/02924 PCT/US88/03376 27 region also appears to be immunodominant (Dame, et al., 1984, Science 225:593; Hockmeyer, W.T. and Dame, J.B., 1985, in Immunobiology of Proteins and Peptides III, Atassi, ed., Plenum Press, New York, pp. 233-246; Zavala, et al., 1983, J. Exp. Med. 157:1947; Zavala, et al., 1985, Science 228:1436). In preferred embodiments of the invention, DNA sequences containing the repeat region, Region I, or Region II, can be isolated for use in the vaccine formulations of the present invention.

For example, in one embodiment, the peptide asn-ala-asnpro, related to the P. falciparum CS repeat region, can be expressed by the recombinant bacteria of the invention. In another embodiment, the peptide asp-pro-ala-pro-pro-asnala-asn, representing the P. berqhei CS protein repeat region, can be expressed.

The Plasmodium CS peptides to be expressed in recombinant enteroinvasive bacteria according to the present invention, whether produced by recombinant DNA methods, chemical synthesis, or purification techniques, include but are not limited to all or part of the amino acid sequences of Plasmodium-specific antigens, including altered sequences in which functionally equivalent amino acid residues are substituted for residues within the sequence resulting in a silent change. For example, one or more amino acid residues within the sequence can be substituted by another amino acid of a similar polarity which acts as a functional equivalent, resulting in a silent alteration. Substitutes for an amino acid within the sequence may be selected from other members of the class to which the amino acid belongs. For example, the nonpolar (hydrophobic) amino acids include alanine, leucine, isoleucine, valine, proline, phenylalanine, tryptophan, and methionine. The polar neutral amino acids include glycine, serine, threonine, cysteine, tyrosine, asparagine, and glutamine. The positively charged (basic) amino acids WO 89/02924 PCT/US88/03376 28 include arginine, lysine, and histidine. The negatively charged (acidic) amino acids include aspartic and glutamic acid.

A DNA sequence encoding a malarial epitope which is a hapten, a molecule that is antigenic in that it can react selectively with cognate antibodies, but not immunogenic in that it cannot elicit an immune response, can be isolated for use in the vaccine formulations of the present invention, since it is envisioned that, in particular embodiments, presentation by the enteroinvasive attenuated bacteria of the invention can confer immunogenicity to the hapten expressed by the bacteria. As particular examples, expression of a malarial hapten as a fusion protein with an immunogenic peptide, derived from E. coli enterotoxin subunit B can confer immunogenicity.

5.2. CONSTRUCTION OF EXPRESSION VECTORS CONTAINING SEQUENCES WHICH ENCODE A PLASMODIUM EPITOPE In this aspect of the invention, the desired DNA sequence encoding the malarial epitope is inserted, using recombinant DNA methodology (see Maniatis, 1982, Molecular Cloning, A Laboratory Manual, Cold .Spring Harbor Laboratory, Cold Spring Harbor, New York), into an expression vector so that it can be expressed under the control of an active promoter in the host attenuated enteroinvasive bacteria. The DNA sequence encoding the Plasmodium epitope can be obtained from any of numerous sources such as cloned malarial DNA, genomic malarial DNA, cDNA of malarial RNA, or chemically synthesized DNA.

In order to generate Plasmodium DNA fragments, the Plasmodium DNA may be cleaved at specific sites using Svarious restriction enzymes. Alternatively, one may use DNaseI in the presence of manganese, or mung bean nuclease (McCutchan et al., 1984, Science 225:626), to fragment the DNA, or the DNA can be physically sheared, as for example, by sonication. The linear DNA fragments can then be i;' WO 89/02924 PCT/US88/03376 29 separated according to size by standard techniques, including, but not limited to, agarose and polyacrylamide gel electrophoresis and column chromatography.

Any restriction enzyme or combination of restriction enzymes may be used to generate Plasmodium DNA fragment(s) containing the desired epitope(s), provided the enzymes do not destroy the immunopotency of the encoded product.

Consequently, many restriction enzyme combinations may be used to generate DNA fragments which, when inserted into a appropriate vector, are capable of directing the production of the peptide containing the Plasmodium epitope.

Once the DNA fragments are generated, identification of the specific DNA fragment containing the desired malaria sequence may be accomplished in a number of ways. For example, if a small amount of the desired DNA sequence or a homologous sequence is previously available, it can be used as a labeled probe nick translated) to detect the DNA fragment containing the desired sequence, by nucleic acid hybridization. Alternatively, if the sequence of the derived gene or gene fragment is known, isolated fragments or portions thereof can be sequenced by methods known in the art, and identified by a comparison of the derived sequence to that of the known DNA or protein sequence.

Alternatively, the desired fragment can be identified by techniques including but not limited to mRNA selection, making cDNA to the identified mRNA, chemically synthesizing the gene sequence (provided the sequence is known), or selection on the basis of expression of the encoded protein by antibody binding) after "shotgun cloning" of various DNA fragments into an expression system.

Once identified and isolated, the Plasmodium DNA fragment containing the sequence(s) of interest is then inserted into a vector which is capable of replication and expression in the host enteroinvasive bacteria. The Plasmodium DNA may be inserted into the bacterial chromoso-

'A

I~

W0189/02924 PCT/US88/03376 mal DNA. Alternatively, in a preferred embodiment, the Plasmodium DNA is inserted into a cloning vector which can exist episomally, a plasmid or bacteriophage, which is then used to transform or infect appropriate host bacterial cells, where the Plasmodium DNA is replicated and S expressed.

If the complementary restriction sites used to fragment the Plasmodium DNA are not present in the cloning vector, the ends of the DNA molecules may be modified (for example, see Section 6, infra).. Such modifications include producing blunt ends by digesting back single-stranded DNA termini or by filling the single-stranded termini so that the ends can be blunt-end ligated. Alternatively, any site desired may be produced by ligating nucleotide sequences (linkers) onto the DNA termini; these ligated linkers may comprise specific chemically synthesized oligonucleotides encoding restriction site recognition sequences. According to other methods, the cleaved vector and the Plasmodium DNA fragment may be modified by homopolymeric tailing.

The transformation of attenuated enteroinvasive bacteria with the recombinant DNA molecules that incorporate the Plasmodium DNA enables generation of multiple copies of the Plasmodium sequence. A variety of vector systems may be utilized for expression within the bacterial host, including but not limited to plasmids such as pUC plasmids and derivatives, PBR322 plasmid and derivatives, bacteriophage such as lambda and its derivatives, and cosmids. In a specific embodiment, plasmid cloning vectors which can be used include derivatives of ColE1 type replicons (for additional information, see Oka et al., 1979, Mol. Gen. Genet. 172:151-159). The ColEl plasmids are stably maintained in E. coli and Salmonella tvphimurium strains as monomeric molecules with a copy number of about 15-20 copies per cell. Various regulatory expression elements can be used, which are any of a number of suitable i~ WO 89/02924 PCT/US88/03376 31 transcription and translation elements that are active in the attenuated enteroinvasive bacteria of the invention.

For instance, promoters which may be used to direct the expression of the Plasmodium DNA sequence include but are not limited to the lactose operon promoter of E. coli, the hybrid trp-lac UV-5 promoter (tac) (DeBoer, et al., 1982, in Promoter Structure and Function, Rodriguez, R.L.

and Chamberlain, eds., Praeger Publishing, New York), the leftward (PL) and the rightward (PR) promoters of bacteriophage lambda, the bacteriophage T7 promoter, the trp operon promoter, the Ipp promoter (the E. coli lipoprotein gene promoter; Nakamura, K. and Inouye, I., 1979, Cell 18:1109-1117), etc. Other promoters produced by recombinant DNA or synthetic techniques may also be used to provide for transcription of the inserted sequences.

Specific initiation signals are also required for efficient translation of inserted protein coding sequences.

These signals include the ATG initiation codon and adjacent sequences. In cases where the entire Plasmodium gene including its own initiation codon and adjacent sequences are inserted into the appropriate expression vectors, no additional translational control signals may be needed.

However, in cases where only a portion of the gene sequence is inserted, exogenous translational control signals, including the ATG initiation codon, must be provided. The initiation codon must furthermore be in phase with the reading frame of the protein coding sequences to ensure translation of the entire insert. These exogenous translational control signals and initiation codons can be of a variety of origins, both natural and synthetic.

Any of the methods previously described for the insertion of DNA fragments into a vector may be used to construct expression vectors containing a chimeric gene consisting of appropriate transcriptional/translational control signals and the protein coding sequences. These i ?A WO 89/02924 PCT/US88/03376 32 methods may include in vitro recombinant DNA and synthetic techniques and in vivo recombinations (genetic recombination).

For reviews on maximizing gene expression, see Roberts and Lauer, 1979, Meth. Enzymol. 68:473; and Reznikoff, W.

S and Gold, 1986, Maximizing Gene Expression, P±enum Press, New York.

The Plasmodium peptide or protein can be expressed as a fusion or nonfusion recombinant protein. E. coli and other bacteria contain an active proteolytic system which appears to selectively destroy "abnormal" or foreign proteins (Bukhari, A. and Zipser, 1973, Nature 243:238). In order to protect eucaryotic proteins expressed in bacteria from proteolytic degradation, one strategy which can be used is to construct hybrid genes in which the foreign sequence is ligated in phase in the correct reading frame) with a procaryotic gene.

Expression of this hybrid gene results in a fusion protein product a protein that is a hybrid of procaryotic and foreign amino acid sequences). In a specific embodiment where the Plasmodium epitope is expressed as part of a fusion protein, the Plasmodium sequence can be fused to a heterologous immunogenic sequence. In a particular embodiment, the Plasmodium sequence can be fused to all or part of the E. coli enterotoxin subunit B.

U.S. Pat. No. 4,237,224 to Cohen and Boyer describes production of recombinant plasmids using processes of cleavage with restriction enzymes and joining with DNA ligase by known methods of ligation. These recombinant plasmids are then introduced by means of transformation and replicated in unicellular cultures including procaryotic Sorganisms and eucaryotic cells grown in tissue culture.

Because of the general applicability of the techniques described therein, U.S. Pat. No. 4,237,224 is hereby incorporated by reference into the present specification.

YI~I~PULII

WO 89/02924 PCT/US88/03376 33 Another method for introducing recombinant DNA molecules into unicellular organisms is described :y Collins and Hohn in U.S. Pat. No. 4,304,863, which is also incorporated herein by reference. This method utilizes a packaging/transduction system with bacteriophage vectors (cosmids).

5.3. IDENTIFICATION OF RECOMBINANT EXPRESSION VECTORS WHICH REPLICATE AND EXPRESS A PLASMODIUM ANTIGEN OR FRAGMENT THEREOF Expression vectors containing foreign gene inserts can be identified by three general approaches: DNA-DNA hybridization, presence or absence of "marker" gene functions, and expression of inserted sequences. In the first approach, the presence of a foreign gene inserted in an expression vector can be detected by DNA-DNA hybridization using probes comprising sequences that are homologous to the foreign inserted gene. In the second approach, the recombinant vector/host system can be identified and selected based upon the presence or absence of certain "marker" gene functions beta-galactosidase activity, thymidine kinase activity, resistance to antibiotics, etc.) caused by the insertion of foreign genes in the vector.

For example, if the Plasmodium DNA sequence is inserted within the marker gene sequence of the vector, recombinants containing the Plasmodium insert can be identified by the absence of the marker gene function. In the third approach', recombinant expression vectors can be identified by assaying the foreign gene product expressed by the recombinant. Such assays can be based on the physical, immunological, or functional properties of the gene product. For example, an ELISA can be used to detect the presence of antigenic determinants which bind the appropriate anti-Plasmodium antibody see Section 6.12, infra). Once the desired recombinant molecule is identified and isolated, it can be propagated and prepared in I "uu~ WO 89/02924 PCT/US88/03376 34 quantity by methods known in the art.

5.4. EXPRESSION BY ATTENUATED ENTEROINVASIVE BACTERIA The expression vector comprising the malaria DNA sequence should then be transferred into an attenuated enteroinvasive bacterial cell where it can replicate and be expressed. This can be accomplished by any of numerous methods known in the art including but not limited to transformation of isolated plasmid DNA into the attenuated bacterial host), phage transduction, conjugation between bacterial host species, microinjection, etc. In a preferred embodiment involving the use of a plasmid expression vector, the plasmid construction can be isolated and characterized first in E. coli K12, before transfer to a Salmonella strain, by phage transduction (Schmeiger, 1972, Mol. Gen. Genetics 119:75), because of the high transformation frequencies of E. coli K12 relative to those of Salmonella such as S. typhimurium.

Any of various attenuated enteroinvasive bacteria can be used as a vehicle to express a malaria epitope so that it is effectively presented to the host immune system, in the vaccine formulations of the present invention. The vaccine bacteria retain their invasive properties, but lose in large part their virulence properties, thus allowing them to multiply in the host without causing significant disease or disorder. Examples of enteroinvasive bacteria which, in attenuated forms, may be used in the vaccine formulations of the invention include but are not limited to Salmonella spp., enteroinvasive E. coli (EIEC), and Shigella spp. In a preferred embodiment, enteroinvasive i bacteria which reside in lymphoid tissues such as the spleen Salmonella spp.) are used. Such bacteria can invade gut epithelial tissue, disseminate throughout the reticuloendothelial system, and gain access to mesenteric lymphoid tissue where they multiply and induce humoral and WO 89/02924 PCT/US88/03376 cell-mediated immunity.

Attenuated enteroinvasive bacteria may be obtained by numerous methods including but not limited to chemical mutagenesis, genetic insertion, deletion (Miller, 1972, Experiments in Molecular Genetics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York) or recombination using recombinant DNA methodology (Maniatis, 1982, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York), laboratory selection of natural mutations, etc. Methods for obtaining attenuated Salmonella strains which are non-reverting nonvirulent auxotrophic mutants suitable for use as live vaccines are described in copending U.S. patent applications Serial No. 675,381, filed November 27, 1984, and Serial No. 798,052, filed November 14, 1985, by Stocker, which are incorporated by reference herein in their entirety.

Attenuated Salmonella which can be used in the live vaccine formulations of the invention include but are not limited to those species listed in Table I, infra.

i I LT WO 89/02924 PCT/US88/03376 36 TABLE I SALMONELLA SPECIES WHICH, IN ATTENUATED FORMS, CAN BE USED IN THE VACCINE FORMULATIONS OF THE PRESENT INVENTION S. tvphi Ty21a, Ty523, Ty541) S. typhimurium SL3261, LT241) S. paratyphi A S. paratyphi B S. enteritidis serotype dublin, strain SL1438) S. cholerae-suis For a complete description of Salmonella serotypes, see Edwards and Ewing, 1986, Classification of the Enterobacteriaceae, 4th Ed., Elsevier, N.Y.

In specific embodiments, Salmonella bacteria that have been attenuated by chromosomal deletion of gene(s) for aromatic compound biosynthesis (aro) or mutation in the galE gene can be used.

S. typhi strains such as Ty523 and Ty541 are avirulent in humans by virtue of attenuation by deletion of the genes encoding aroA and/or purA (Levine, et al., 1987, J.

Clin. Invest. 79:888). Mutants of S. dublin, such as SL1438, and of S. typhimurium, such as SL3261, can be used in the development of animal model systems, since they are capable of causing animal diseases equivalent to typhoid fever.

5.4.1. ATTENUATION BY galE MUTATIONS galE mutants can provide a source of attenuated bacteria for use in the vaccine formulations of the present t W 89/02924 PCT/US88/03376 37 invention. Such galE mutants include but are not limited to the Salmonella typhi strains Ty2, Ty21 (Hone et al., 1987, J. Inf. Dis. 156:167), and CDC10-80, and the Salmonella typhimurium strains LT-2, LT241, etc. The S.

typhi galE mutant, Ty21a, and the S. typhimurium qalE mutant, LT241, are lacking the enzyme UDP-galactoseepimerase and are deficient in two other enzymes of galactose metabolism (Germanier, R. and Furer, 1975, J.

Infect. Dis. 131:553). LPS (lipopolysaccharide) is synthesized in this strain, but toxic galactose-l-phosphate accumulates and cell lysis ensues.

5.4.2. ATTENUATION BY aro MUTATIONS aro mutants provide another potential source of attenuated bacteria. Deletions of the gene aroA result in pleiotropic requirements for phenylalanine, tryptophan, tyrosine, and the folic acid precursor, p-aminobenzoic acid, and the enterochelin precursor, dihydroxybenzoic acid. The aromatic amino acids are present in animal tissues, but p-aminobenzoic acid is absent; folic acid which may be present in animal cells is not assimilated by members of the Enterobacteriaceae. In additiol., absence of enterochelin results in a requirement for iron in aroA Salmonella vaccine strains (Stocker, et al., 1982, Develop. Biol. Standard 53:47). Thus., deletions in the aroA gene result in biochemical lesions which presumably do not affect other factors which may be important for invasiveness, thus yielding attenuated bacteria which retain invasive properties.

aro mutants which can be used include but are not limited to S. typhi strains Ty523 and Ty541, for use in vaccines for humans, and S. typhimurium SL3261 and SL1479, and S. enteriditis serotype dublin SL1438, for use in animals. (See U.S. Patent No. 4,550,081 for a description of S. typhimurium strain SL1479 and S. dublin strain WO 89/02924 PCT/US88/03376 38 SL1438.) A reliable method to achieve attenuation of Salmonella has been described (Hoiseth,.S.K. and Stocker, B.A.D., 1981, Nature 291:238; Stocker, et al., 1982, Develop. Biol. Standard 53:47; and U.S. Patent No.

4,550,081) and can be used in a particular embodiment of the invention. In this method, specific deletion mutations affecting the aromatic biosynthetic pathway are introduced by transduction. The advantage of this method is that precisely defined mutations can be engineered without the use of chemical or radiation mutagenesis. In principle, a defect in aromatic biosynthesis in Salmonella causes requirements for nutrients not present in adequate free concentrations in animal tissues to support the growth of the bacteria; hence, invading bacteria are attenuated and cannot cause disease. Because mutations are deletions of a large part of one or more genes, mutational reversion is improbable.

DETERMINATION OF IMMUNOPOTENCY OF THE PLASMODIUM EPITOPE EXPRESSED BY THE RECOMBINANT ENTEROINVASIVE BACTERIA Immunopotency of the malaria epitope in its live vaccine formulation can be determined by monitoring the immune response of test animals following immunization with the attenuated enteroinvasive bacteria expressing the 2 malaria epitope. Generation of a humoral response may be taken aj an indication of a generalized immune response, other components of which, particularly cell-mediated immunity, may be important for protection against the malaria parasite. Test animals may include mice, rabbits, chimpanzees and eventually human subjects. Methods of U introduction of the immunogen may include oral, intracerebral, intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous, intranasal or any other standard routes of immunizations. The immune response of the test WO 89/02924 PCT/US88/03376 39 subjects can be analyzed by various approaches such as: the reactivity of the resultant immune serum to malaria antigens, as assayed by known techniques, enzyme linked immunosorbant assay (ELISA), immunoblots, radioimmunoprecipitations, etc.; or protection from Plasmodium infection and/or attenuation of malaria symptoms in immunized hosts.

5.6. FORMULATION OF A VACCINE The purpose of this embodiment of the invention is to formulate a vaccine in which the immunogen is an attenuated enteroinvasive bacteria that expresses a malaria epitope so as to elicit a protective immune (humoral and/or cellmediated) response against Plasmodium infections for the prevention of malaria. The bacteria of the vaccine comprise an attenuated enteroinvasive strain that is infectious for the host to be vaccinated. Such a live vaccine can be univalent or multivalent.

Multivalent vaccines can be prepared from a single or few recombinant attenuated enteroinvasive bacteria which express one or more Plasmodium-related epitopes. The vaccine may also include bacteria that express epitopes of organisms that cause other diseases, in addition to epitopes of malaria parasites. A single enteroinvasive bacteria can express more than one malarial epitope of the same or different antigens, and/or an epitope of a heterologous pathogen. The various epitopes may be expressed within the same protein within a fusion protein), on separate proteins coded by the same or different expression vectors, or in different bacteria.

Many methods may be used to introduce the live vaccine S formulations of the invention; these include but are not limited to oral, intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous, and intranasal routes, including the natural route of infection of the parent WO 89/02924 PCT/US88/03376 wild-type bacterial strain.

In a specific embodiment, attenuated Salmonella expressing an epitope of a malarial circumsporozoite protein can be formulated as a vaccine.

5.6.1. VACCINATION STRATEGIES Malaria vaccines can be directed at a specific stage in the life cycle of the parasite. In a particular embodiment, the vaccine can be directed at the sporozoite, the stage transmitted by mosquitoes, and which initiates infection in man.

An effective anti-sporozoite vaccine would have the intrinsic advantage of completely preventing infection.

After being injected by the mosquito, sporozoites rapidly invade liver cells, where they develop into the stages which infect red blood cells and cause clinical illness.

Thus, to completely block sporozoite infection of hepatocytes, high levels of antibodies against the sporozoite should be present.

In another embodiment, the vaccine formulation of the invention can be directed against an erythrocytic stage of the malaria parasite. This vaccine can be especially valuable, since antibodies against the sporozoite stage have no effect on asexual parasite stages which infect erythrocytes, and thus a single sporozoite which escapes the anti-sporozoite antibody-mediated immune response can still initiate a clinical case of malaria. Since mortality from malaria is related to the degree of parasitemia, even a blood-stage vaccine which produced less than complete immunity and reduced the numbers of infected red blood cells would be cli-ically useful.

Another specific embodiment of the invention involves the concept of transmission blocking immunity. Antibodies against the sexual (gametocyte) stage taken in with the blood meal can block fertilization of the parasite in the WO :89/02924 PCT/US88/03376 41 midgut of the mosquito, lyse gametes and zygotes, or block development of zygotes. In a particular embodiment, such a vaccine, which offers protection to populations as opposed to individuals, can be used as apart of a multivalent vaccine in malaria control programs.

Previous work with subunit vaccines demonstrated the need for effective malaria vaccine formulations. The CS gene of P. berghei has recently been cloned and sequenced (Weber et al., 1987, Experimental Parasitol. 63:295-300; see Section 7.1, infra). The repeat region of P. berqhei contains four different octapeptides in a total of twelve units, as well as two dipeptides in a sixteen unit repeat.

A peptide consisting of two repeats of the consensus octapeptide was coupled to keyhole limpet hemocyanin (KLH).

Alternatively, the cloned gene containing approximately of the actual coding sequence of the mature gene product including all of the repeat region was expressed in E.

coli. The peptide, the recombinant protein, or gammairradiated sporozoites were used to immunize mice. Antibody titers measured by ELISA against peptide, the recombinant protein, and intact sporozoites, as well as CSP and ISI activity, were at least as high in the subunit vaccinated groups of mice as in the groups immunized with irradiated sporozoites. Significantly, only the irradiated sporozoite-immunized animals could be protected against high sporozoite challenge (104). Subunit vaccinated animals were protected only at the lowest sporozoite challenge dose (500). Protection was only partial and never exceeded 40% (Egan, et al., 1987, Science 236:453).

In recent studies, we have shown that transfer of T cells from sporozoite-immunized mice protected recipient animals, but mice receiving B cells or '-lyclonal immune sera were not protected, thus suggest .hat cellular immunity is important.

M-k WO 89/02924 PCT/US88/03376 42 The vaccine formulations of the present invention provide protective immunity against malaria, as a result of the expression of malaria epitopes in attenuated enteroinvasive bacteria, which allows the induction of cell-mediated immunity (CMI), in addition to humoral immunity.

We speculate that in the normal course of immunization with sporozoites, antibody prevents some but not all the sporozoites from reaching the liver. Sporozoites deposit CS protein on the surface of hepatocytes when they invade and developing exoerythrocytic forms (EE) express epitopes recognized by mAbs raised against sporozoites. These developing EE forms would be likely targets for natural killer cells and cytotoxic T cells or cytokine mediated responses. The failure of parenterally administered subunit CS vaccines to induce protective cellular responses may be a result of inappropriate antigen presentation in association with the MHC (major histocompatibility) molecule, or alternatively could indicate that epitopes critical to sporozoite induced immunity are not present on the CS protein. However, the latter explanation is unlikely, since the CS protein is the only known detectable surface antigen. The likelihood that targeting of the organism to a particular cell type and subsequent presentation of antigen in conjunction with the appropriate MHC molecule may be critical for induction of CMI is supported by the fact that protective immunization against sporozoite challenge requires the intravenous administration of intact, attenuated sporozoites. Neither intramuscular immunization nor use of the freeze-thawed or sonicated organisms induces significant protection (Spitalny, G.L.

and Nussenzweig, 1972, Proc. Helm. Soc. Wash.

39:506).

A solution to this problem is to deliver the expressed CS protein (or other malarial antigen, or epitopes thereof) WO 89/02924 PCT/US88/03376 43 in an attenuated organism which can facilitate delivery to appropriate antigen-presenting cells, as provided by the vaccine formulations of the present invention. A preferred embodiment of the invention is-the use of an avirulent non-pathogenic Salmonella oral vector delivery system. Use of this system can not only preclude some of the potential side effects associated with the use of other delivery vehicles such as vaccinia virus, but can also provide for convenient oral administration of malaria vaccines. This latter point is crucial for developing countries with limited health resources that are unable to support multiple administration of parenterally administered vaccines.

5.6.2. ORAL VACCINATION WITH ATTENUATED SALMONELLA In a particular embodiment of the present invention, the concept of using attenuated species of Salmonella to deliver foreign antigens is based on the ability of Salmonella spp. to invade gut epithelial tissue and thereby gain access to mesenteric lymphoid tissue. In the mouse typhoid model, Takeuchi (1975, in Microbiology, American Society for Microbiology, Washington, pp. 174-181) has shown that following the attachment of S. typhimurium at the luminal brush border, bacteria invade the villus tip and become engulfed in pinocytized membrane vacuoles.

Crossing the distal membrane of epithelial cells, the bacteria can disseminate throughout the reticuloendothelial system. When they reach the lamina propria, Salmonella cells cause an influx of macrophages which ingest the bacteria. Some cells escape phagocytosis and drain into mesenteric lymph nodes where they multiply. We postulate that stimulation of cell mediated responses is a consequence of invasion of the reticuloendothelial system.

Thus, an innate feature of the attenuated oral vaccines of the invention is that they be able to invade the intestinal WO 89/02924 PCT/US88/03376 44 epithelium as can a pathogenic organism, but fail to cause active disease because of a precisely defined genetic lesion), resulting in loss of pathogenicity. Oral malaria vaccines based on Salmonella have several advantages over vaccines now being developed. For example, with the appropriate genetic construction, the vector can mimic the sporozoite in surface presentation of the antigen and stimulate both cell-mediated and humoral immunity. Purification steps of a recombinant protein is not necessary, and the live attenuated Salmonella vaccine can be cheaply produced and conveniently administered in a lyophilired form). In addition, the probability of adverse reactions based on available animal and human studies is low (Germanier, 1984, in Bacterial Vaccines, Academic Press, New York, pp. 137-165; Gilman, et al., 1977, J. Infect. Dis. 136:717; Levine, et al., 1983, Microbiol. Rev. 47:510; Smith, et al., 1984, Am. J. Vet.

Res. 45:2231; Smith, et al., 1984, Am. J. Vet. Res.

45:59; Wray, et al., 1982, Develop. Biol. Standard 53:41; Wray, et al., 1977, J. Hyg. Camb. 79:17).

6. EXAMPLE: MATERIALS AND METHODS 6.1. CONDITIONS FOR RESTRICTION ENZYME DIGESTIONS Restriction endonucleases were purchased from BRL (Bethesda Research Laboratories, Bethesda, MD), IBI (International Biotechnologies, Inc., New Haven, CT), New England Biolabs (Beverly, MA), or U.S. Biochemical Corporation (Cleveland, OH).

Restriction enzyme digestions were carried out by suspending DNA in the appropriate restriction buffer, adding restriction endonuclease, and incubating for an appropriate period of time to ensure complete digestion.

One unit of enzyme is defined as the amount required to completely digest 1.0 ug of phage lambda DNA in 1 hour in a WO 89/02924 PCT/US88/03376 total reaction mixture of 10 ul volume. Buffers used with the various enzymes are listed below: Low salt buffer used for Clal, HpaI, HpaII, and KpnI digestions consisted of: 10 mM Tris-Cl (pH 10 mM MgCl 2 and 10 mM dithiothreitol (DTT).

Medium salt buffer used for AluI, Aval, SspI, TaqI, XmaI, and XmnI digestions consisted of: 50 mM Tris-Cl (pH 10 mM MgCl 2 50 mM NaC1, and 10 mM DTT.

High salt buffer used for BamHI, EcoRI, EcoRV, NcoI, and SalI digestions consisted of: 50 mM Tris-C1 (pH 10 mM MgC1 2 150 mM NaCI, and 10 mM DTT.

The buffer used for SmaI digestions consisted of: mM Tri-Cl (pH 20 mM KC1, 10 mM MgCl 2 and 10 mM DTT.

All restriction digestions were carried out at 37'C except TaqI, which was carried out at 6.2. GEL PURIFICATION OF DNA FRAGMENTS After restriction enzyme digestions, DNA fragments of varying sizes were separated and purified by gel electrophoresis in agarose using 0.1 M Tris-Borate buffer (pH containing 2 mM EDTA at 10 volts/cm. Agarose concentrations varied from 0.8% to 1.5% depending on the size of the fragments to be recovered. DNA bands were visualized by ethidium bromide fluorescence. DNA was recovered by electroelution of the chosen DNA fragment onto NA45 paper (Schleicher and Schuell, Keene, New Hampshire), followed by incubation of the NA45 paper at 68*C in a buffer consisting of 10 mM Tris (pH 1 mM EDTA and 1 M NaCl.

6.3. SYNTHESIS AND PURIFICATION OF OLIGONUCLEOTIDES Oligonucleotides were synthesized on the 0.2 micromole scale, on an Applied Biosystems Inc. model 380B DNA synthesizer, using beta-cyanoethyl-phosphoramidite chemistry (Sinha, et al., 1984, Nucl. Acids Res.

12:4539-4544).

WO 89/02924 PCT/US88/03376 fd 46 Oligonucleotides were purified by electrophoresis in a 0.4 mm thick 8% polyacrylamide gel in TBE buffer (0.01 M Tris-borate, pH 8.2, 1 mM EDTA), run at approximately 1600 volts with a constant power of 75 watts. Oligonucleotide bands were visualized by negative shadowing over a PEI (polyethylene-imine) thin-layer chromatography plate under ultraviolet light, and the band of full length product was excised from the gel. The synthetic oligonucleotide was eluted in 0.3 M sodium acetate pH 5.5, and was precipitated by the addition of two volumes of 100% ethanol, chilled to -20*C, and centrifuged at 14,000 X g. The DNA pellets were dried under vacuum and dissolved in TE buffer (10 mM Tris- Cl, pH 7.4, 1 mM EDTA).

Phosphate groups were incorporated at the 5' terminus of the synthetic oligonucleotides using T4 polynucleotide kinase (New England Biolabs, Beverly, MA). One Licrogram amounts of purified oligonucleotide were dissolved in microliters of kinase buffer consisting of 70 mM Tris-Cl (pH 10 mM MgC1 2 5 mM DTT, with 1 mM adenosine triphosphate (ATP). This solution was incubated with units T4 polynucleotide kinase for 30 minutes at 37°C.

Annealing of complementary strands was achieved by mixing the kinased strands and heating to 60 0 C for 1 hour and cooling to room temperature. Annealed strands were used directly in ligation procedures.

6.4. CREATION OF FLUSH ENDS IN DNA FRAGMENTS To create blunt ends for ligation, DNA termini with overhangs resulting from digestion with restriction enzymes, were either filled-out by the action of the large fragment of DNA polymerase I (Klenow fragment), or removed by the action of mung bean nuclease. For filling-out with Klenow enzyme, approximately 1 microgram of DNA was treated with 1 unit of enzyme in 25 microliters of a buffer consisting of 50 mM Tris-Cl (pH 10 mM MgSO 4 0.1 mM WO 89/02924 PCT/US88/03376 47 dithiothreitol, and 50 ug bovine serum albumin per ml. A combination of deoxynucleotide triphosphates (dGTP, dCTP, dATP, dTTP) at a final concentration of 100 micromolar was also included. For digestion with mung bean nuclease, approximately 1 microgram of DNA was incubated with 1 unit of mung bean nuclease in 20 microliters in a buffer consisting of 50 mM sodium acetate (pH 30 mM NaCl, and 1 mM ZnSO 4 Incubation was at 30'C for 0.5 to 1 hour.

mung bean nuclease and Klenow enzyme were obtained from New England Biolabs, Beverly, MA).

DNA LIGATION All ligations were accomplished using T4 DNA ligase.

T4 DNA ligase was purchased from BRL (Bethesda, MD), U.S.

Biochemical Corporation (Cleveland, OH), or Boehringer (Indianapolis, IN). One unit of T4 DNA ligase is defined as the amount required to yield 50% ligation of HindIII fragments of bacteriophage lambda DNA in 30 minutes at 60'C in 20 ul volume ligase buffer at a 5°-DNA termini concentration of 0.12 uM (300 ug/ml). DNA ligations were performed in ligase buffer consisting of 50 mM Tris-Cl (pH 10 mM MgCl 2 10 mM DTT, and 1 mM ATP. Normally, DNA concentration ranged from 20-30 ug/ml. T4 DNA ligase was added at a ratio of 1 U per 20 ul reaction volume. Incubations were carried out for 18-24 hours. Temperatures used were 15*C for cohesive end ligations, and 22°C for blunt end ligations. If sufficient material was available, ligations were checked by analyzing a portion of the reaction mixture by agarose gel electrophoresis.

6.6. TRANSFORMATION OF PLASMID DNA Plasmid constructions resulting from the ligation of fragments of circumsporozoite genes (or synthetic oligonucleotides related to such gene sequences) to cloning or expression vectors, were inserted into common laboratory WO 89/02924 PCT/US88/03376 48 strains of Escherichia coli by transformation techniques (for details, see Maniatis et al., 1982, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York). Plasmid constructions were isolated and characterized first in E. coli, before transferring to Salmonella spp., because of the high transformation frequencies of E. coli K-12 relative to those of S. typhimurium. Plasmids were transferred into S. typhimurium LT-2 LB5010, a strain lacking several of the restriction systems known to exist in various Salmonella species and also containing a mutation in galE resulting in higher transformation frequencies (for a description of restriction systems of Salmonella typhimurium, see Bullas et al., 1980, J. Bacteriol. 141:275). Plasmids transformed into LB5010 were characterized for expression of the desired CS protein construct and, after verification by restriction enzyme analysis, plasmids were inserted into attenuated Salmonella by transduction techniques. LB5010 containing desired plasmid was grown in Luria broth (LB) to a density of 3 x 10 cells/ml, at which point D-galactose (to a final concentration of was added to the growth medium to induce synthesis of lipopolysaccharide (LPS).

Following 1.5 hours of growth in the presence of D-galactose, bacteriophage P22 HT 105/1 int was added to the culture to a multiplicity of infection of one. Fol,;owing adsorption of the phage, cells were immobilized in LB containing 0.7% agar. Phage were harvested and used to transduce plasmids into any attenuated Salmonella containing LPS as a component of the receptor for the transducing phage P22.

6.7. SYNTHESIS AND PURIFICATION OF CS IMMUNODOMINANT PEPTIDES To demonstrate antigenicity or immunogenicity of subunit vaccines when compared to live attenuated Salmonella carrying CS proteins, two synthetic peptides, WO 89/02924 PCT/US88/03376 49 one representing two repeat units of circumsporozoite (CS) protein from Plasmodium berahi (DPAPPNAN; D-16-N) and the second representing 3 repeat units of CS from Plasmodium falciparum [(NANP)3] were synthesized by the solid phase method on an automatic peptide synthesizer (Applied Biosystem Model 430A). Synthetic peptides also served as capture antigens in ELISA assays.

The peptide chain was assembled on an insoluble polystyrene resin to which the carboxy terminal amino acid was attached through a special organic spacer known as "PAM" linker. Amino acids, protected with t-butyloxycarbonyl (BOC), were coupled to the free alpha-amino groups on the growing peptide chain in an aprotic, polar solvent.

Premature chain termination and peptide self-aggregation on the resin support was minimized by keeping the peptide chain dissolved in dimethylformamide during the coupling steps. The coupling reaction was monitored by a quantitative ninhydrin procedure which measures residual free alpha-amino groups on the peptide resin. All reactive side chains of individual t-BOC amino acids were protected with benzyl based protecting groups.

The completed peptides were cleaved from the resin, and all side-chain protecting groups were removed by anhydrous hydrofluoric acid (HF) treatment. After strong acid cleavage and deprotection, the reaction mixture was washed well with anhydrous ether and dissolved in dilute acetic acid. The resin was filtered, and the aqueous solution was collected and lyophilized to yield the crude peptide preparation.

The homogeneity of the peptide obtained from HF cleavage was evaluated on a micropore HPLC (high performance liquid chromatography) system (Applied Biosystems Model 130A separation system) using a reverse phase column.

If HPLC analysis revealed a single major peak, no further purification was performed. If the HPLC chromatogram i 1 i WO 89/02924 PCT/US88/03376 showed a mixture of peaks, preparative HPLC was performed to separate peaks. The purified product was subjected to acid hydrolysis for amino acid analysis to verify the amino acid composition. The synthetic peptides were sequenced by automated Edman degradation with a protein sequenator (Applied Biosystems Model 477A) equipped with a fully automatic on-line phenylthiohydantoin (PTH) analyzer (Model 120A).

6.8. PEPTIDE-KEYHOLE LIMPET HEMOCYANIN CONJUGATION PROCEDURE Synthetic peptides were coupled to keyhole limpet hemocyanin (KLH) by glutaraldehyde cross-linking. KLH (obtained from Calbiochem, San Diego, CA) was dialysed against 0.1 M sodium bicarbonate buffer (pH 9.6) and adjusted to 1 mg/ml in the same buffer. Peptides were made in water or 0.1 M sodium bicarbonate buffer at 4 mg/ml.

Equal volumes of protein and peptide solutions were mixed and rotated for 1 hour at room temperature. Four microliters of 25% aqueous solution of glutaraldehyde was added and rotated for another 24 hours, followed by another microliters of 25% glutaraldehyde and rotation for 72 hours at room temperature. The conjugated material was dialysed against phosphate-buffered saline for 24 hours. Peptide- KLH conjugates were tested in ELISA, as -previously described (Egan et al., 1984, Science 236:453). Initially, plates were coated with different concentrations of conjugates, and the concentration that reacted well with the appropriate monoclonal antibodies was selected for coating plates in all future experiments.

6.9. POLYACRYLAMIDE GEL ELECTROPHOPESIS To analyze proteins by polyacrylamide gel electrophoresis (PAGE), cells from 1-ml of culture were washed and resuspended in 100 microliters of a lysing buffer (0.2 M Tris-HCl buffer containing 5% SDS, 0.025% bromophenol blue,

'A

WO 89/02924 PCT/US88/03376 51 0.1 to 1 M 2-mercaptoethanol, and 20% glycerol), and heated for 5 minutes at 100'C. Most analyses were performed using the Bio-Rad Mini Protean Gel system (Redmond, CA). Gels were 1.5 mm thick, and the separating gel contained acrylamide, with an acrylamide to bis-acrylamide ratio of 30:0.8, 0.375 M Tris-HCl (pH and 0.1% sodium dodecyl sulfate (SDS). The stacking gel contained 4.8% acrylamide with the same 30:0.8 ratio of acrylamide to bis-acrylamide, 125 mM Tris-HCl (pH and 0.1% SDS.

Ten to fifteen microliters of samples (containing 5-20 micrograms protein) were applied to each lane. Following electrophoresis, gels were stained for at least 1 hour with 0.125% Coomassie blue in ethanol:acetic acid:water then destained in the same solvent system without the dye.

Pre-stained low molecular weight standards (ovalbumin, 43,000; alpha-chymotrypsinogen, 25,700; B-lactoglobulin, 18,400; lysozyme, 14,300; bovine trypsin inhibitor, 6,200; insulin, 2,300 and 3,400; obtained from Bethesda Research Laboratories, Gaithersburg, MD) were also subjected to electrophoresis to assist in the determination of the relative molecular weight of the observed proteins. An unstained duplicate gel without staining was used for western analysis.

6.10. WESTERN BLOT AND ISOELECTRIC FOCUSSING ANALYSIS Samples separated by PAGE were transferred electrophoretically onto nitrocellulose membranes in a Hoeffer Tra sphor apparatus at 0.45 milliamps for 90 minutes in mM Tris, 384 mM glycine (pH 8.8) at room temperature. Once protein transfer was complete, nitrocellulose membranes were soaked in BLOTTO non-fat dry milk in phosphatebuffered saline) at 37C for 1 hour. Membranes were probed with a pre-determined concentration of monoclonal antibodies against P. berghei or P. falciparum CS protein repeat regions for 1 hour at 37'C and washed with BLOTTO WO 89/02924 PCT/US88/03376 52 for 20 minutes at 37*C, Bound antibodies were detected by incubation with horseradish peroxidase-conjugated goat anti-mouse IgG (Kirkegaard and Perry, MD) at 1:250 dilution in BLOTTO for 1 hour at 37'C. Blots were washed three times with PBS, and developed with PBS containing 0.01% S hydrogen peroxide, 0.06% 4-chloro-1 napthol (Sigma Chemical Co., MO), in methanol for 20 minutes at room temperature.

The reaction was stopped by transferring the filters to distilled water. The filters were dried by blotting.

For isoelectric focussing of proteins in polyacrylamide gels, approximately 10-50 micrograms of total cell proteins were applied to the gel. Cell extracts were prepared by harvesting bacteria in the logarithmic phase of growth, and concentrating them fifty-fold by centrifugation and resuspension in 0.5 ml of 10 mM Tris- HCl., pH 8.0, containing 1 mM EDTA and 20 ug lysczyme per ml. After digestion with lysozyme, extracts were subjected to sonication. Whole cells and cellular debris were removed by centrifugation at 12,000 x g, and the supernatant samples, in a volume of 10-50 microliters, were applied to an isoelectric focussing gel in a sample buffer consisting of 10% v/v glycerol, 2% carrier ampholytes (pH 3-10) and 0.001% methyl red. Focussing gels consisted of acrylamide containing 2% ampholytes C (pH 3-10; purchased from BioRad, Richmond, CA). Focussing of proteins was carried out over a 4-5 hour period at 2000 V.

Focussed proteins were transferred to nitrocellulose by electroblotting, followed by visualisation with monoclonal antibody to the CS protein repeat region as described supra for the western blot technique.

6.11. COLONY BLOT SCREENS FOR CIRCUMSPOROZOITE PROTEIN EXPRESSION IN E. COLI E. coli transformant colonies were screened for expression of the immunodominant CS epitope by lysing cells retained on nitrocellulose filters by exposure to chloro- .I WO 89/02924 PCT/US88/03376 53 form vapors for a period of 20 minutes. Lysed colonies were washed off the nitrocellulose filter by immersing the filters in a blocking solution consisting of 50 mM Tris-Cl, pH 8 0, containing 0.15 M NaCl, 5 grams of Carnation instant dried milk (BLOTTO) per 100 ml of solution, 1 microgram boiled RNase per ml, 1 microgram DNase per ml, and 200 micrograms egg white lysozyme per ml. Filters were washied further in BLOTTO, and monoclonal antibody 3.28 (Egan et al., 1987, Science 236:453), capable of recognizing the immunodominant repeated epitope of P. berghei, or a mixture of two or more monoclonal antibodies, mAb 4D9.1P or mAb 565, reacting with the repeat epitope of P.

falciparum (Dame et al., 1984, Science 225:593), was added to a concentration of 10-100 nanograms per ml of blocking solution. Filters were incubated for 1 hour at 37'C, followed by washing in BLOTTO. The bound antibody was amplified by addition of rabbit anti-mouse IgG antibody, and incubation for another hour at 37'C. The signal was developed by incubation with goat anti-rabbit IgG coupled to horseradish peroxidase. Horseradish peroxidase was visualized by reaction in the presence of 0.06% 4-chloro- 1-napthol and 0.15% hydrogen peroxide 6.12. ENZYME-LINKED IMMUNOABSORBENT ASSAY FOR SERUM ANTI-CS AND ANTI-LT-B ANTIBODIES To measure serum antibodies, 96 well polystyrene plates (NUNC) were coated with 1 ug/ml of LT-B or 5 ug/ml of D-16-N-KLH, a synthetic peptide representing two repeat units of Plasmodium berghei CS protein coupled to KLH by glutaraldehyde cross-linking. Each well received 0.1 ml of antigen in 0.1 M carbonate/bicarbonate buffer (pH 9.6).

Plates were incubated at 37*C in a humidified incubator for 18 hours, before being washed 3 times with PBS containing 0.05% Tween 20 (PBS-T) and blocked with 0.1% gelatin in PBS for 60 minutes at room temperature. Plates were washed 3 times with PBS-T, and serial dilutions of sera were added -i rrTU/ 0 fi3376 W i-

*V

VO 89/02924 1 54 and incubated for 90 minutes at room temperature. Goat anti-LT-B or mAb 3.28, or pools of mAb 4D9.1P and mAb 565, were used as positive controls in assays. Plates were washed as before, and pre-optimized concentrations of alkaline phosphatase-conjugated rabbit anti-goat immunoglobulin (at a 1:3000 serum dilution; Tago, Burlingame, CA), and goat anti-mouse immunoglobulin (at a 1:5000 serum dilution; Tago, Burlingame, CA) were added to appropriate wells and incubated for 60 minutes at room temperature.

Plates were washed again, and 100 microliters of substrate solution (p-nitrophenyl phosphate at 1 mg/ml in diethanolamine buffer, pH 9.6) was added to each well. The signals were developed for 60 minutes at room temperature, and read in a Bio-Tek automatic ELISA reader using dual wavelengths at 410 nm and 690 nm, blanking on air.

6.13. CHALLENGE OF MICE WITH LIVE SPOROZOITES Sporozoites of Plasmodium berqhei were obtained from salivary glands of infected female Anopheles mosquitoes.

The salivary glands were dissected out and collected in ice-cold tissue culture medium M199 supplemented with normal mouse serum. The glands were gently triturated in a loose-fitting glass grinder. Sporozoites were separated from mosquito tissue debris by centrifuging triturated glands at 500 rpm in a Sorvall SS34 rotor for 3 minutes at 4'C and collecting parasite-containing supernatant. For maximum yield, the extraction was repeated twice. The concentration of sporozoites was determined by counting the parasites in a hemocytometer.

Seven to 14 days after the final vaccination, animals were divided into Sub-groups and challenged with a low dose (500) or high dose (2000) of sporozoites of Plasmodium berghei. Starting from day 3 after challenge, mice were examined daily for mortality and for detectable parasitemia in Giemsa-stained blood smears. All patent infections WO 89/02924 PCT/US88/03376 usually appeared within 10 days after challenge.

7. EXAMPLE: EXPRESSION VECTORS FOR PLASMODIUM CIRCUMSPOROZOITE PROTEIN GENES 7.1. DNA SEQUENCE OF THE GENE FOR THE P. BERGHEI CIRCUMSPOROZOITE PROTEIN The gene encoding approximately 75% of the carboxyterminal portion of the circumsporozoite protein of P. berghei was obtained as an 1140 base pair EcoRI restriction fragment in the plasmid vector pUC8 (Veira, J. and Messing, 1982, Gene 19:259). The DNA sequence of the fragment has been previously determined (Weber et al., 1987, Experimental Parasitol. 63:295), and is depicted in Figure 1, with the deduced amino acid sequence listed in Figure 2. In addition to the sequence shown in Figure 1, an EcoRI-TaqI oligonucleotide linker was used during the initial cloning and is contained within the EcoRI restriction fragment. This adapter, or linker region, contains nucleotide sequences which comprise recognition sites for restriction endonuclease cleavage. These restriction enzyme sites can be used as convenient cleavage sites for subcloning the gene sequence into expression vectors. The sequence of the adapter region is as shown (the adapter sequences are underlined): 2b circumsporozoite protein gene TaqI Nrul XmnI AATTCGAACCCCTTCG CGCGAAGGGGTTCGAATT 3' m Nru XmnI Nrul TaI WO 89/02924 PCT/US88/03376 56 7.2. CONSTRUCTION OF PLASMID pPX100, EXPRESSING LT-B UNDER THE CONTROL OF THE lac OPERON Plasmid pJC217 encodes 100 amino acids of mature E. coli enterotoxin subunit B, LT-B, and also encodes a amino acid amino-terminal signal sequence which is cleaved from the mature molecule. Plasmid pJC217 was obtained by insertion of approximately 800 base pairs of LT-B DNA (the sequence of which is shown in Fig. from a genomic fragment of enterotoxigenic E. coli H10407, into the HindIII site of plasmid vector pUC8.

To obtain an expression vector in which fusions of the circumsporozoite protein of P. berghei with various regions of LT-B can be created, plasmid pJC217 was modified to delete extraneous restriction sites associated with the polylinker region of pUC8. By digesting pJC217 with the restriction enzyme EcoRI and religating the reaction products, a deletion of 180 base pairs of DNA including the DNA specifying the restriction sites of the polylinker region was obtained, resulting in plasmid vector pPX100 (Fig. In this configuration, LT-B is controlled by the lac operon promoter of E. coli. After transfer of the plasmid into a suitable bacterial host, E. coli JM103 (Clements et al., 1984, Infect. Immun. 46:564), LT-B transcription can be induced by inclusion of isopropylthio-beta-D-galactoside (IPTG) in the growth medium of the recombinant bacteria. The DNA sequence of LT-B is depicted in Figure 3; restriction enzyme sites useful in creating fusion protein molecules are indicated.

7.3. EXPRESSION OF THE CIRCUMSPOROZOITE PROTEIN OF P. BERGHEI IN E. COLI, AS A FUSION PROTEIN WITH BETA-GALACTOSIDASE To obtain expression of the circumsporozoite protein gene in E. coli, plasmid pUC8 containing the 1.1 kilobase pair EcoRI CS fragment was digested with either Nrul or XmnI under standard conditions for those enzymes. A 670 l WO 89/02924 PCT/US88/03376 57 base pair XmnI fragment was purified by electrophoresis through a 1% agarose gel and eluted from agarose by electrophoresis onto NA45 paper (Schleicher and Schuell, Keene, New Hampshire). The DNA fragment was eluted off of the NA45 paper by incubating the paper in a 250 microliter volume of 10 mM Tris hydrochloride buffer, pH 8.0, containing 1 M NaCl and 5 mM EDTA. DNA was precipitated from the NaCl buffer by addition of two volumes of ethanol, and the DNA pellet was obtained by centrifugation at 12,000 x g for minutes at 4'C. The 1.1 kilobase pair Nrul fragment was purified in the same fashion. The XmnI and NruI DNA fragments were each redissolved in a sufficient volume of mM Tris hydrochloride containing 10 mM EDTA to yield a final concentration of approximately 1 microgram per microliter. Plasmid vector pUC8 was digested with HincII and mixed either the with purified XmnI or the NruI fragment, and the DNA ends were joined with T4 DNA ligase. The ligation products were transformed into E. coli JM103, with selection for resistance to ampicillin.

7.3.1. DETECTION OF TRANSFORMANT COLONIES EXPRESSING THE REPEATED EPITOPE OF THE CIRCUMSPOROZOITE PROTEIN Transformant bacterial colonies reacting with mAb 3.28, an antibody which recognizes the immunodominant repeated epitope of P. berghei CS, were detected by the colony blot method described in Section 6.11, following induction of lac operon expression by transfer of the colonies to an LB agar plate containing 1 mM IPTG.

After transformation with the plasmid resulting from religation of pUC8 restricted by the enzyme HincIl in the presence of either the 1.1 kilobase pair NruI CS fragment or the 670 base pair XmnI CS fragment, as described above, approximately 10% of the resulting transformants demonstrated significant color development when reacted with mAb 3.28. Among the reactive colonies from each ligation, WO 89/02924 PCT/US88/033 7 6 58 several candidates were retained and analyzed further.

Plasmids isolated from each candidate colony were subjected to restriction enzyme analysis to confirm the presence of characteristic cleavage sites. Plasmid pPX1512 results from the linkage of the 670 base pair XmnI fragment in frame with the first eleven amino acids encoded by the polylinker region of pUC8, and reads in-frame through the 223 amino acids encoded by the DNA of the XmnI fragment through the following sixty-eight amino acids of the betagalactosidase peptide, termed the lac alpha peptide, encoded in the pUC8 vector. Plasmid pPX1514 results from the linkage of the 1.1 kilobase pair NruI fragment into the HincII site of pUC8, and contains a fusion of the first eleven amino acids of the polylinker region to 272 amino acids of the circumsporozoite protein. The translated protein of pPX1514 terminates with the translation termination codon TAA supplied in the circumsporozoite protein sequence.

7.4. FUSION OF THE P. BERGHEI CIRCUMSPOROZOITE PROTEIN TO THE CARRIER POLYPEPTIDE LT-B The circumsporozoite gene of P. berghei was linked to the gene for the B subunit of E. coli enterotoxin, LT-B, at three separate loci within the gene sequence. As diagrammed in Figures 5 and 6, pPX100 was cut with three separate restriction enzymes by standard techniques, and the resulting cohesive ends were modified so that blunt-end ligation of either the XmnI or the NruI fragment containing the repeat regions of the circumsporozcite gene would result in in-frame fusion of the CS gene with regions of the LT-B gene contained in pPX00. First, pPX100 was cut with ClaI and the cohesive ends "filled- out" by the action ii of the Klenow fragment of DNA polymerase I in the presence of dCTP and dGTP. When the 670 base pair XmnI CS fragment was ligated to the modified Clal site, an LT-B fusion protein resulted. This protein, as encoded in pPX1515, WO 89/02924 PCT/US88/03376 59 comprises the first 30 amino acids of mature LT-B fused to 223 amino acids of the CS gene, followed by an out-of-frame readthrough of twenty-eight amino acids derived from LT-B DNA downstream from the Clal site. When the 1.1 kilobase pair NruI fragment was ligated to the modified Clal site, a protein resulted in which the first thirty amino acids of mature LT-B were fused with 272 amino acids of the CS gene, with translation terminating with the termination codon of the CS gene.

Equivalently, pPX100 was digested with XmaI and treated further with mung bean nuclease to remove the overhanging 5' terminus. The 1.1 kilobase pair NruI CS fragment was ligated to this modified site, yielding plasmid pPX1523. The resulting fusion protein contained sixty amino acids of mature LT-B linked to 223 amino acids of the CS gene, followed by an out-of-frame readthrough of four amino acids derived from LT-B DNA. To fuse the CS protein sequences to the carboxy-terminal amino acid of mature LT-B, pPX100 was digested with the restriction enzyme SpeI. The resulting cohesive termini were partially filled in by the action of the Klenow enzyme of DNA polymerase I in the presence of dCTP, and the remaining overhang was digested with mung bean nuclease. Blunt-end ligation of either the 1.1 kilobase pair Nrul or the 670 base pair XrnI CS fragment resulted in the fusion proteins depicted in Figure 6. Plasmid pPX1525 encodes a LT-B/CS fusion protein in which 100 amino acids of mature LT-B is linked to 223 amino acids of the CS protein, followed by forty amino acids read out-of-frame, which are derived from DNA present in the LT-B clone,(outside the coding region of

LT-B).

WO 89/02924 PCT/US88/03376 MANIPULATION OF TRANSCRIPTIONAL PROMOTER AND TRANSLATION INITIATION SIGNALS TO OBTAIN HIGHER LEVELS OF LT-B/CS FUSION PROTEIN EXPRESSION Increased expression of LT-B CS fusion proteins was obtained by inserting the fused gene sequences directly downstream from either of two strong promoter sequences known to function well in E. coli. The tac promoter results from the fusion of the -35 region of the trp operon promoter with the -10 region of the UV5 lac promoter (DeBoer, et al., 1982, in Promoter Structure and Function, Rodriguez, R.L. and Chamberlain, eds., Praeger Publishing, New York). The tac promoter is controlled by the lacI gene product, a repressor which binds to the lac region of the DNA and inhibits transcription by RNA polymerase. In the presence of the lacI gene product, gene expression can be induced by IPTG present in the bacterial growth medium. The PL promoter of coliphage lambda controls leftward transcription of mRNA during lytic growth of the virus in its natural host, E.

coli (Shimatake, H. and Rosenberg, 1981, Nature 292:128). The PL promoter is repressed during lysogeny by the cI gene repressor protein. When either the tac promoter or the PL promoter is used to drive gene transcription in a closely related enteric host bacterium such as Salmonella spp., gene transcription is constitutive unless appropriate repressor functions are also introduced.

Gene transcription results in constitutive synthesis of proteins encoded by DNA downstream from the promoter sequences. Synthesis of antigenic proteins in a Salmonella spp. host, such as the LT-B/CS fusion proteins described in Section 7.4, results in constant presentation of the antigenic molecules during the period of time the attenuated bacteria can replicate within the animal host, either in the experimental test animal such as the mouse, i IWO 89/02924 PCT/US88/03376 61 or in humans. A high level of specific protein synthesis relative to endogenous bacterial host proteins favors host immune response to the recombinant DNA-derived proteins.

To demonstrate increased synthesis of equivalent proteins expressed in Salmonella spp., each of the family of LT-B/CS fusion proteins diagrammed in Figure'6 was inserted directly downstream from either the tac promoter (Fig. 7) or the PL promoter (Fig. The translation initiation signals derived from LT-B are retained within the EcoRI-HindIII fragments encoding the LT-B/CS fusion proteins and include a ribosome binding site (S/D sequence) and the translation start codon of LT-B at the 5' terminus of the gene sequence (Fig. Plasmid vector pKK223 (purchased from Pharmacia Molecular Biologicals, Piscataway, NJ) contains the tac promoter, but lacks suitable translation start sequences downstream from the promoter. Plasmid pKK223 was digested with restriction enzymes EcoRI and HindIII. The plasmid vector fragment was purified by electrophoresis through agarose and was ligated to purified EcoRI-HindIII restriction fragments derived from either pPX1515, pPX1523, or pPX1525. Transformants obtained in E. coli JM103 were screened for production of proteins reactive to the specific anti-CS monoclonal antibody, mAb 3.28, after transfer of bacterial colonies to LB agar containing 1 mM IPTG. Reactive colonies were purified, and DNA isolated from them was screened further by restriction enzyme analysis. Those colonies showing the expected DNA restriction patterns were retained. As diagrammed in Figure 7, plasmid pPX1528 was obtained in this fashion.

To obtain expression of an equivalent family of fusion proteins controlled by the PL promoter of coliphage lambda, the EcoRI-HindIII restriction fragments derived from pPX1515, pPX1523, and pPX1525 were treated with the Klenow fragment of DNA polymerase I in the presence of dATP, dTTP, j WO 89/02924 PCT/US8/03376 62 dCTP, and dGTP, to create blunt ends at both the EcoRI end and the HindIII end of the fragments (Fig. By ligatirg the blunt-ended fragments into the HpaI site of plasmid vector pPL-lambda (Pharmacia), a series of plasmids encoding fusion proteins controlled by the PL promoter was obtained by transforming E. coli N99 cI+. Plasmid pPX1601 was derived from a fragment of pPX1515, ligated into expression vector pPL-lambda (Fig. Transformants were screened in E. coli for the presence of unique restriction fragments. Suitable candidates were then transformed into E. coli strain N4830, which is lysogenic for a defective bacteriophage lambda harboring a temperature-sensitive repressor allele, ci857. In this E. coli host strain, genes controlled by the lambda PL promoter are inducible by switching the temperature of the growth medium from 32*C to 42*C. As depicted in Figure 8, in this configuration, translation initiation signals are supplied by the S/D sequence and translation initiation codon (ATG) derived from LT-B. The vector also encodes part of the bacteriophage lambda N gene, whose transcription is controlled by the PL promoter. By inserting the blunt ended EcoRI-HindIII fragment of the LT-B/CS fusion proteins in the Hpal site, the N gene terminates with the TGA codon immediately after the S/D sequence as shown in Figure 8.

7.6. CONSTRUCTION OF EXPRESSION VECTORS TO PROMOTE TRANSCRIPTION FROM THE LAMBDA P PROMOTER OF GENES ENCODING CIRCUMSPOROZOiTE PROTEINS To provide suitable translation initiation signals downstream from the PL promoter, an oligonucleotide was designed to be inserted into the HpaI site of pPL lambda.

This oligonucleotide consists of 53 base pairs; the sense I strand is diagrammed in Figure 9. The synthetic oligonucleotide is designed so that translation of the N gene terminates at the TAA immediately upstream from the S/D sequence. In addition, the presence of KgnI and NcoI sites WO 89/02924 PCT/US88/03376 63 bracketing the S/D sequence allows for the facile insertion of short synthetic oligonucleotides in order to randomize the base sequence around the S/D sequence and obtain increased translation efficiency. In addition, the oligonucleotide specifies three restriction sites, namely, NcoI, StuI, and EcoRV, which allow for insertion of heterologous sequences in all three reading frames. The NcoI site encompasses the required ATG initiation codon, which can be supplied as a blunt end by filling out the cohesive Ncol end with Klenow enzyme in the presence of all four deoxynucleotides. Moreover, the sequence encodes translation stop codons in all three reading frames, so that predictable termini for fusion proteins are obtained.

Plasmid pPX1529 was obtained by ligating vector pPX1600 (after treatment with NcoI and filling out the cohesive ends with Klenow enzyme) to the 670 base pair XmnI fragment encoding the P. berghei CS protein repeat epitope and Regions I and II (Fig. 10). In addition, by treating the 670 base pair XmnI fragment with NruI, followed by purification and ligation of the resulting DNA fragment into the filled NcoI site of pPX1600, a plasmid (pPX1531) was obtained in which the codon for arginine (CGA), derived from the proper P. berqhei CS DNA sequence, was fused directly to an amino terminal methionine. Thus, no extraneous amino acids resulting from the translation of linker DNA, other than the initial methionine, was obtained. A seven amino acid carboxy terminal addition was obtained in this fusion, resulting from the translation of codons derived from the synthetic insert of pPX1600.

7.7. INSERTION OF EPITOPES OF P. FALCIPARUM AND P. BERGHEI INTO THE pPX1600 EXPRESSION VECTOR To express the CS repeat regions of either the rodent malaria parasite P. berqhei or the human malaria parasite P. falciparum at appropriately high levels in E. coli and Salmonella spp., synthetic complementary oligonucleotide F, -I WO 89/02924 PCT/US88/03376 64 strands were designed as diagrammed in Figure 11. The oligonucleotide encoding the P. falciparum repeat region was based on the consensus sequence ASN ALA ASN PRO (NANP) repeated four times. In addition, the oligonucleotide was designed so that asymmetrical Hinfl cohesive termini were formed at each end. By treating the annealed complementary strands with T4 polynucleotide kinase and T4 DNA ligase, head to tail polymerization of the repeated epitope was achieved. Creating blunt ends from the resulting single Hinfl cohesive ends and ligating the fragment into the blunt-ended NcoI site of pPX1600 resulted in a series of transformants of E. coli strain N99 cI+ containing the P. falciparum CS repeat epitope. (This strain of E. coli expresses the cI temperature-insensitive wild-type lambda repressor, and is lysogenic for bacteriophage lambda.) By 1 5 screening the transformants with appropriate restriction enzymes, clones having from one (monomer) to four (tetramer) copies of the P. falciparum oligonucleotides in the correct orientation with respect to the PL promoter were obtained. These plasmids were transformed into the E.

coli expression host N4830 (c1857), where expression of the epitope induced by temperature shift was confirmed by colony blot analysis and western blot analysis.

Concurrently, an oligonucleotide encoding two repeats of the P. berghei consensus octapeptide epitope (ASP PRO ALA PRO PRO ASN ALA ASN; DPAPPNAN) was synthesized. As described supra, two complementary strands were designed so that head to tail polymerization could occur upon ligation of annealed strands following treatment with T4 polynucleotide kinase and T4 DNA ligase. Ligated oligonucleotides were treated with Klenow enzyme in the presence of deoxynwcleotides and the resulting blunt-ended family of fragments were ligated to the filled-out NcoI site of pPX1600.

Transformant colonies were selected in E. coli N99 (cl+) and analyzed by restriction enzyme digestion. Monomeric to tWO 89/02924 PCT/US88/03376 tetrameric inserts were isolated and characterized further for expression of the immunodominant epitope by screening plasmids for induction following transformation into the E. coli expression host N4830.

To express the P. falciparum CS protein gene from a full length clone lacking only the sequence encoding the putative 16 amino acid signal sequence, a StuI-RsaI DNA fragment was cloned directly into the StuI site of plasmid pPX1600. The sequence data of Dame et al. (1984, Science 225:593) was used to establish'the CS protein reading frame within the restriction fragment and to predict the expression of the gene inserted into the StuI site of pPX1600. In this configuration, the full length mature gene is expressed from the PL promoter of the vector, and the initiating ATG (methionine) is that of the vector. The resulting plasmid was named pPX1534 and is diagrammed in Figure 12.

7.8. CONSTRUCTION OF VECTORS WHICH EXPRESS LT-B/CS FUSION PROTEINS, BY INSERTION OF SYNTHETIC OLIGONUCLEOTIDE REPEAT SEQUENCES 20 To construct plasmid vectors which encode fusions of the P. falciparum or P. berqhei immunodominant CS epitope to portions of the LT-B sequence, synthetic oligonucleotides encoding the epitope were ligated i (following filling out of the recessed 3 ends) into the 25 Clal site of pPX100 (Fig. The Clal site was filled out by the action of Klenow enzyme in order to maintain the reading frame of the CS protein. In particular, the oligonucleotide designed to encompass the P. falciparum repeated epitope is shown below with the translated amino 3 acid sequence below it: WO 89/02924 CT/US88/03376 66 GAT CCG AAC GCT AAC CCG AAC GCT AAC CCG AAC GCT 3 GGC TTG CGA TTG GGC TTG CGA TTG GGC TTG CGA Asp Pro [Asn Ala Asn Pro][Asn Ala Asn Pro][Asn Ala AAC CCG AAC GTT 3, TTG GGC TTG CAA Asn Pro][Asn Val This sequence includes three repeats of the consensus tetrapeptide [Asn-Ala-Asn-Pro]. This double-stranded oligonucleotide with sticky ends was blunted by Klenow enzyme and ligated into the Clal site of pPX100 to yield plasmid pPX1532, in which two 48-mer oligonucleotide units were cloned in-frame with the first 30 amino acids of LT-B, followed by out-of-frame reading of 28 amino acids derived from the LT-B gene sequence. The recombinant clones were isolated and the plasmid DNA characterized in E. coli strain JM103.

7.9. EXPRESSION OF CIRCUMSPOROZOITE PROTEIN EPITOPES IN E. COLI AND IN SALMONELLA SSP.

Plasmids were designed as described supra to express variants of the circumsporozoite epitopes of either P. falciparum or P. berghei. As described therein, the expression of these proteins or portions of these proteins, was designed to be controlled by several different promoter systems known to function and drive gene expression in E. coli. As such, plasmid constructions were first isolated and tested in commonly available laboratory strains of E. coli such as JM103, which is a suitable strain for studying control of gene expression controlled by the lac promoter and repressor, and such as N99 (cI and N4830 (cI857), which are suitable E. coli hosts for examining gene expression controlled by the PL promoter.

Because overexpression of gene products can often lead to deleterious effects on bacterial cell growth, control of gene expression can be important in obtaining the desired expression plasmid construction.

__11 i SWO 89/02924 PCT/US88/03376 67 After desired plasmids were obtained in suitable E.

coli hosts, plasmids carrying variants of the CS genes were transferred into several different species of Salmonella.

Expressing plasmids were transferred into either S. enteriditis serotype dublin (commonly known as S. dublin) SL1438 (ATCC Accession No. 39184), S. typhimurium SL3261, or into S. typhi Ty523 or Ty541. (Salmonella typhimurium strain SL1479, ATCC Accession No. 39183, and S. typhi strain Ty531, ATCC Accession No. 39926, are other strains readily available for use.) The attenuated mouse virulent strains '0 SL1438 and SL3261 carry a chromosomal deletion of the aroA gene (Hoiseth, S.K. and Stocker, B.A.D. 1981, Nature 291:238). The attenuated S. typhi strain Ty523 carries a chromosomal deletion of the aroA gene, and Ty541 carries an additional deletion of the purA gene. To test whether the chosen promoters function in each of the three host Salmonella strains, plasmids pPX1515, pPX1528, and pPX1601 were transformed into S. typhimurium LT-2, strain LB5010 (a non-restricting, transformable mutant), from which P22 phage lysates (Schmeiger, 1972, Mol. Gen. Genetics 119:75) were obtained to transduce each of the plasmids into the desired strain of Salmonella. Expression of the LT-B/CS fusion plasmids was examined in each of the bacterial cultures by the western technique of Section 6.10. As shown in Figure 15, expression of the fusion protein controlled by each promoter was obtained in each of the host Salmonella strains. Figure 15 shows that expression of the LT-B/CS fusion protein containing the P. berghei CS protein sequence, controlled by either the lac promoter, the tac promoter, or the lambda PL promoter, was observed in each of three attenuated Salmonella strains: SL3261, SL1438 and Ty523.

In addition, the expression of the P. falciparum CS protein repeat epitope fused to the first 30 amino acids of the mature LT-B protein was demonstrated (Fig. 16). Cell WO 89/02924 PCT/US88/033 7 6 WO 89/02924 68 extracts of the Salmonella strains SL3261, SL1438, and Ty523, carrying pPX1532, were analyzed by isoelectric focussing as described in Section 6.10. The P. falciparum epitope was shown to be expressed in each of the strains, by binding anti-CS protein monoclonal antibodies as described in Section 6.10.

8. EXAMPLE: VACCINATION AGAINST MALARIA WITH ATTENUATED RECOMBINANT SALMONELLA WHICH EXPRESS CS PEPTIDES As demonstrated in Section 7.9, the circumsporozoite proteins of either P. falciparum or P. berqhei can be expressed at significant levels in several different Salmonella species including S. dublin, S. typhi, and S.

typhimurium. The lac, tac, and PL promoters each is capable of driving the expression of LT-B/CS fusion proteins or portions of CS proteins. The immunodominant CS peptides encoded by synthetic oligonucleotides can be efficiently expressed when regulated by the PL promoter and translation initiation signals supplicd by the expression vector. To test the vaccine potential of each of the plasmid constructs in an animal model system, each of the Salmonella bacteria carrying plasmids expressing CS peptides was used to vaccinate mice.

8.1. IMMUNOGENICITY IN MICE OF RECOMBINANT SALMONELLA WHICH EXPRESS CS PEPTIDES The ability of recombinant Salmonella expressing CS peptides to elicit antibody against CS proteins was demonstrated by the detection of specific anti-CS antibodies in the sera of mice vaccinated with the recombinant bacteria. Six week old female C57B1/6 mice (Taconic labs) were used throughout this study. Log phase cultures of appropriate bacteria were washed three times in sterile phosphate-buffered saline (PBS), and resuspended to 108 cells per ml in PBS. Mice were divided into groups of 5-10 1. WO 89/02924 PCT/US88/03376 69 and injected intraperitoneally with 0.1 ml of the appropriate bacterial cell suspension (10 cells).

Alternatively, mice were inoculated orally with doses of 1010 recombinant bacteria on day 0, followed by a second dose of 1010 bacteria on day 3. Control groups received either Salmonella strains expressing LT-B proteins from recombinant plasmids, or Salmonella strains carrying pUC8 or pUC18 parental plasmids. Each mouse was bled before immunization, and sera was stored at -70"C for future analysis. Mice initially vaccinated by the i.p. route were bled again on week 4 and boosted with 10 bacteria i.p.

Mice which had been vaccinated orally were boosted on week 4 with 1010 bacteria, followed three days later with a second boosting dose. Serum samples were tested for the presence of anti-CS antibody and anti'-LT-B antibody, by use of an enzyme-linked immunoabsorbent assay (ELISA), as described in Section 6.12.

The actual OD (optical density) values of control and experimental sera at 1:160 dilution are presented in Figure 17. Titers were determined based on a cutoff OD corresponding to the mean OD of pre-immune sera plus 3 standard deviations. A four fold rise in titer from pre- to postimmune sera was considered significant. Salmonella dublin SL1438 carrying pPX1528 or pPX1601 plasmids induced significant anti-CS primary antibody response but no anti-LT-B antibody response; both plasmids express an LT-B/CS fusion protein. In contrast, pPX1527 in SL1438 (expressing the LT-B gene) stimulated anti-LT-B antibodies. A slightly higher anti-CS response was observed with pPX1601 in SL1438 (expressing the CS gene under the control of the PL promoter) than that with pPX1528 in SL1438 (expressing the CS gene under the control of the tac promoter), suggesting that a higher level of expression may be very critical to elicit greater antibody response in this system. Boostable response was observed for each of the plasmid construc- WO 89/02924 PCT/US88/03376 tions, with the highest titer being observed with the bacteria expressing the largest amount of CS protein or LT-B/CS fusion protein. Mice that had been vaccinated with Salmonella dublin SL1438 expressing LT-B/CS fusion protein driven by the lac promoter showed no significant response after either primary or secondary vaccination, suggesting that the expression level of the fusion protein was too low.

8.2. PROTECTION AGAINST PLASMODIUM INFECTION IN MICE AFTER IMMUNIZATION WITH RECOMBINANT SALMONELLA EXPRESSING CS PEPTIDES The efficacy of the recombinant Salmonella strains expressing CS proteins for use as vaccines was demonstrated in the mouse model system, by showing protection against Plasmodium infection in immunized mice upon sporozoite challenge. Although expression of the P. falciparum immunodominant epitope can be demonstrated in S. typhi and other Salmonella, mice cannot be infected with sporozoites of P. falciparum. To demonstrate the ability of recombinant Salmonella dublin SL1438 carrying LT-B/CS fusion protein-encoding plasmids or CS protein-encoding plasmids to elicit protection, mice previously vaccinated with recombinant Salmonella were challenged with either a low dose (1000/mouse) or a high dose (104/mouse) of P. berghei sporozoites, by tail vein injection. As a control, unvaccinated mice were also challenged.

S. dublin SL1438, carrying either plasmids pPX1528 (tac-promoted) or pPX1601 (PL-promoted) expressing the LT- B/CS fusion protein, or carrying pPX1529 expressing the immunodominant repeat region of the CS protein, are capable of eliciting a protective response. In control experiments, vaccination at week zero and boosting at week four with either 10 micrograms D-16-N-KLH (DPAPPNAN-KLH; Egan et al., 1987, Science 236:453) or with 10 micrograms of partially purified LT-B/CS fusion protein derived from t 1 i L -i 1- -i"I WO 89/02924 PCT/US88/03376 71 E. coli (strain N4830 containing pPX1601) elicits no protection. Although significant titers of anti-CS antibody are observed in these control groups, little protection against sporozoite challenge is seen.

Mice orally inoculated with 10 S. dublin (carrying pPX1601) or S. dublin control cells and boosted after 4 weeks with 101 0 of those same organisms, yere challenged at week 13. Eight days after challenge with 103 P. berghei sporozoites by tail vein injection, 4 out of 5 of the animals immunized with the control S. dublin cells exhibited patent blood stage parasitemia, whereas only 1 out of 5 of the animals immunized with S. dublin (carrying pPX1601) showed blood-stage parasites. Thus, 20% of the control animals escaped infection, whereas 80% of the immunized animals were protected.

Thus, attenuated live Salmonella are capable of delivering a sporozoite epitope to the immune system in such a manner as to elicit protective immunity not achieved by customary routes of vaccination.

9. DEPOSIT OF MICROORGANISMS The following bacterial strains, carrying the listed plasmids encoding a Plasmodium epitope, have been deposited with the American Type Culture Collection (ATCC), Rockville, MD, and have been assigned the indicated accession numbers: Bacterial Accession Strain Plasmid Number Salmonella typhi pPX1532: A plasmid which 67519 Ty523 expresses a fusion protein of the first thirty amino acids of LT-B followed by a dimer of four tetrapeptide repeats, each of the r. i .1 PCT/US88/03376 WO 89/02924 72 P. falciparum CS protein, fused to 28 amino acids read out-of-frame from the LT-B gene. This fusion protein is expressed from the lac promoter.

Salmonella enteritidis serotype dublin SL1438 pPX1528: A plasmid which 67521 expresses a fusion protein of the first thirty amino acids of LT-B at the aminoterminus followed by 223 amino acids of the P. berghei CS protein transcribed from the XmnI fragment of the CS protein gene, with 28 amino acids read out-of-frame from the LT-B gene at the carboxyterminus. This fusion protein is expressed from the tac promoter.

II Salmonella enteritidis serotype dublin SL1438 pPX1601: A plasmid which 67520 expresses a fusion protein of the first thirty amino acids of LT-B at the aminoterminus followed by 223 amino acids of the P. berghei CS protein transcribed from the XmnI fragment of the CS protein gene, with 28 amino acids read out-of-frame from the LT-B gene at the carboxyterminus. This fusion protein is expressed from the PL promoter.

r -i WO 89/02924 PCT/S88/03376 73 E. coli N99cI pPX1534: A plasmid which 67518 expresses the full-length P.

falciparum CS protein gene (lacking only the sequence encoding the putative 16 amino acid signal sequence). This protein is expressed from the PL promoter.

The present invention is not to be limited in scope by the microorganisms deposited since the deposited embodiment is intended as a single illustration of one aspect of the invention and any microorganisms which are functionally equivalent are within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

It is also to be understood that all base pair sizes given for nucleotides are approximate and are used for purposes of description, and figures which diagrammatically depict DNA sequences are not necessarily drawn to scale.

V

WO 89/02924 PCT/U588/03376 International Application No: PCT/

MICROORGANISMS

OpioalSoo I cnecio Ihth mcoogais efrrd oonPo, 75 20 Opioa See flcnncto wt te ierorahe efrrdto~ througho page 7 Jtedeon A. IDENTIFICATION Of DEPOSIT'II 1~ Salmonella typhi Ty523 Further deposits @to identified on en addiv~oni sh.If carry ing gpP X1532 Hae of depositary institution 4 American Type Culture Collection (ATCC) Address of depositary Inetitution (inciluding postal code and country) 12301 Parkiawn Drive Rockville, Maryland 20852 Oats of deposit I Accession Number September 30, 1987 67519 Il. ADDITIONAL INDICATIONS I Ileans blank If not applicable). Thin Informaion Is continued on s separhte altechod shoot 0i C. DESIGNATED STATES FOR WHICH INDICATIONS ARE MADE lit the Indications ore not for ail designated States) D. SEPARATE FURNISHING OF INDICATIONS 0 feave biank If not appiicabte) The InI cations listed belonw wilt be submitted to the tnfernationat Bugou Inter e (Specify the general nature of the Indication* eg,.

Accession Number of Deposit E. RIT 4 1e c-he st weecoived with the Intsrnational application when filied Ito be checked by the receiningi Omca) (Authorized Officer) The dote of receipt (Iront the applicant) by the International Buireau to Wes (Au horlt ed Officer) Form PCTIRO/134 (Januairy 19at) WO 89/02924 PCT/US88/03376 PCT FORM 134 continued Accession Number Deposited Microorganism Date of Deposit Salmonella enteritidis serotype dublin SL1438 carrying pPX1528 Salmonella enteritidis serotype dublin SL1438 carrying pPX1601 E. coli N99cI carrying pPX1534 67521 September 30, 1987 67520 September 30, 1987 67518 September 30, 1987 Depository Institution: American Type Culture Collection 12301 Parklawn Drive Rockville, Maryland 20852 A.1

Claims (71)

1. An attenuated enteroinvasive bacterium containi a recombinant DNA sequence which encodes an epitope of a malaria parasite which sequence can be expressed by the bacterium such that an immune response against the malarial parasite is generated by a host inoculated with the bacterium.

2. The recombinant bacterium of claim 1 in which the bacterium is of the genus Salmonella.

3. The recombinant bacterium of claim 2 in which the bacterium is a Salmonella typhi, Salmonella typhimurium, or Salmonella enteritidis.

4. The bacterium of claim 3 which is selected from :he group consisting of Ty21, Ty2la, Ty523; and Ty541. The recombinant bacterium of claim 3 in which the bacterium is a serotype dublin.

6. The recombinant bacterium of claim 1 or 2 in which the bacterium has a deletion of one or more gena, functional in aromatic compound biosynthesis.

7. The bacterium of claim 1 or 2 which covTprises a ga17 mutant.

8. The bacterium of claim 1 in which the epitope is that of a circumsporozoite protein antigen. SUBSTITUTE SHEET IPEA/US v~T oy I Rec'i P'CWTTO 2NOV 89

9. The bacterium of claim 2 in which the epitope is that of a circumsporozoite protein antigen. The bacterium of claim 3 in which the epitope is that of a circumsporozoite protein antigen,

11. The bacterium of claim 8 or 9 in which the eoitope comprises the repeat region of the circumsporozoize protein antigen.

12. The bacterium of claim 8 or 9 in which the ipitope is of Region I or Region II of the circumsp-r.ooite protein antigen.

13. The bacterium of claim 8 or 9 in which tho pitope comprises Region I of the circumsporozoite proti antigen.

14. The bacterium of claim 1 in which the epitope is expressed as part of a fusion protein. The bacterium of claim 2 in which the epitope is expressed as part of a fusion protein.

16. The bacteriua of claim a in which the epitope is expressed as part of a fusion protein.

17. The bacterium of claim 14 or 15 in which the fusion protein comprises the B subunit of the heat-lzbile enterotoxin of E. coli or a fragment thereof which yields an immunoactive fusion protein. SUBSTITUTrE SHEET IPEA/US i i I-- pc~U SS03376 Rcd Z.T3 42Vl9 2t8. The bac~terium of claim 16 in which the ffusion protein comprises the B subunit of the heat-la&cjle entezrotoxin of E. coli or a fragment thereof,

19. The bacterium of claim I. in which the DNA sequr; nca is expressed under the control of the lac operon promoter of E. coli, the tac promoter. thre leftwa~nd promoter of bacteriophaqe lambda, or the rightward promoter of bacteriophage lamibda. The bacterium of claim 1, 2, or 3 in which the malaria parasite is a Plasmodilam faiciparux.

21. The bacterium of claim 8 in which the mala.-ia parasite is a Plasmodium facj~rm

22. The bacterium ofe claim 21 in which the epitope comprises the amino acid sequence asn-a".a-asn-prc.

23. The bacterium of claix 9 in which the mktiaria parasite is a Plasmodium falciparum.

24. The bacterium of claim 23 in which the bacterit-in is a Salmonella typhi as deposited with the ATCC rnd assigned accession number 67519. The bacterium of claim 18 in which the malaria parasite is a Plasmodium falciparumn.

26. The bacterium of claim 1 or 2 in which the SUBSTITUE SHEET IPEA/US PCT/US /-03376 20Rc'dPC/7T ,9!,V6T1 parasite is a Plasmodium vivax.

27. The bacterium of claim 1 or 2 in which the naLatia parasite is a Plasmodium ovale. 28, The bacterium of claim 1 or 2 in which the malaria parasite is a Plasmodium malariae.

29. The bacterium of claim i or 2 in which the malaria parasite is a Plasmodium berghei. The bacterium of claim 8 in which the malaria parasite is a Plasmodium berghei.

31. The bacterium of claim 30 in which the opitope comprises the amino acid sequence asp-pro-ala-pro-pro-asn-ala-asn.

32. The bacterium of claim 9 in which the malaria parasite is a Plasmodium beraihei.

33. The bacterium of claim 32 in which the bacterium is a Salmonella enteritidis as deposited with the ATCC and assigned accession number 67521.

34. The bacterium of claim 32 in which the bacterixurm is a Salmonella enteritidis as deposited with the ATCC and assigned accession number 67520. The bacterium of claim 18 in which the malaria "I- ~a ~ne% u SUBSTITUTE SHEET IPEA/US PCT/US 0 3 37 6 Rec'd FCT/PTO "htn parasite is a Plasmadium berghei.

36. The bacterium of claim 1 or 2 in which the malaria parasite is a Plasmodium yoelii.

37. The bacterium of claim I or 2 in which the mazria parasite is a Plasmodium knowlesi.

38. The bacterium of cl.aim 1 or 2 in which the ialctrla parasite is a Plasmodium cynomoJgi,

39. A vaccine formulation comprising a bacterium~ of claim 1 in which the epitope is characteristic of the sprorzoite stage of the malariaparasite, an in~ which the bacterium is infectious without causing significant disease in a host to be vaccina..ted1. A vaccine formulation comprising a bacterium of claim I in which the epitope is char-acteristic of the erythrocytic stage of the malaria paraaita, and in which the bacterium is infectious withomit causing significant disease in a host to be vaccinated.

41. A vaccine formulation comprising a bactarium of claim 1 in which the epitepe is characteristic of the exoerythrocytic stage of the malaria parasite, and in which the bacteriuxo is infectious without causing significant disease in a host to be vaccinated. $UBSITUTE SHEET IPEA/US !T c~~ i l i .a l ii l i i -C I I i l j I i111 m.Eil mi i2 11 .11. i1 i- II. PCT/US S 0 3 7 6 Rec'd PC/IPTO 22NOV- 9 3 -8:

42. A vaccine formulation comprising a bacterium of claim i, 2, 3, 4, and 5, in which the ba;terium is infectious without causing significant disease in a host to be vaccinated.

43. A vaccine formulation comprising a bacterium of claim 6 in which the bacterium is infectious without causing significant disease in a host to bo vaccinated.

44. A vaccine formulation comprising a bactorium of claim 7 in which the bacterium is infectious without causing significant disease in a host to be vaccinated. A vaccine formulation comprising a bacterium of claim 8, 9, or 10 in which the bacterium i infectious without causing significant disease in a host to be vaccinated.

46. A vaccine formulation comprising a bacterium of claim 11 in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

47. A vaccine formulation comprising a bacterium off claim 12 in which the bacterium is infectious without causing significant disease in a host to be vaccinated. o i ~SUBSTITUTE SHEET S0' *IPEA/US 'PCT/US 8 03 3 7 6 Rc'd FCT/PTO 22 1 5v19S

48. A vaccine formulation comprising a bacterium of claim 13 in which the bacterium is infectious without causing significant disease in a host to 'a vaccinated.

49. A vaccine formulation comprising a bacterium of claim 14, 15, or 16 in which the bacterium is infectious without causing significant disease in a host to be vaccinated. A vaccine formulation comprising a bacterium of claim 17 in which the bacterium is infectious without causing significant disease in a host co be vaccinated,

51. A vaccine formulation comprising a bactecium of claim 18 in which the bacterium is infectious without causing significant disease in a host to b- vaccinated.

52. A vaccine formulation comprising a bacterium of claim 19 in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

53. A vaccine formulation comprising a bacterium of claim 20 in which the bacterium is infectious without causing significant disease in a hcst to bs vaccinated. SUBSTITUTE SHEET U> IPEA/US \'Ty O P/US 33/03376 Rec'd PCT/PTO 22NOV1 9 9

54. A vaccine formulation comprising a bacteriun of claim 21 or 22 in which the bacterium is infecticus without causing significant disease in a host to be vaccinated. A vaccine formulation comprising a bacterium of claim 23 or 24 in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

56. A vaccine formulation comprising a bacterium of claim 25 in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

57. A vaccine formulation comprising a bacterium of claim 26 in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

58. A vaccine formulation comprising a bacterium of claim 27 in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

59. A vaccine formulation comprising a bacterium of claim 26 in which the bacterium is infectious without causing significant disease in a host to be vaccinated. -A SUBSTITUTE SHEET SIPEA/US qT n PCT/US 8 /03376 Rec'd PCT/PTO 2 2 NOV9 A vaccine formulation comprising a bacteriu, of claim 29 in which the bacterium is infectious without causing significant disease in a host to b vaccinated,

61. A vaccine formulation comprising a bacterium of claim 30 or 31 in which the bacterium is infectiouLs without causing significant disease in a host to 'e vaccinated.

62. A vaccine formulation comprising a bacterium of claim 32, 33 or 34 in which the bacterium is infectious without causing significant dissase in a host to be vaccinated.

63. A vaccine formulation comprising a bacterium of claim 35 in which the bacterium is infectious without causing significant disease in a host to be vaccinated.

64. A vaccine formulation comprising a bacterium of claim 36 in which the bacterium is infectious without causing significant disease in a host to be vaccinated. A vaccine formulation comprising a bacterium of claim 37 in which the bacterium is infectious without causing significant disiase in a host to e vaccinated. SUBSTITUTE SHEET IPEA/US PCV/U 89/03376 Rec'd PCT/PTO 22NOV1 9 S9 A yvcina fo-muJlation comprising abceimo claim 38 in which the bacterium is infectious without oausing significant disease in a host to be vac.Lnated.

67. A v'ultivalent vaccine formnulation comprising a bacterium of claim I or 2 and a bacterium capable of epreossion of a second heterologous epitope, which bacteria are infectious without causing significant dis~ease in a~ h-ost to be vaocinated. A method for expressing an epitope of a r1alaria parasite, comprising: a) constructing an attenuated enteroinvasive bacterium ontaining a recombinant DNA sequence which encodes an apitope of -1 malaria parasite, which sequence can be expressed by the bacterium; andI b) allowing the bacterium to grow under conditions wThich induce the expression of the encoded epitcpe. 69, The method according to claim 68 in which the bacterium is a Salmonella. The method according to claim 69 in which the bacterium is a Salmonella typhi, Salmonella typhmuri=, or Salmonella enteritidis. ~N4~ ~,SUBSTITUTE SHEET IPEA/US ii~ III im liii I I ~iiii Iliplill iii II I II II p Rec'd PCT/PTO 2 2NOV 1 989 721, The mettod actcordirig to claim 68 or 69 in which the epitope is that of a circumsporozoite antigen. 72, rhi nehod according to claim 68 in which the DNA aequernce ise xpressed under the control of the lac opp-ron promoter of E, 'coli.

73. The method according to claim 69 in which the DNA saq-uonce is expressed under the control of the lac operon promater of E, coli.

74. The method according to claim 73 in which the bactorium is a Salmonella typhi as deposited with the ATC2C and aoi:igned accession number 67519. Tht method according to claim 68 in which the DNA sequonce is expressed under the control of the tac promoter. '76, Thia method according to claim 69 in which the DNA sequence is expressed under the control of the tao promoter.

77. Thq method according to claimJ~6 in which the bacterium is a SalmonellN&*i a deposited with the ATCC and assaigned accession number 67521.

78. The method according to claim 68 in which the DNA sequence is expressed under the control of the le~tward promoter of bacteriophage lambda. SUBSTITUTE SHEET I PEA/US Paius 8/O3376 Rec'd PCT/ PTO0 2 N 0V~ 7 9 The m~ethod accoirding to claim 69 in which the DNA seqen-e is ex-pressed under the control of the IP-e0tward promotar of bacteriophage lambda. M0 The method according to claim 79; in which the nar.terium is a Salmonella as deposited with the kTCC and assigned accession number 67520. 31. Tho mathod according to claim 68 or 69 in which the DNA seqence is expressed under the control of the right-ward promoter of bacteriophage lambda, 2.Tb't r.*thod according to cla3,7- 68 or 69 in which the mnalaria parasite is a Plasmodium talciparum. 83, The method according to claim 68 in which the mdlaria parasite Is a Pl'ismodium vivax.

84. The method according to claim 68 in which the malaria parasite is a Plasmodium ovale. The -method according to claim 68 in which the malaria parasite is a Plasmodium malariae.

86. Thl, mothod according to claim 68 or 69 in which the malaria parasits is a Plasmodium berghei.

87. The method according to claim 68 in which the malaria parasite is a Plasmodium yoelii. SUBSTITUT SHEET IPEA/US pct/S 8803 37 Rec'd PGT/PTO 2 2NOV 98

88. The method according to claim 68 in which the malaria parasite is a Plasmodium kn.o.wlesi. The mallhod according to claim 68 in which the M alaria parasite is a Plasmodium cynomlgi, An attenuated bacterium of the genus salmonella having an arOA or gal mutation and containing a r:ocombinant DNA sequence which encodes an epitope of a cizounsporozoit* protein antigen of a plasmodia. malarial. -parasite which sequence can be expressed such that an imniuna response against the malarial paraoite is genoirated in a host inoculated with the bacterium.

92.. An attenuated bacterium of claim 90, wherein the spitope is that of a circumsperozoite protein antigen. 31. An attenuated bacterium of claim 90, wherein the mal~arila3 parasite is a P. falciparum,

93. An attenuated bacterium of claim 90, wherein the malarial parasite is P. berqhei,

94. An attenuated bacterium of 90, wherein the epitope is expressed as part of a fusion protein. An attenuated bacterium of claim 94, wherein the fusion protein comprises the B subunit of the SUBSTITUTE SHEET IPEA/US NOW 89 heat-labile enterotoxin of E. coli. or fragment thereof which provides an immunoactive fusion protein.

96. An attenuated bacterium of claim 95, wherein the fusion protein comprises the N-terminal 30 amino acids of the B subunit of the heat-labile enterotoxin of E. coli.

97. An attenuated enteroinvasive bacterium containing a recombinant DNA sequence which encodes an epitope of a malaria parasite which sequence can be expressed by the bacterium such that an immune response against the malarial parasite is generated by a host inoculated with the bacterium, which bacterium is substantially as hereinbefore de cribed with reference to Example 7.

98. A vaccine formulation comprising a bacterium of claim 97 in which the epitope is characteristic of the sprorzoite stage of the malaria parasite, and in which the bacterium is infectious without 15 causing significant disease in a host to be vaccinated.

99. A method for expressing an epitope of a malaria parasite, which method is substantially as hereinbefore described with reference to Example 7.

100. An attenuated bacterium of the genus Salmonella having an aroA or 20 galE mutation and containing a recombinant DNA sequence which encodes an epitope of a circumsporozoite protein antigen of a plasmodial malarial parasite, which bacterium is substantially as S. hereinbefore described with reference to Example 7.

101. A method of constructing the DNA sequence contained within the enteroinvasive bacterium of claim 97, which method is substantially as hereinbefore described with reference to Example 7.

102. A method of constructing the DNA sequence contained within the enteroinvasive bacterium of claim 97, which method is substantially as hereinbefore described with reference to any one of Figures 7, 8 or 10 to 12.

103. A DNA sequence when prepared by the method of claim 101 or 102. DATED this TWENTY-FIRST day of AUGUST 1991 Praxis Biologics, Inc. Patent Attorneys for the Applicant R SPRUSON FERGUSON LMM/606Z d SUBSTITUTE SHEET I 1DEA/US r IWO 89/02924 PCT/US88/03376 Toq I Nru I hinc R AAf1T7"AC CCCT- ~CGA AATACAGTCA -AAGATTACT Xmn I i -C gene sequence AAAAAAATGA GAAAAAAAAC CACCACCAAA CCCAAATGAC CAAATGACCC ACCACCACCA CACCACCAAA CGCAAATGAC CAAATGACCC AGCACCACCA CACCACCAAA CGCAAATGAC GAAATAACAA TCCACAACCA CACAGCCACA GCCACAACCA ACAATAACAA AAATAATAAT AATTTGTTAA ACAGATCAGG GAAAAAATAG AGCGTAATAA CCACCACCAC AACGCAAATG CCAGCACCAC AACGCAAATG CCACCACCAC CAGCCACGGC CAGCCACGAC AATGACGATT GATAGTATCA CAAACCCAAA ACCCAGCACC CAAACGCAAA ACCCAGO ACC CAAACCCAAA CGCAGCCACA CACAGCCACA CTTATATOC CAGAGGAATG TGCCGATGCT TAAATTGAAA TGACCCACCA ACCAAACGCA TGAC CC AGOA ACCAAACGCA TG AC CCAGO A ACCACAGCCA ACCACAGOCA AAGCGCGGAA GTCTCAATGT 1/17 CCCGAAGGAA CAACCACCAC CC ACC A AACO AATGACCCAG CCACCAAACG AATGACCCAG CC ACOAC AAG CAGCCACAAC GGTGGT AAT A A AA ATACT AG A ACGT AAC AT GA AG ATTTG A SSpI ATATTTAT Xmn I GTGGTTCTGG TATAAGAGTT AGAAAACAA AGGTTCAAA CCTTAGAAGA TATTGATACT GAAATTTGTA AAATOGATAA Ss P1 TTGTAAGCAA TTCATTAGGA TTTGTA~AT TTTAGTATT SSIp Ss ACATTACGCA TGATTAT9A KTTTATATA TTATATNAKT GTGTAAACTT TATTTTTTTT ATTGTGAACT TTTCCTTATT GTATATATAT TTAATATGTA AATCAAAAGA AAAAATAAAT IATAATATAA ATTAAAAAAT AAAATATATA TGCATTACAA TTTTTTTCGT GTTTATTATA TATGTAGTTA ACTTGCTATG TAAGAAAGCA ATGTTCAAGT AGTATTCTTT AATTAAATAA *pI ATTTTACATA CATATGACGT TATTACGATT ATGTTTATAT AATAGAAGGC TTATTATATT AATTTACTTT TTTTAGTTTA Ymn I ACGATACGC9AAGGGGTE Nru I Taq I GAATT .1 FIG. I UM,0317'17UT& Z SHEIE-l" 1011mr I WO 89/02924 WO 8902924PCT/US88/03376 2/117 CGA AAT ACA GTC AAG AGA TTA CTT CX, GAT GGT CCC GAA GGA AAA AAA AAT GAG AAA AAA Arg Asn Thr Val Asn Arg Leu Leu Ala Asp Ala Pro Glu Gly Lys Lys Asn Giu Lys Lys AAC GAA AAA ATA GAG CGT AAT Asn Giu Lys Ile Giu Arg Asn AAT AAA TTG AAA CAA CCA GCA Asn Lys Leu Lys Gin Pro Pro R g o CCA CCA CCA AAC CGA AAT Pro Pro Pro Asn Pro Asn GAC ,A sp CCA CGA CCA CCA AAC CGA AAT][IGAC CCA CCA CCA CCA AAG CCA AAT1FGAC CCA CCA CCA Pro Pro Pro Pro Asn Pro AsfAsp Pro Pro Pro Pro Asn Pro AsnJ Asp Pro Pro Pro CCA AAC GCA AAT1[GAC GCA GGA CCA CCA Pro Asn Ala AnAsp PRo Ala Pro Pro AAC GGA AAT1FGAC Asn Aia AsjAsp CCA GGA CCA CGA AAG GCA AAT1 Pro Ala Pro Pro Asn Ala Asn] [GAG CCA GCA GCA CCA AAG GCA AAT [GAG CCA GCA CCA CCA AAG GGA AAT fGAC CCA GCA CCA Asp Pro Ala Pro Pro Asn Ala AnAsp Pro Ala Pro Pro Asn Ala Asnj Asp Pro Ala Pro GCA AAG GCA AAT1[GAC CCA GCA CCA GGA Pro Asn Ala AsjAsp Pro Ala Pro Pro AAC GGA AAT1EGAC Asn Ala Asnj[Asp CCA GCA CGA CCA AAC GCA AAT1 Pro Ala Pro Pro Asn Ala AsnJ GAC GCA GCA CCA CCA AAC CCA AAT GAC CGA GGA GCA GCA CAA GGA AAT AAC AAT [,CA CAAI Asp Pro Pro Pro Pro Asn Pro Asn Asp Pro Ala Pro Pro Gin Gly Asn Asn Asn Pro Gird [GGA GAG1 CA CGG1[GGG GAGI[CCA CAA GCA GAG CCA GAG] GGA GAAFCGA GAG1fGGA GAG] GGA CAA1 Pro GinJ r o AgPro Gin Pro Gin Pro Gin Pro Gin Pro Gin Pro Gin Pro Gin Pro Gin GGA GAG GGA GGA GCA GAG GGA CAA GGA GAG GCA GGT GOT AAT AAG AAT qXAC AAA AAT AAT Pro Gin Pro Arg Pro Gin Pro Gin Pro Gin Pro Gly Giy Asn Asn Asn Asn Lys Asn Asn AAT AAT GACG AT TGT TAT ATC GGA AGG GGG GAA AAA ATA GTA GAA TTT GTT AAA GAG ATG Asn Asn Asp Asp Ser Tyr Ile Pro Ser Ala Giu Lys Ile Leu Giu Phe Val Lys Gin Ile AGG GAT AGT ATG Arg Asp Ser Ile, GTT AGA AAA GGA Val Arg Lys Arg AGA GAG GAA TGG TGT CAA TGT AAG GTA ACA TGT GGT TCT Thr Giu Glu Trp Ser Gin Gys Asn Val Thr Cys Giy Ser AAA GGT TGA AAT AAG Lys Gly Ser Asn Lys Region II AAA GGA GAA, Lys Aia Giu TGA AGT ATA Ser Ser Ile GGT ATA AGA Gly Ile Arg GAT ATT GAT Asp Ile Asp GAT TTG ACC TTA GAA Asp Leu Thr Leu Giu ACT GAA ATT TGT AAA ATG OAT AAA TGT Thr Giu Ile Gys Lys Met Asp Lys Gys TTT AAT ATT GTA AGG AAT TGA TTA Phe Asn Ile Val Ser Asn Ser Leu TAA ATA AAG ATT AGG CAT GAT TAT GGA TTT GTA ATA TTA TTA GTA TTA GTA TTG TTT AAT Giy Phe Val Ie Leu Leu Val Leu Vai Phe Phe Asn AGA TAT TTA TAT ATT ATA TAA ATA TTT TAG ATA GAT ATG AGG TGT GTA AAG TTT ATT TTT FIG.2 SUBS n TU 514 :1 SUBSTITUTE SHEET 1PEA/US WO 89/02924 PCT/US88/03376 3/17 fEcoRI AAT TCG GGA TGA S/D TCT CTA TGT GCA Set' Leu Cys Ala ACA CAA ATA TAT Thr Gin Ile Tyr AGA GAA ATG GTT Ar'g Giu Met Val AGT CAA CAT ATA Set' Gin His Ile ACA TAT CTG ACC Thr Tyr Leu Thr TCA ATT GCG GCA Ser Ile Ala Ala ACC TAT ATA ACA TAG AGG ATG CAA F SIGNAL SEQUENCE ATT ATG AAT AAA GTA AAA TTT Met Asn Lys Vai Lys The SacIr-Mature LT-B CAC GGA 'GCT CCT CAG TCT ATT His Gly Ai21Pro Gin Se' Ile ACG ATA AAT GAC AAG ATA CTA Thr Ile Asn Asp Lys Ile Leu ATC ATT ACA TTT AAG AGC GGC Ile Ile Thr Phe Lys Set' Gly GAC TCC CAA AAA AAA GCC ATT Asp Ser Gin Lys Lys Ala Ile GAG ACC AAA ATT GAT AAA TTA Giu Thr Lys Ile Asp Lys Leu Spe I ATC AGT ATG GAA NCTAG TTT Ile Set' Met Giu Atsn ACT .ACT GTA CTT ATA CTA ATG TAC CGA TCC TTA AAC TGT AAC TTT ACG GCG Phe Tnt' Ala TGT TCG GAA Cys Set' Giu Cia I GALA TCG ATG Giu Set' Met CAG GTC GAA Gin Vai Giu AAG GAC ACA Lys Asp Tht' AAT. AAT AAA Asn Asn Lys GCA TGT CTA TTA CTA TCC Leu Leu Set' TAT CAC AAC Tyr His Asn GCA GGC AAA Ala Gly Lys Xma I GTC CCG GGC Vai Pt'o Gly TTA AGA ATC Leu At'g Ile ACC CCC AAT Thi' Pro Asn ATG CTA GGA AGC CTT ATG CTG CAT TTG AAA AGG CGG ACT ATA ACA GCT TCC ACT ACA GGG AGC Hind III GGG GGG GC 'GCT AGC TGT TAT AGC AAA CAG AAA AAA CTA FIG. 3 :JZZTMUTZ SHEET WO 89/02924 z pJC2i7 iclSalAc PROMOTE E4117 Eco-t EcoR i PPst pJC21H ncncSaalAccc loc BamHl PROMOTE Xmo ELIGAS EcoRI Hindditt laca PROMOTERco~ 1114 BASE PAIRS -S AATTCGAACCCCTTCG I Arg I':Am REPEAT REGION f k al TAT CGGAGGGGTTCG 0 7Nrur XmnI1 IL'NA. AgTRANSLATION 66! BASE PAIRS TERMINATION AA Ail pPXlOO CIaX dCTP i-dGTP pPX152O pPXI5I5 HindXJI lac ,PROMOTER Icc \1' PROMOTER jALN j ~j ~T 9// SUBSTITUTE SHEET IPEA/US WO 89/02924 PCT/US88/ 03376 6/117 JUlPU!H Iff POWH XlPU!H ladS ffT!H XJPU!H f IPUH Ivix 1704 3U!-I* IDWX ff3 UIH 130S 1803 V'. ~0 11041H 1d033 130s

18003- SUBSTITUTE SHEET I EcoRI inSad HHincl PROMOTE EcoRTHinc I Hind II Spel FIG.7 Hindincl EcoRI Sinai I.l Nqen e -S HpoI HpaI pPLX (PHARMACIA) f 1 -1 N GENE m 4.TRANSLATION m 1STOP TRANSLATION m CG GGA rA INITIA7T01N EcoRr Sad A HinclI BLUNT ENDS B3Y S LN ENZYME pPX 1601 Eco RI-NO HindIl dCTP Hnf Xal dGTP Xa HincIE dTTP XmafSel0 HincII HindKl Spel Spe Hin dil Hin dlU U 1~ SYNTHETIC OLIGONLICLEOTIfEII GGT ACC TAA CTA AGG AGG TTT ACC CAT GGA GGC CTT GAT ATC TGA ATG ACT GA Kpn NcoI Stul EcoRV SYNTHETIC SHINE! DALGARky) SEQUENCE FIG. 9 Hincff 681 BASE PAIR XmnI FRAGMENT NcoI kenow d CTP dATP dGTP dTTP psi pvujT Bol 11N" NruI XBanlL Banfl pPX 1600 I FAAT CCG AAC GGC TTG GC1FAAC CCG CGA!ITTG GGC AAC GCi!AAC CCG AAC GCT','FAAC CCG AAC GCGI. TTG CGA TTG GGC TTG CGAJLTrG GGC TTG CGCITTA %TG3 T 4 POLYNULCLEOTIOE KINASE T 4 LIGASE MONOMER DIMER z.N. MER 4KLENOW ENZYME dATP, (fTP FlG.11 Bair -1 A StIu REPEAT Stul Rsal FRAGMENT OF P FALCIPA RUM CS PROTEIN GENE SspI SSTOP -Rsor OLPL KpnI Ncol pPX1600 C--*Stuf C T /-Ec o R2 REPEAT REGION FIG.12 WO0 89/02924 PCT/US88/03376 13 /17 1 23 4 FIG. 13 SUBSTITUTE SHEET WO 89/02924 PCT/US88/03376 4 14 117 1 23 45 6 FIG. 14 ~7TUTZE SH EET WO 89/02924 PCT/US88/ 03376 I 0. a 0 co c C~J al aCa a a 15/117 4 3 2,4 K S. typhimuritirn S. dublin SL3261 SL1438 coa S, typhi TY523 FIG -TITUTE SHEV TY523 p U08 /SL1 438 pPX 1532/SL1,438 pPX1532/TY523 23 pU C8/tSL32 61 pPX1532/SL3261 ~.pPX 1532/JM 103 IPTG ~ppX 1532/JM1O3 IPTG tt +1 f 0.6- 0.4 00 w0 1601 1527 1601 f527 1601 1601 f527 CS (PBERGHEIJ RESPONSE ANTI LT-B RESPONSE n FIG. 17 INTERNATIONAL SEARCH REPORT International Application No. PCT/US8 8 /03376 1. CLASSIFICATION OF SUBJECT MATTER (if several classification symbols apply, indicate all) 6 According to International Patent Classification (IPC) or to both National Classiication and IPC IPC C12P 21/00; A61K 39/00; C07K 13/00 435/68; 424/88; 530/350 II. rICL:.L aAR.CHEDtif Minimum Documentation Searched 7 Classification System Classification Symbols U.S. 435/68, 70, 91, 172.1, 172.3, 320, 879 935/19, 27, 2q, 41, 47, 56, 65, 72 424/88 530/350 Documentation Searched other than Minimum Documentation to the Extent that such Documents are Included in the Fields Searched a Chemical Abstracts Data Base (CAS) 1967-1988 Keywords: Salmonella, Plasmodium,gal mutant,circumsporozoite, vaccine, heat labile toxin LT-B. immunogen III, DOCUMENTS CONSIDERED TO BE RELEVANT 9 Category Citation of Document, I1 with indication, where appropriate, of the relevant passages 12 Relevant to Claim No. 13 P,Y Science, Volume 240, issued April, 1988 1-89 (Washington, (SADOFF et al) "Oral Salmonella typhimurium vaccine expressing circumsporozoite protein protects against malaria", see abstract. Y Science, Volume 225, issued Auaust, 1-38,68-d9 1984 (Washington, U.S.A.) (DAME et al) "Structure of the gene encoding the immunodominant surface Santigen on the sporozoite of the human malaria parasite Plasmodium falciparum", see abstract. Y Science, Volume 230, issued November, 1-38,68-89 1985 (Washington, U.S.A.) (ARNOT et al) "Circumsporozoite protein of Plasmodium vivax: gene cloning and characterization of the immunodominant epitope", see abstract. SSpecial categories of cited documents: to later document published after the international filing date document defining the general state of the art which is not or priority date and not in conflict with the application but considered to be of particular relevance cited to understand the principle or theory underlying the invention earlier document but published on or after the international en of p r r te c d filing date document of particular relevance; the claimed invention cannot be considered novel or cannot be considered to document which may throw doubts on priority claim(s) or involve an inventive step which is cited to establish the publication date of another document o particular relevance; the claimed nvention citation or other speclal reason (as specified)Y" document of particular relevance the claimed invention Scannot be considered to involve an inventive step when the document referring to an oral disclosure, use, exhibition or document is combined with one or more other such docu- other means ments, such combination being obvious to a person skilled document published prior to the international filing date but in the art. later than the priority date claimed document member of the same patent family IV. CERTIFICATION Date of the Actual Completion of the International Search Date of Mailing of this international Search Report December 1988 6 FEB 1989 International Searching Authority Signature of Authorized Officer ISA/US JOAN ELLIS C-L Form PCTISA1210 (sond sheet (Rev.11-87) V 7 International Application No. PCT/US88/03376 Ill. DOCUMENTS CONSIDERED TO BE RELEVANT (CONTINUED FROM THE SECOND SHEET) Category Citation of Document, with indication, where appropriate, of the relevant passages IRelevant to Claim No Y Y,p Y, p Y Y Y YP yp Molecular and Cellular Biology, Volume 6, issued November 1986 (Washington, U.S.A.) (EICHINGER et al) "Circumsporozoite protein of Plasmodium berghei: gene cloning and identification of the immunodominant epitopes", see abstract. Infection and Immunity, Volume 44, issued May, 1984 (Washington, D.C., (KLIPSTEIN et al) "Properties of cross-linked toxoid vaccines made with hyperantigenic forms of synthetic Escherichia coli heat-stable toxin", see abstract and page 268. US, A, 4,411,888 (KLIPSTEIN et al) October 1983, see abstract. US, A, 4,751,064 (SELA et al) 14 June 1988, see abstract. US, A, 4,735,801 (STOCKER) April 1988, see abstract. Journal of Infectious Diseases, Volume 156, issued July, 1987 (Chicago, Illinois, U.S.A), (HONE et al) "Construction of defined galE mutants of Salmonella for use as vaccines", see abstract. Infection and Immunity, Volume 46, issued November, 1984 (Washington, (CLEMENTS et al) "Construction of a potential live oral bivalent vaccine for typhoid fever and cholera- Escherichia coli related diarrheas", see abstract. EP, 172107 Al (ANDERSON et al), 19 February 1986, see abstract. EP 249 449 Al (HONE et al), 16 December 1987, see abstract and page 1. L-38,68-89 39-67 -67 -67 9-67 39-67 -67 7,18 1-7,39-81 FormPCTISAN2IO extrashtl) (Rev.11-87)