AU2004200177B2 - Alpha(1,3)-Galactosyltransferase Negative Swine - Google Patents

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S&FRef: 354333D3

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Name and Address of Applicants: The University of London 30 Guilford Street London WC1N 1EH United Kingdom The General Hospital Corporation Fruit Street Boston Massachusetts 02114 United States of America Actual Inventor(s): Address for Service: Invention Title: Kenth T. Gustafsson David H. Sachs Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) a(1,3)-Galactosyltransferase Negative Swine The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c a 1.3) ACLCTOSYLT R AN SPERASE IMEOAT!V

SINE

Donor organ shortages have led to hopes that xenotransplantation could serve as an alternative means of organ availability. Swine, particularly mini-swine, are an attractive alternative to non-human primate donors because of potentially greater availability, the reduced risk of zoonotic infections, appropria size of organs and the reduced social and ethical concerns (Sachs, D.H. er al. 1976.

Transplantation 22:559-567; Auchincloss, H. 3r. 1988.

Transplantation 46:1-20). However, one of the major barriers to xenotransplantation is the phenomenon described as hyperacute rejection (Busch et al. 1972. Am. J. Pathology 79:31-57; Auchincloss, H. Jr. 1988. Transplantation 46:1- 2 0 This phenomenon describes a very rapid and severe humoral i rejection, which leads to destruction of the graft within minutes or hours of the transplant of the donor organ.

Hyperacute rejection is apparently mediated by a complex series of events, including activation of the complement systems, activation of blood coagulation proteins, activation of endothelial cells and release of inflammatory proteins (Busch ec al. 1972. Am. J. Pathology 79:31-57; Platt, J. L.

1992. ASAIO Journal 38:8-16). There is an accumulating body of information that implicates a group of pre-formed antibodies, the so-called natural antibodies, to be of -1fundamental importance in the hyperacute rejection seen in grafts between species- Species combinations in which the recipients of grafts have circulating antibodies that can initiate the hyperacute response to the donor species are described as discordant. Pigs and humans are one such discordant species combination.

The hyperacute rejection process is initiated when the natural antibodies of the recipient 'bind to cells of the donor organ (-I.att et al. 199.0. Transplantation 50:870-822; Platt et al. 1990. Inznunology Today 11:450-456). It has been suggested that porcine N-linked carbohydrates carrying a terminal Galcx1-3Ga1lft-4GICNAc structure are the major targets f or anti -swine xenoreactive human natural antibodies (Good et al. 1992. Transplantation Proceedings 24:559-562; Sandrin et al. 1993. Proc. Natl. Acad. Sci. USA 90:11391-11395). One major difference between the glycosylation pattern of swine tissues and human tissues is the presence of high levels of a terminal Galol-3Gal#1-4GlCNAC structure on swine cells and tissues. This structure is expressed at high levels in all lover mammnals investigated, but is poorly expressed on cells and tissues of Old World monkeys, apes and humans (catarrhines). (Galili. U. and Swanson, K. 1992. Proc. Natl.

Acad. Sci. USA 88:7401-7404; Galili et al. 1987. Proc. Natl.

Acad. Sci. USA. 84:1369-1373). A specific transf erase, UDP- ,a6 Gal:Galpl-->4GlcNAC al--:,3-galactosyltransf erase (EC 2.4.1.151; MUM,3 galactosyltransf erase) is responsible for the transfer of a terminal galactose to the terminal galactose residue of N-acetyllactosamine- :type carbohydrate chains and lactosaminoglycafls according to the reaction: 210 UDP-GaJ Gal~l-- 3.4GlcNAc-R ,Gal1--i3Gala-- .4GlcNAC-R

.UDP

where R may a glycopretein or a glycolipid (Blanken, w. M.

and Van den Bijinden, D. H. 1985. J. Biol. Chem. 260:12921- 12934). Thus the Gala1-3GalO1-4GlcNAc epitope. ,Full length cDNA sequences encoding the murine (Larsen et al. 1989. Proc.

Natl. Acad. Sci. USA. 86:8227-8231) and bovine (Joziasse et al., 1989. J. Biol. Chem. 264:14290-14297) enzymes have been determined. In addition, the genomic organization of the murine a 3) galactosyltralsf erase gene has been established (Joziasse et al. 1992. Biol. Chem. 267:.5534-5541)

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~o partial sequence encoding the 3' region of the porcine a(L.3) galactosyltransferase cDtNA gene has been determined (Dabkowski et al. 1993. Transplantation Proceedings. 25:2921) but the full lei.,,h sequence has not been reported. The absence of the 51 sequence is significant f or the S applications described herein. in contrast to the lower maimials, humans do not express the a(1,3) galactosyltralsferase. Furthermore, human sequences homologous to the murine sequence correspond to a processed pseudogene on chromnosome 12 and an inactivated remnant on ca chromosome 9 (Shaper et al. 1992. Genomics 12:613-615).

In accordance with the invention, swine organs or tissues or cells that do not express aC1, 3) galactosyltransferase will not produce carbohydrate moieties containing the distinctive terminal Galcul-3Galo1-4GcNAc a~epitope that is a significant factor in xenogeneic, particularly human, transpl ant rejection of swine grafts.

Further in accordance with the invention, is the aspect of diminishing the production* of a galactosyltraflsf erase to an extent suf ficient to prevent the amount produced f rom ~O providing carbohydrates with the Ga.cl1-3Gal1l-4GlcNAc epitope from being presented to the cell surface thereby rendering the transgenic animal, organ. tissue, cell or cell culture immunogenically tolerable to the intended recipient without -3- IN 4 requiring complete a(1,3) galactosyltransferase gene suppression.

One principal aspect of the present invention is that the inventors have isolated the Sentire porcine a(l,3) galactosyltransferase cDNA gene (SEQ. ID NO. The oo identification, isolation and sequencing of the entire cDNA gene, now particularly providing the sequence of the 5' end is an important advance because, as described in Example 2, this region has been identified as the most efficient for antisense targeting.

Moreover, as compared with mouse and bovine homologous sequences (Figure this Sregion of the a(1,3) galactosyltransferase mRNA appears to deviate extensively between C1 these species making it extremely unlikely that a use of "cross-species" antisense 0 10 constructs would be successful.

CN Accordingly, there is described herein an isolated nucleic acid having a sequence selected from the group consisting of SEQ. ID NOS: 1 and 13 through 24.

There is also described herein porcine cells, in vitro, said cells comprising a disrupted a(1,3)-galactosyltransferase gene encoding the polypeptide of SEQ ID NO: 1, whereby expression of functional a(1,3)-galactosyltransferase is inhibited.

There is also described herein a process for producing a modified porcine cell, the process comprising: treating a porcine cell, in vitro, said treating including introducing a disruption into the ac(1,3)-galactosyltransferase gene encoding the polypeptide of SEQ ID NO: 1, whereby expression of functional ac(1,3)-galactosyltransferase is inhibited.

There is also described herein a modified porcine cell produced by a process of the invention.

In an aspect of the present invention there is provided a product, comprising: porcine cells in which the normal expression of a(1,3) galactosyltransferase is inhibited, said cells including a galactosyltransferase gene encoding a polypeptide comprising the amino acid sequence of SEQ ID NO: 1, wherein said gene has been disrupted to inhibit normal expression of a(1,3) galactosyltransferase.

In a further aspect of the present invention there is provided a process for producing a porcine cell that normally does not express galactosyltransferase, the process comprising: disrupting in an isolated porcine cell a galactosyltransferase gene encoding a polypeptide comprising the sequence of SEQ ID NO: 1 by homologous recombination with DNA isogenic to said gene, said isogenic DNA including a mutation that disrupts said gene to prevent normal expression of galactosyltransferase.

[R:\LIBZZ]354333D3.doc:ake IN 4a 0 In a further aspect of the present invention there is provided a porcine cell produced by a process of the invention.

SAlso disclosed herein is a product, comprising: Sporcine cells in which the normal expression of a(1,3) galactosyltransferase is inhibited, said cells including a galactosyltransferase gene encoding a polypeptide comprising the amino acid sequence of SEQ ID NO: 1, wherein said gene has been disrupted to inhibit normal expression of galactosyltransferase.

SAlso disclosed herein is a process for producing a porcine cell that normally does C not express galactosyltransferase, the process comprising: 0 10 disrupting in a porcine cell a galactosyltransferase gene encoding a polypeptide N comprising the sequence of SEQ ID NO: 1 by homologous recombination with DNA isogenic to said gene, said isogenic DNA including a mutation that disrupts said gene to prevent normal expression of galactosyltransferase.

Another feature of the present invention relates to genetically altered animals, more specifically transgenic, chimeric or mosaic swine in which the expression of biologically active a(l,3) galactosyltransferase is prevented in at least one organ, tissue or cell type.

Transgenic animals carry a gene which has been introduced into the germline of the animal, or an ancestor of the animal, at an early developmental stage. The genetic alteration in transgenic animals is stably incorporated into the genome as a result of intentional experimental intervention. Typically, this results from the addition of exogenous foreign DNA or novel constructs (Palmiter et al. 1986. Ann. Rev. Genet.

20:465). With the advent of embryonic stem (ES) cells and specific gene targeting, the definition of transgenesis now includes specific modification of endogenous gene sequences by direct experimental manipulation and by stable incorporation of DNA that codes for effector molecules that modulate the expression of endogenous genes BZZ]354333D3.doc:ake

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(Gossler et al. 1986. Proc. Natl. Acad. Sci. USA. 83:906 5 Schwarzberg et al. 1989. Science 246:799; Joyner et al. 1989.

Nature 338:153).

One preferred approach for generating a transgenic animal involves micro-injection of naked DNA into a cell, preferentially into a pronucleus of an animal at an early embryonic stage (usually the zygote/one-cell stage). DNA injected as described integrates into the native genetic material of the embryo, and will faithfully be replicated O together with the chromosomal DNA of the host organism. This allows the transgene to be passed to all cells of the developing organism including the germ line. Transgene DNA that is transmitted to the germ line gives rise to transgenic offspring. If transmitted in a Mendelian fashion, half of the offspring will be transgenic. All transgenic animals derived from one founder animal are referred to as a transgenic line. If the injected transgene DNA integrates into chromosomal DNA at a stage later than the one cell embryo not all cells of the organism will be transgenic, and lo the animal is referred to as being genetically mosaic.

Genetically mosaic animals can be either germ line transmitters or non-transmitters. The general approach of microinjection of heterologous DNA constructs into early embryonic cells is usually restricted to the generation of 2 dominant effects, one allele of the transgene (hemizygous) causes expression of a phenotype (Palmiter et al. 1986. Ann. Rev. Genetics 20:465.) In another preferred approach, animals are genetically altered by embryonic stem (BS) cell-mediated tranagenesis (Gossler et al. 1986, Proc. Natl. Acad. Sci. USA. 83:9065).

ES cell lines are derived from early embryos, either from the inner cell mass (ICM) of a blastocyst (an embryo at a relatively early stage of development) or migrating primordial germ cells (POC) in the embryonic gonads. They have the potential to be cultured in vitro over many passages are conditionally immortalized) and they are pluripotent, or totipotent are capable of S differentiating and giving rise to all cell types. ES cells can be introduced into a recipient blastocyst which is transferred to the uterus of a foster mother for development to term. A recipient blastocyst injected with ES cells can develop into a chimeric animal, due to the contributions from the host embryo and the embryonic stem cells. ES cells can be transfected with heterologous gene constructions that may cause either dominant effects, inactivate whole genes or introduce subtle changes including point mutations.

Subsequent to clonal selection for defined genetic changes, a small number of ES cells can be reintroduced into recipient embryos (blastocysts or morulae) where they potentially differentiate into all tissues of the animal including the germ line and thus, give rise to stable lines of animals with designed genetic modifications. Totipotent porcine embryonic stem cells can be genetically altered to have a heterozygous mutant, preferably null mutant allele, particularly one produced by homologous recombination in such embryonic stem cells. Alternatively, gene targeting events by homologous recombination can be carried out at the same locus in two consecutive rounds yielding clones of cells that result in a homozygous mutant, preferably a null mutant (Ramirez-Solis et al. 1993. Methods in -nzymol. 225:855).

In one preferred embodiment of this invention a DNA sequence is integrated into the native genetic material of ?6 the swine and produces antisense RNA that binds to and prevents the translation of the native mRNA encoding a(1,3) galactosyltransferase in the transgenic swine.

In a particularly preferred embodiment the genome of the transgenic swine is modified to include a construct comprising a DNA complementary to that portion of the a (1,3) galactosyltransferase coding region that will prevent expression of all or part of the biologically active enzyme.

As the term is used "integrated antisense sequence" means a non-native nucleic acid sequence integrated into the genetic material of a cell that is transcribed (constitutively or inducibly) to produce an mRNA that is complementary to and capable of binding with an mRNA produced by the genetic material of the cell so as to regulate or inhibit the expression thereof.

In another embodiment of the invention, cells or cell lines from non-mutant swine are made with the a(1,3) galactosyltransferase inactivated on one or both alleles through the use of an integrated antisense sequence which binds to and prevents the translation of the native mRNA encoding the a(1.3) galactosyltransferase in said cells or cell lines. The integrated antisense sequence, such as the aO RNA sequence transcribed in Example 3 is delivered to the cells by various means such as electroporation, retroviral transduction or lipofection.

In another preferred embodiment, the transgenic swine is made to produce a ribozyme (catalytic RNA) that cleaves the a(1,3) galactosyltransferase mRnA with specificity.

Ribozymes are specific domains of RNA which have enzymatic activity, either acting as an enzyme on other RNA molecules or acting intramolecularly in reactions such as self-splicing or self-cleaving (Long, D.M. and Uhlenbeck, O.C. 1993. FASEB Journal. 7:25-30). Certain ribozymes contain a small structural domain generally of only about 30 nucleotides called a "hammerhead". The hammerhead is a loop of RNA that is flanked by two linear domains that are specific complements to domains on the substrate to be cleaved. The site on the hammerhead ribozyme that effects the cleavage of substrate is the base of the stem loop or hamerhead. As shown in Figure 3, the ribozymes of the present invention have flanking sequences complementary to domains near the 51 end of the a(1,3) galactosyltransferase cDNA gene.

The DNA for the ribozymes is integrated into the genetic material. of an animal, tissue or cell and is transcribed (constitutively or inducibly) to produce a ribozyue which is to. capable of selectively binding with and cleaving the at(1,3) galactosyltransferase mRNA. As it is a catalytic molecule, each such ribozyne is capable of cleaving multiple substrate molecules.

The catalytic "stem loop" of the ribozynie is flanked by 1S sequences complementary to regions of the a(1,3) galactosyltralsf erase mP.NA. In a particularly preferred embodiment the transgenic swine is modified to integrate a construct comprising the DNA coding f or -that portion of catalytic RNA necessary to inactivate the m1MI of the ce(1, 3) galactosyltrans ferase operably linked to a promoter theref or.

In another embodiment of the Invention, cells or cell lines from non-mutant swine are made with the a (1,3) galactosyltransf erase inactivated on one or both alleles through the use of an integrated ribozyme sequence which Sbinds to and cleaves the native PmRA encoding the ra(1,3) galactosyltransf erase in said cells or cell lines. The integrated ribozyme sequence, such as the RNIA sequence transcribed in Example 4 is delivered to the cells by various means such as electroporation, retrovIral transduction or lipofection.

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In another preferred embodiment, using cultured porcine embryonic stem cells, a mutation, preferably a null mutation is introduced by gene targeting at the native genomic locus encoding a(1,3) galactosyltransferase. Gene targeting by homologous recombination in ES cells is performed using constructs containing extensive sequence homology to the native gene, but specific mutations at positions in the gene which are critical for generating a biologically active protein. Therefore, mutations can be located in regions important for either translation, transcription or those coding for functional domains of the protein. Selection for ES clones that have homologously recombined a gene targeting construct, also termed gene 'knock out" construct, can be achieved using specific marker genes. The standard procedure \S is to use a combination of two drug selectable markers including one for positive selection (survival in the presence of drug, if marker is expressed) and one for negative selection (killing in the presence of the drug, if marker is expressed) (Mansour et al., 1988. Nature 336:348) One preferred type of targeting vector includes the neomycin phosphotransferase (neo) gene for positive selection in the drug G418, as well as the Herpes Simplex Virus-thymidine kinase (HSV-tk) gene for selective killing in gancyclovir.

Drug selection in G418 and gancyclovir, also termed positive negative selection (PNS) (Mansour et al. 1988. Nature 336:348; Tubulewicz et al. 1991. Cell 65:1153) allows for enrichment of BS cell clones that have undergone gene targeting, rather than random integration events.

Confirmation of homologous recombination events is performed LO using Southern analysis.

The design of the a(l,3) galactosyltransferase targeting construct is described in Example 6. The procedure as applied here uses a positive selection (survival) based on integration of the neo (neomycin resistance), preferably in

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inverse orientation to the endogenous a (1,3) galactosyltransferase gene locus in a cassette with the phosphoglycerate kinase (PGK-1) promoter and with flanking oligonucleotides complementary to two separate regions of the a(1,3) galactosyltransferase gene sequence. It is understood that other positive selectable markers may be used instead of neo. The neo gene is linked with its promoter to be under control thereof. Downstream from the second flanking sequence is the HSV-tk gene which, if integrated into the' genome encodes for production of thymidine kinase making the cell susceptible to killing by gancyclovir (negative selection). The integration of the neo gene but not the HSVtk gene occurs only where integration into the a(1,3) galactosyltransferase gene has occurred and provides for both positive and negative selection of the cells so transformed.

In another preferred embodiment, using isogenic DNA, it has become possible to achieve high frequency homologous recombination even in biological systems, such as zygotes, which do not lend themselves to the use of elaborate selection protocols and were, therefore, previously not suitable candidates for the isolation of cells which showed positive marker attributes indicating homologous recombination. This use of targeting vectors which include isogenic DNA which is substantially identical to that of 2S6 chromosomal segments of Lhe target recipient cell, can be used to target zygotes which thereafter develop into transgenic animals. The use of these zygote cells is preferably to produce a mutation, preferably a null mutation, at the chromosomal locus encoding a (1,3) 2O galactosyltransferese. Thus, these vectors contain extensive sequence homology to the native gene, but also contain specific mutations at segments in the gene which are critical for generating a biologically active protein. Therefore, mutations can be located in regions important for either

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translation, transcription, or those coating for functional domains of the protein. The high percentage of homologous recombination achieved using isogenic DNA makes it possible to avoid the need for selection of clones that have homologously recombined the gene targeting construct, as described above with respect to the "knock out" embodiment thereby making it possible to avoid the need for the standard selection procedure described above.

More particularly, in this embodiment, PCR is used to AO identify and extract 1-2 kb DNA fragments, which are then subjected to restriction fragment length polymorphism digestions to identify areas or alleles that are most abundantly present in the line of mini-swine selected for zygote injection. Known insertion vectors are used, however, \V replacement vectors also described in the art could also be used. It is also possible to use DNA sequences with an isogenic replacement vector that require only a few kilobases of uninterrupted isogenic DNA. As such, it is possible to effect highly efficient homologous recombination such that it is not necessary to screen targeting vector recombined zygotes. Rather, genomic DNA screening using PCR can be done after the piglets are born. These transgenic founder animals, which are observed to have the transgene targeted to the native a galactosyltransferese locus that are heterozygous null mutant for that gene, are grown and interbred to produce animals that are homozygous null mutant for this locus, resulting in the knock out of the a (1,3) galactosyltransferese gene which can be confirmed by antibody or lectin binding assays.

The swine is preferably an a(1,3) galactosyltransferase negative swine grown from a porcine oocyte whose pronuclear material has been removed and into which has been introduced a totipotent porcine embryonic stem cell using. protocols for -11-

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nuclear transfer (Prather et al. 1989, Biol. Reprod. 41:414) ES cells used for nuclear transfer are negative for the expression of at(1,3) galactosyl transferase, or alternatively, totipotent ES cells used for nuclear transfer are mutated in a targeted fashion in at least one allele of the a(1,3) galactosyltransferase gene.

The swine is preferably lacking expression of the a(1,3) galactosyltransf erase gene and bred from chimeric animals which were generated from ES cells by blastocyst injection or \O morula aggregation. ES cells used to generate the preferably null-mutated chimeric animal were mutated at least in one allele of the a(1,3) galactosyltransferase gene locus, using gene targeting by homologous recombination.

A chimeric swine is preferably constituted by ES cells \S mutated in one allele of the a(1,3) galactosyltransferase gene. Derived from mutated ES cells are also germ cells, male or female gametes that allow the mutation to be passed to offspring, and allow for breeding of heterozygous mutant sibling pigs to yield animals homozygous mutant at the a(1,3) xo galactosyltransferase locus. Also described is a swine, deficient for an a(l,3) galactosyltransferase protein characterized by lack of expression of a(1,3) galactosyltransferase protein) and have little, if any, functional Galal-3GalOl-4GlcNAc epitope-containing 1- carbohydrate antigen on the cell surface are produced.

Further described are methods of producing transgenic swine and methods of producing tissue from heterozygous swine or homozygous swine of the present invention. The present invention also relates to cell lines, such as swine cell lines, in which the a(1,3) galactosyltransferase gene is inactivated on one or both alleles and use of such cell lines as a source of tissue and cells for transplantation.

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Tissues, organs and purified or substantially pure cells obtained from transgenic swine, more specifically from hemizygous, heterozygous or homozygous mutant animals of the present invention can be used for xenogeneic transplantation into other mammals including humans in which tissues, organs or cells are needed. The a galactosyltransferase inactive cells can themselves be the treatment or therapeutic/clinical product. For example, keratinocytes rendered a(1,3) galactosyltransferase inactive can be used tO for macular degeneration and pancreatic cells rendered a(1,3) galactosyltransferase deficient can be used to replace or restore pancreatic products and functions to a recipient. In another embodiment, a(1,3) galactosyltransferase inactive cells produced by the present method are further manipulated, using known methods, to introduce a gene or genes of interest, which encode(s) a product(s), such as a therapeutic product, to be provided to a recipient. In this embodiment, the a(1,3) galactosyltransferase deficient tissue, organ or cells serve as a delivery vehicle for the encoded product(s).

For example, a(1,3) galactosyltransferase deficient cells, such as fibroblasts or endothelial cells, can be transfected with a gene encoding a therapeutic product, such as cytokines that augment donor tissue engraftment, Factor VIII, Factor IX, erythropoietin, insulin, human major histocompatibility (MHC) molecules or growth hormone, and introduced into an individual in need of the encoded product.

Alternatively, recipient blastocysts are injected or morulae are aggregated with totipotent embryonic stem cells yielding chimeric swine containing at least one allele of a mutated, preferably null-mutated a 3) galactosyltransferase gene produced by homologous recombination. A chimeric swine is preferably constituted by ES cells mutated in one allele of the a(l,3) galactosyltransferase gene. Derived from mutated ES cells are also germ cells that allow the mutation -13-

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14 to be passed to offspring, and breeding of heterozygous mutant sibling pigs to yield animals homozygous mutant at the a(1,3) galactosyltransferase locus. Also described is a swine, deficient for an a(1,3) galactosyltransferase protein characterized by essentially no expression of a(1,3) galactosyltransferase protein) and with little, if any, functional Galxl-3Galpl-4GlcNAc epitope-containing carbohydrate antigen on the cell surface are produced. Further described are methods of producing transgenic swine and methods of producing tissue from heterozygous swine or homozygous swine of the present invention. The present invention also relates to cell lines, such as swine cell lines, in which the a(1,3) galactosyltransferase gene is inactivated on one or both alleles and use of such cell lines as a source of tissue, organs and cells for transplantation.

In the context of this specification, the term "comprising" means "at least" or "including principally, but not necessarily solely". Furthermore, variations of the word "comprising" such as "comprise" and "comprises", having correspondingly varied meanings.

Figure 1 illustrates the complete cDNA sequence of the a(1,3) galactosyltransferase gene (SEQ. ID. No. having an open reading frame of 1113 base pairs, encoding a 371 amino acid protein.

Figure 2 compares the protein sequences encoded by the porcine, bovine and murine a(1,3) galactosyltransferase cDNA genes.

Figure 3 illustrates the secondary structure of a transacting hammerhead ribozyme targeted to galactosyltransferase mRNA.

Figure 4 illustrates the genomic organization of the murine galactosyltransferase gene. Exoms are labeled 1-9 and are indicated by solid boxes.

Intron sequences are represented by a thin line.

[1:\DayLib\LIBVV]04336.doc:sxc A method of producing a chimneric swine and porcine organs and tissue cultures, homozygous for an a(1,3) galactosyltransf erase gene inactivation, in which ar(1,3) galactosyltransf erase protein synthesis and cell surface GalaiI-3Gal0Il-4GlcNAc epitope-coltailifg carbohydrate cell surface markers expression are deficient is disclosed. Of particular interest are purified cell types which have been rendered deficient in a(1,3) galactosyltrafferase expression. Such cell types incl 'ude fibroblasts, 13 keratinocyteS, iyoblasts and endothelial cells.

in one embodiment of the present invention, swine cells altered as described herein are used to provide cells needed by a recipient or to provide gene therapy. The cells, which are deficient in Galux(l-3)Gal0l-4GldIAc epitope -containling carbohydrates cell surface antigen, are cultured and transplanted to an oocyte.

The embryonic stem cells with the null mutant ar(1,3) galactosyltraflaferase locus are introduced into swine blastocySts, which are then introduced into a pseudopregnant swine. The embryo develops into a chimneric swine offspring.

When bred with wild-type females, chimeric males transmit the a galactosyltralsf erase inactivation in the embryonic stem cell to their offspring, which are heterozygous for the inactivation. Swine heterozygous for the a(1,.3) d_ galactosyltransferale gene inactivation can be intercrossed to produce swine homozygous f or the mutation.

Purified or substantially pure a(k,3) galactosyltralsf erase deficient cells can be obtained from tissues or tran~sgeflic or chimeric swine produced as described herein. Alternatively, they can be obtained from a normal (nan-altered) donor swi.ne and altered using a method descriL .d herein. These cells can be then cultured by known -ismethods to produce a quantity of cells useful for transplantation. In addition. cell lines, such as swine cell lines, in whiLch the av(1,3) galactosyltransf erase gene is disrupted, preferably on both alleles, are useful as a source of tissue and cells for transplantation.

EXAMPLE 1 ISOLATION AMD cKARAcTERIZATION OF PORCINE a(1,3) GL&CrosyLTRANSFERASS eDNA A previously 'described XZAP II porcine spleen cDNA LOlibrary (Gustafsson et al. 1990. Proc. Natl. Acad. Sci. USA.

87:9798-9802) was screened by hybridization with a cloned a(1,3) galactosyltransf erase cDHA probe (Joziasse et al.

1989. J. Biol. Chem. 264:14290-14297) The Genbank Accession number for the bovine at(l,3) galactosyltransf erase cDNA sequence is J04989. The bovine a(1,3) galactosyltransf erase cDNA probe was kindly provided by Dr. David Joziasse, University of Leiden, The Netherlands. The probe was radioactively labeled with a 32 P-dATP using. the Megaprime DNA labeling system (Amershaza International, UK). Positive -02 clones were confirmed by the polymerase chain reaction (PCR).

using primers (SRO. ID. NO: 2 and SEQ. ID. NO: 3) derived from the bovine a(1,3) galactosyltralsf erase cDNA sequence.

SEQ. ID. No.: 2 corresponds to bovine galactolyltransf erase nucleotides 712-729 and SEQ. ID. NO: 3 Lk corresponds to the reverse complement of bovine a(1.3) galactosyl trans ferase nucleotides 1501-1508. Recombinant p~luescript plasmids from positive clones were automatically excised with the helper phage R408 (Stratagene Ltd., Cambridgei UK) and amplified in S. call strain TG1 (ATCC 1,O 39078). Plasmid DNA was prepared using the Magic Miniprep kit (Promega Ltd., Southampton, UK) following the manufacturer' s instruct ions and the DNA was characterized by cleavage with BcoRI. DNA, sequencing was performed by the -16dideoxy chain ternuiZation method, using a T7 DNA polymerase sequencing kit (pharmacia BiosysteMS Ltd., Milton Keynes, UK) according to the manufacturer's instructions. The synthetic oligonucleocide primers SEQ. ID. NOS. 4-12 were used. SEQ.

~ID. NO. 4 is Stratagele SK, catalog number 300305, (Stratagene Inc., La Jolla, CA) SEQ. ID. NO: 5 corresponds to the reverse complement of porcine a (1,3) galactasyltransf erase nucleotides 94-111. SEQ. ID, NO: 6 corresponds to the porcine q(1,3) galactosyltransf erase nucleotides 163-180. SEQ. ID. NO: 7 corresponds to the reverse complement of porcine a(1,3) galactosyltransferase nucleotides 442-459. SEQ. ID. NO.- 8 corresponds to the complement of porcine and bovine a 3) galactosyltransferase nucleotides 538-555 and 982-999, respectively. SEQ. ID. NO: 9 corresponds to the reverse complement of porcine a(1,3) galactosyltransferale nucleotides 596-615. SEQ. ID. NO: corresponds to the porcine galactosyltransf erase nucleotides 682-699. SEQ. ID. NO: 11 corresponds to the porcine a(1,3) galactosyltransferase nucleotides 847-864.

SEQ. ID. NO: 12 corresponds to the reverse complement of porcine a(1,3) galactosyltransferase nucleotides 970-987.

Four positive clones were obtained from approximately 2 x 10' plaques. screened by hybridization with the bovine a 3) galactosyl trans ferase cDNA probe (Joziasse et al. 1989. J.

Biol.- Chem. 264-14290-14297). Three of these clones were confirmed to be positive by PCIL. Each of the' three recombinant pBluencript plasinida, generated by automatic excision f ram XZapII with helper phage. contained inserts of approximately 2.5 kb am determined by EcoRI cleavage. One clone, designated pSa13GT1, was selected for further study.

DNA sequence analysis of pSal13GTl revealed an open reading f rame of 1113 bases (See SEQ. ID. NO: 1 and Figure 1) showing 86% identity with the published bovine cDNA sequence -17- (Joziasse et a2!. 1989. J. Biol. Chem. 2C4:14290-14297) and encoding a 371 amino acid protein with 85% and 76% identity with the bovine and murine a galactosyl trans ferase amino acid sequences, respectively (Figure 2).

S EXAXPLE 2 A2NTISENSE OLIGONUCLEOTIDE UISIITION OF a( .3) EXPRESS IO Three antisense 5' and 3' phospkothioate -protected oligonucleot ides (S-oligonucleotides, SEQ. ID. N0s 13-15) are I C tested in an in vitro system employing porcine primary endothelial cell cultures (f romt porcine aorta) and a porcine B-cell line (L231, European Collection of Animal Cell Cultures, PHLS, Center for Applied Microbiology and Research, Porton Down, Salisbury, UK). SEQ. ID. NO: 13 corresponds to the reverse complement of porcine a(1,3) galactosyltransferase cDNA nucleotides 16-35. SEQ. ID. NO: 14 corresponds to the reverse complement of porcine a(1.3) galactosyltransferase cDNA nucleotides 31-53. SEQ. ID. NO: corresponds to the reverse comrplement-of porcine a (1,3) galactosyltralsf erase cMUL nucleotides 6-23. All three antisense oligonucleotides are directed at the 51 region of the iIaM surrounding the initiation of translation. Nonsense S -oligonucleot ides randomized from the antisense sequence are used as controls at similar molar concentrations.

Porcine endothelial cells are derived from miniature swine aorta by scraping the luminal surface of the blood vessel, as described (Ryan. et al. Tissue and Cell 12:-619-635).

The cells are suspended in M199 medium supplemented with fetal bovine serum (GIECO EEL. Gaithersburg, ND) and ~o gentamycin and plated in 25 cm! tissue culture flasks, precoated with fibronectin (5 psg/cm?) and laminin (1 pg/cm 2 Endothelial cell growth. suppement .(Collaborative Research, -18- Bedford, MA) at 150 pg/n] is added at the beginning of the culture. The cultures are maintained by changing one half of the medium every 2-3 days. The porcine lymphoblastoid cell line L231 is maintained in DMEM, 10% fetal bovine serum, 19 NCrC-109, 1% glutamine, It pen-strep (all from GIECO ERL, Gaithersburg, MD) and 5 x 10-2 M 2-mercaptoethanol (Sigma, St.

Louis, The L231 cells are sub-cultured by splitting the" cells 1:3 every three days.

For cell treatment, S-oligonucleotides are added, to a final concentration of 5-10 IpM, to growing cells at 24 hr intervals, typically for 48 hr. and then the treated cells are examined for the levels of a(1,3) galactosyltransf erase mRNA (by Northern blot analysis) and expression of the epitope on the cell surface by human AB serum and FITC- Slabeled mouse anti-human secondary reagents (anti-human IgM and IgG) EXAMPLE 3- PREPARATION AJIM USE OF IRTEGRATED A2ITISENSE CONSTRUCTS We are studying the ability of integrated antisense Sconstructs to inhibit specifically the production of the porcine gAlactosyltransf erase. Specific inhibition of the a(1,3) galactosyltransferase in transfected cells allows assessment of the contribution of the enzyme in the hyperacute phenomenon. Vectors are constructed to express a(1,3) galactosyltransf erase antisense mRNA, under the control of the cytomegalovirus (CMV) promoter. Specifically, pSal3GTI is cleaved with NotI and BcoRV which generates a restriction fragment of length 537 bp,, containing part of the paluescript polylinicer sequence through to nucleotide S31 of the a(1,3) galactosyltransf erase cDNA sequence. This DNA fragment is cloned into the exp~ression vector pcDNA3 (Invitrogen, San Diego, CA), cleaved with the same enzymes.

-19- The resulting vector therefore contains the porcine a(1,3) galactosyltransferase sequence in the antisense direction, relative to the OCV promoter located in pcDNA3. The construct is transfected, using electroporation or other high efficiency methods for introducing DNA into mammalian cells, into both porcine endothelial cells and the L231 porcine lymphoblastoid cell lines (grown as described in Example 2).

The effect of the antisense RNA is monitored by both Northern blot analysis of mRNA of the a(1,3) galactosyltransf erase iO gene and the degree of binding of human serum components natural antibodies).

EXARPLE 4 RIBOZYME SEQUENCES TEAT IRACTIVATE PORCINE a(1.3) GALACTOSYLTRANSFERASE mRxA (C This example describes a method for construction of the vectors which encode ribozyme sequences which are specifically designed to cleave the porcine a(1,3) galactosyltransferase mRNA sequence.

The design of the ribozyme sequences is based upon the consensus cis-acting hammerhead ribozyme sequence (Ruffner et al. 1990. Biochemistry 29:10695-10702). We used the Zuker algorithm in the suite of programs available from the Genetics Computer Group (Mad.lson, WI.) to model the cisacting hammerhead ribozyme sequences (Denman, R.B. 1993.

aS BioTechniquee 15:1090-1095). Ribozyme target sequences are identified within the a(1,3) galactosyltransferase mRNA sequence. A ribozyme sequence file for each potential ribozyme sequence is generated based on the target sequence and using five nucleotides to connect the mRNA target 2O sequence with the catalytic strand of the ribozyme. The sequence file is then folded into the lowest energy structure using RNAFOLD. Sequences which have non-ribozyme structures are discarded. Figure 3 illustrates one of the ribozymetarget RNA secondary structures, using the ribozyme corresponding to SEQ. ID. NO. 16. The small arrow indicates the cleavage site on the uiRNA, between stem I and stem III.

Synthetic oligonucleotides to encode the ribozymes (SEQ.

ID. Nos. 16-21) are made on an Applied BioSystems oligonucleotide synthesizer (Foster City, CA) with termini corresponding to the overhangs of the restriction endonucleases NotI and XbaI. The duplex DNAL is cloned into the maimmalian expression cloning vector pcDXA3 (Invitrogen, CA). Expression of the ribozyme is under the control of the 04V promoter present in pcDNA3. The transcripts consist of approximately 140 nucleotides both S' and 31 to the ribozyme sequence. The expressio'n level of the transcribed sequence is ascertained by Northern blot analysis. If the RNlA level Is low additional sequences will be included in the construct in order to generate a longer and more stable transcript.

The construct is transfected using the electroporation technique into porcine primary endothelial cells, porcine B DD cells ML231). Also, the vector is co-transfected with plasutid expressing the porcine a(1.3) galactosyltransferaSe iLnto' COS7 cells. Since COS7 cells do not express an endogenous a(1,3) galactosyltralsf erase, the effect of the presence of the ribozyme on the expression of the introduced Sporcine a(1,3) galactosyltransf erase gene is easily ascertained.

TuANsGWlIC SWINE PRODCW MISERszSE OR uxuozYKE RNlA TEA IEUTAU(.3) GALACTOSYLTR.ANSFERASE SYNTRrES!S This approach requires direct microinjection of transgene DNA into one of the pronuclei of a porcine embryo -21-

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at the zygote stage(one-cell embryo). Injected one-cell embryos are transferred to recipient foster gilts for development to term (Hammer et al. 1985, Nature 315:680; pursel et al. 1989, Science 244:1281) Critical to successfully accomplishing this approach is the age and weight of the donor pigs, preferentially the haplotype specific mini-swine. Optimally, the animals are of age 8 to 10 months and weigh 70 to G5 lbs. This increases the probability of obtaining adequate supply of one-cell embryos for microinjection of the transgenes. In order to allow for accurate timing of the embryo collections at that stage from a number of embryo donors, the gilts are synchronized using a preparation of synthetic progesterone (Regumate). Hormone implants are applied to designated gilts S1 30 days prior to the date of embryo collection. Twenty days later, ten days prior to the date of collection, the implants are removed and the animals are treated with additional hormones to induce superovulation i.e. to increase the number of embryos for microinjection. Three days following implant a) removal, the animals are treated with 400 to 1000 IU of pregnant mare serum gonadotropin (PMSG) and with 750 IU of human chorionic gonadotropin (hCG) three to four days later.

These animals are bred by artificial insemination (AI) on two consecutive days following injection of hCG.

Embryo collections are performed as follows: three days following the initial injection of hCG, the animals are anesthetized with an intramuscular injection of Telazol (3 mg/lb.), Rompum (2 mg/lb.) and Atropine (1 mg/lb.). A midline laparotomy is performed and the reproductive tract exteriorized. Collection of the zygotes is performed by cannulating the ampulla of the oviduct and flushing the oviduct with 10 to 15 ml phosphate buffered saline, prewarmed to 39* C. Following the collection, the donor animals are -22-

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prepared for recovery from surgery according to USDA guidelines. Animals used twice for embryo collections are euthanized according to USDA guidelines.

Injection of the transgene DNA into the pronuclei of the C- zygotes is carried out as follows. Zygotes are maintained in HAM's F-12 medium supplemented with 10% fetal calf serum at 38" C in 5 CO, atmosphere. For injection the zygotes are placed into modified BMOC-2 medium containing HEPES salts (Ebert et al. 1984. J. Embryol. Exp. Morph. 84:91-103), O1 centrifuged at 13,000 x g to partition the embryonic lipids and visualize the pronuclei. The embryos are placed in an injection chamber (depression slide) containing the same medium overlaid with light paraffin oil. Microinjection is performed on a Nikon Diaphot inverted-microscope equipped with Nomarski optics and Narishlige micro-manipulators. Using lens power the embryos are held in place with a holding pipette and injected with a glass needle which is backfilled with the solution of DNA containing the transgene (2 3/ml). Injection of approximately 2 picoliters of the AO solution (4 femptograms of DNA) which is equivalent to around 500 copies of the transgene is monitored by the swelling of the pronucleus by about 50%. Embryos that are injected are placed into the incubator prior to transfer to recipient animals.

O Recipient animals ale prepared similar to the donor animals, but not superovulated. Prior to the transfer of the injected embryos, recipient gilts are anesthetized, the abdomen opened surgically by applying a longitudinal, incision and the ovaries exteriorized. The oviduct ipsilateral to the ovary with the larger number of corpus lutei is flushed, the embryos checked to evaluate if the animals is reproductively sound. Approximately 4 to 6 zygotes injected with the transgene are transferred to the flushed oviduct, the -23abdominal incision sutured and the animals placed in a warm area for recovery. The status of the pregnancy is monitored by ultrasound starting at day 25, or approximately one week following the expected date of implantation. Pregnant 6- recipients are housed separately until they are due to f arrow- Newborn piglets are analyzed for integration of the transgene into chromosomal DNA. Genomic DNA is extracted from an ear punch or a blood sample and initial screening is 1O performed using PCR. Animals that are potentially transgenepositive are confirmed by Southern analysis. Transgenic founder animals are subjected to further analysis including the levels of expression, phenotype and germ line transmission. Northern analysis from RNA of selective 19 tissues including endothelial cells is performed to determine the level of transgene expression. Also, imnmunological assays including flow cytometric analysis for binding of antibody from human serum and complement mediated lysis of pig cells recognized by human natural antibodies are carried 2 out to evaluate the transgene effect. Animals that satisfy the above criteria are used as founders for breeding of a transgenic line. If the founder transgenic animals only satisfy part of the requirements, breeding and specific intercrossing of transgenic offspring is performed to assay the transgene effect in homozygous animals.

EXAMPLE 6 A SWINE MDE NULL-MOTANT FOR a(1.3) CALACrOSYLT ANS PASE BY HOMOLOGOUS RECOM AT ION USING PORCINE EMRYONIC STEM CELLS 0 Gene targeting by homologous recombination in swine requires several components, including the following: a mutant gene targeting construct including the -24-

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positive/negative drug-selectable marker genes (Tubulewicz et al. 1991. Cell 65:1153); embryonic stem cell cultures; and the experimental embryology to reconstitute an animal from the cultured cells.

The targeting construct is provided from a genomic clone that spans most of the a(1,3) galactosyltransferase gene and is isolated from a library made of isogenic DNA from a major histocompatibility complex (MHC) haplotype d/d of the miniature swine. Fragments of that genomic clone are iD introduced into a positive/negative selectable marker cassette specifically developed for gene targeting in embryonic stem (ES) cells and termed pPNT (Tubulewicz et al.

1991. Cell 65:1153). This gene targeting cassette includes as positive selectable marker the bacterial neomycin pI phosphotransferase gene (neo) which allows for selection of cells in G418. The neo gene is regulated by a promoter that guarantees high level expression in BS cells such as the phosphoglycerate kinase promoter-1 (PGK-1). Negative selection is accomplished by expressing the Herpes Simplex J Virus thymidine kinase (HSV-tk) gene which allows for selective killing of cells in Gancyclovir. Similar to the neo gene, the HSV-tk gene is regulated by the PGK-1 promoter, as well. In the targeting cassette pPNT there are unique and convenient cloning sites between the neo and the HSV-tk gene which are suitable sites to introduce the genomic fragment of the a(1,3) galactosyltransferase gene upstream of the translation initiation signal AUG SalI sites in introns 2 and 4) This fragment of approximately 2 kb of DNA is cloned in reverse orientation to the direction of transcription of t0 the PGK-neo cassette to assure that no truncated or residual peptide is generated at the a(1,3) galactosyltransferaselocus. Genomic sequences of the a(1,3) galactosyltransferase locus downstream of exon 4, approximately 5 kb are introduced into pPNT at the 5'-end of the neo gene. This targeting

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construction termed pPNT-alpha GT1 is linearized and transfected by electroporation into porcine ES cells. Double selection in G418 (150 to 300 pg/ml) and Gancyclovir is performed to initially isolate clones of ES cells with targeted mutations in the a(1,3) galactosyltransferase locus.

Confirmation of homologous recombinant clones is achieved using Southern analysis.

ES cell clones that have undergone targeted mutagenesis of one allele of the a(l,3) galactosyltransferase locus are r0 subjected to a second round of in vitro mutagenesis or used for reconstituting an animal that contains the mutation. A second round of in vitro mutagenesis can be carried out using an analogous targeting construction with hygromycin phosphotransferase hyg as positive selectable marker gene.

i( As far as the reconstitution of animals is concerned, the methods include nuclear transfer, blastocyst injection or morula aggregation. The preferred routes include either blastocyst injection or morula aggregation which yield chimeras between the donor cells and the recipient embryos.

Jo For both these methods recipient embryos are prepared as follows: embryo donor/recipient gilts are synchronized and mated as described in Example 5. On day 6 following artificial insemination or natural mating, the gilts are prepared for surgery as described earlier, anesthetized and the uteri retrogradely flushed using a prewarmed (38" C) solution of phosphate buffered saline (PBS). Intact blastocysts that are encapsulated by the zona pellucida are placed in a depression slide containing HEPES-buffered medium (Whitten's or TL-HEPES) and approximately 15 to 20 ES cells O0 are injected into the blastocoel using a glass injection needle with an opening of 20 pim and Narishige micromanipulators. Injected embryos are then reimplanted into recipient foster gilts for development to term and -26-

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pregnancies are monitored using ultrasound. Offspring is analyzed for chimerism -sing the polymerase chain reaction (PCR) of DNA samples extracted from blood, skin and tissue biopsies and primers complementary to .e neo or hyg gene.

Germ line transmission of the chimeras is assayed using PCR and in situ hybridization of tissue samples obtain from male and female gonads. Male and female chimeras which transmit the ES cell genotype to the germ line are crossed to yield homozygously mutant animals. Analysis of mutant animals for 1O expression of a(1,3) galactosyltransferase and binding of human natural antibodies to endothelial cells of those animals is used as final test to assess the validity of gene knock out approach in swine.

EXAMPLE 7 \f A SWINE MADE NULL-MUTANT FOR a(1,31 GALACTOSYLTPRASPERASE USING ISOGENIC DNA TARGETING INTO ZYGOTES Isogenic DNA or DNA that is substantially identical in sequence between the targeting vector and target DNA in the .2 chromosomes greatly increases the frequency for homologous recombination events and thus the gene targeting efficiency.

Using isogenic DNA-targeting vectors, targeting frequencies of 80% or higher are achieved in mouse embryonic stem cells.

In contrast, non-isogenic DNA-vector; normally yield targeting frequencies of around 0.5% to i.e., approximately two orders of magnitude lower than isogenic DNA vectors. Surprisingly, isogenic DNA constructions are predominantly integrated into chromosomes by homologous recombination rather than random integration. As a consequence, targeted mutagenesis of genes can, therefore, be carried out in biological systems, including animals and even zygotes, which do not lend themselves to the use of elaborate selection protocols.

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The significance for isogenic DNA in gene targeting approaches was first described by TeRiele et al., PNAS 89, 5128-5132 (1992) and also in PCT/US 92/07184.

In or^er for the isogenic DNA approach to be feasible, T targeting veL.ors have to be constructed from a source of DNA that is identical to the DNA of the organism to be targeted.

Ideally, isogeic DNA targeting is carried out in inbred strains of animals in which all genetic loci are homozygous.

All animals of that strain can therefore serve as a source for generating isogenic targeting vectors. In cases in which inbred strains of animals are lacking, genetic loci can consist of many different alleles. Thus, isogenic vectors can only be derived from the individual in which targeted gene replacement is attempted. Furthermore, the targeting vector would be isogenic for one allele only.

In the haplotype specific miniature swine, isogenic gene targeting vectors are readily derived for the MHC locus, since that genomic region has been maintained homozygous for several generations. Since the cDNA sequence to a (1,3) )ro galactosyltransferase locus has been determined (Example 1) and genomic clones have been generated recently it is now possible to map and thereby avoid, polymorphisms within the a galactosyltransferase locus gene.

Mapping of polymorphism is carried out as follows. A group of mini-swine that are closely related, either siblings and/or parent/offspring is identified. High molecular weight DNA is extracted and PCR reactions are set up to amplify sequences from Exon 6 to Exon 7 spanning Intron 6. The organization of Exons 5 through 9 of the porcine gene are known to be homologous to those of the murine gene (Figure 4, Joziasse, Shaper, Kim, Van den Eijnden, D.

and Joel H. Shaper, J. Biol. Chem. 167, pp. 5534-5541 -28-

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(1992)). In Figure 4, genomic organization of the murine a galactosyltransferase gene Exons are labeled 1-9 and are indicated by solid boxes. Intron sequences are represented by a thin line. The 5'-oligo in Exon 6 has the following sequence: TCC GAG CTG GTT TAA CAA TGG GTA -3' (SEQ ID NO: 25) and the 3' oligo in Exon 7 contains the following sequence: TCT TCG TGG TAA CTG TGA GTC CTA -3' (SEQ ID NO: 26). The PCR fragments are approximately 1 and 2 kb long. In order to assay for PCR-RLPs, restriction digestions using 4-cutters are carried out which are expected to cut frequently. Such 4-cutters include BstU I (CGCG), Hae III (GGCC), Hha I (GCGC) Sau3A (GATC), Rsa I (GTAC) and Taq I (TCGA), which are commercially available from New England BioLabs (Beverley, MA). Based on the pattern of restriction ig fragments obtained from parental animals and offspring, as well as between siblings, it is possible to define the number of different alleles present in that group of animals. In case the PCR-RFLP does not yield obvious sequence polymorphisms between different alleles in different animals, aO alternative methods can be employed including DNA sequencing or enzyme mismatch cleavage (EMC) using T7 or T4 resolvases.

Additional animals are then analyzed in a similar manner to identify specific alleles at the a 1,3 galactosyltransferase locus. Once several alleles have been identified, targeting constructions are prepared for those alleles that are most abundantly present in the line of mini-swine selected for zygote injection.

Gene targeting constructions are generated as follows.

A genomic library is made in lambda replacement vectors CO including Lambda FIX II, Lambda EMBL4 or Lambda Dash II (Stratagene Cloning Systems). The library is then plated at a density of around 50,000 plaques/15 cm plate and screened with a probe specific for Bxon 9 of the swine a (1,3) galactosyltransferase gene. The probe is generated using PCR -29which is carried out using a standard protocol: 35 cycles, anneal at 60OC for 20 sec, extend at 720C for 40 sec and denature at 940C for 20 sec. Positive clones with insert sizes of around 15 kb are then subcloned into plasmid vectors including pSP72 and engineered for targeting as either an insertion vector or a replacement vector.

An insertion vector is designed Ps described by Hasty and Bradley (Gene Targeting Vectors for Mammalian Cells, in Gene Targeting: A Practical Approach, ed, Alexandra L.

1O Joyner, IRL Press 1993). Insertion vectors require for only one crossover to occur for integration by homologous recombination into the native locus-. The double strand breaks, the two ends of the vector which are known to be highly recombinogenic, are located on adjacent sequences on the chromosome. Preferably the site of integration of the insertion vector is at the beginning of Intron 8 of the galactosyltransferase gene. The entire length of Intron 6 is thereby included as a homologous and identical sequence, carrying the minimal number mismatches. Exon 9 which encodes the catalytic domain ot the enzyme is then substituted by a selectable marker such as the neomycin phosphotransferase gene, or a derivative thereof ter-med IRES 6geo. Downstream, or 3' of the selectable marker, sequences from Intron 7, Exon 8 and Intron S are included, terminating at the site adjacent to the beginning of the vector. The targeting frequencies of that construction are in the range of 30 to 50%. All these constructions are made using standard cloning procedures.

The replacement vectors have also been extensively ,O described by Hasty ana Bradley, supra. Conceptually more straightforward than the insertion vector, replacement vectors issued here are essentially co-linear fragments of a certain stretch of genomic sequence at the a (1,3)

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galactosyltransferase locus. Preferably, the DNA sequence from which an isogenic replacement vector is constructed include approximately 6 to 10 kb of uninterrupted DNA. This DNA corresponds to a region between the start of Exon 4 and the end of Intron 8 of certain alleles of the a (1,3) galactosyltransferase locus from mini-swine. Exon 9, encoding the catalytic domain is replaced with the selectable marker gene, such as the neo gene, or a functional analog thereof. The 3'-end of the replacement vector includes the IO 3' untranslated region of the gene in Bxon 9, including approximately 1kb of isogenic DNA. Two crossovers, one on either side of the selectable marker causes the mutant targeting vector to become integrated and replace the wildtype gene.

Microinjection of the isogenic transgene DNA into one of the pronuclei of a porcine embryo at the zygote stage (onecell embryo), particularly the mini-swine, is accomplished by modification of the protocol described earlier. (Hammer et al. 1985, Nature 315, 680; Pursel et al 1989, Science 244, O 1281). Optimally, the mini-swine are of age 8 to 10 months and weigh 70 to 85 lbs. This increases the probability of obtaining an adequate supply of one-cell embryo donors. The gilts are synchronized using a preparation of synthetic progesterone (Regumate). Hormone implants are applied to a-S designated gilts 30 days prior to the date of embryo collection. Twenty days later, ten days prior to the date of collection, the implants are removed and the animals are treated with additional hormones to induce superovulation, to increase the number of embryos for microinjection.

C0 Three days following implant removal, the animals are treated with 400 to 1000 IU of pregnant mare serum gonadotropin (PMSG) and with 750 IU of human chorionic gonadotropin (hCG) three to four days later. These animals are bred by -31artificial insemination (AI) on two consecutive days following injection of hCG.

Embryo collections are performed as follows. Three days following the initial injection of hCG, the animals are anesthetized with an intramuscular injection of Telazol (3 mg/lb), Rompum (2 mg/lb) and Atropine (1 mg/lb). A midline laparotomy is performed and the reproductive tract exteriorized. Collection of the zygotes is performed by cannulating the ampulla of the oviduct and flushing the iO oviduct with 10 to 15 ml phosphate buffered saline, prewarmed to 390C. Following the collection, the donor animals are prepared for recovery from surgery according to USDA guidelines. Animals used twice for embryo collections are euthanized according to USDA guidelines.

Injection of the transgene DNA into the pronuclei of the zygotes is carried out as summarized below. Zygotes are maintained in HAM P-12 medium supplemented with 10% fetal calf serum at 380C in 5% CO, atmosphere. For injection the zygotes are placed into BMOC-2 medium, centrifuged at 13,000 0 g to partition the embryonic lipids and visualize the pronuclei. The embryos are placed in an injection chamber (depression slide) containing the same medium overlaid with light paraffin oil. Microinjection is performed on a Nikon Diaphot inverted-microsc .e equipped with Nomarski optics and S Narishige micromanipulators. Using 40x lens power the embryos are held in place with a holding pipette and injected with a glass needle which is back-filled with the solution of DNA containing the transgene (2 Injection of approximately 2 picoliters of the solution (4 femptograms of O DNA) which is equivalent to around 500 copies of the transgene is monitored by the swelling of the pronucleus by about 50%. Embryos that are injected are placed into the incubator prior to transfer to recipient animals.

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Recipient animals are prepared similar to the donor animals, but not superovulated. Prior to the transfer of the injected embryos, recipient gilts are anesthetized, the abdomen opened surgically by applying a longitudinal incision and the ovaries exteriorized. The oviduct ipsilateral to the ovary with the larger number of corpus lutei is flushed and the embryos are checked to evaluate if the animal is reproductively sound. Approximately 4 to 6 zygotes injected with the transgene are transferred to the flushed oviduct, the abdominal incision sutured and the animals placed in a warm area for recovery. The status of the pregnancy is monitored by ultrasound starting at day 25, or approximately one week following the expected date of implantation.

Pregnant recipients are housed separately until they are due to farrow.

Newborn piglets are analyzed for integration of the transgene into chromosomal DNA. Genomic DNA is extracted from an ear punch or a blood sample and initial screening is performed using PCR. Animals that are potentially transgene- .o positive are confirmed by Southern analysis. Transgenic founder animals are subjected to further analysis regarding the locus of transgene integration using Southern analysis.

Those animals that have the transgene targeted to the native a galactosyltransferase locus, that are heterozygous mutant for that gene. are grown up and bred to additional heterozygous mutant founder animals. Applying Mendelian genetics allows us to breed animals that are homozygous mutant for the a galactosyltransferase.

Functional assays using the lectin BI4 and human preformed 3 natural antibodies are then used to look at expression of the Gal a Gal epitope on swine cells and to confirm the knockout of the a galactosyltransferase gene.

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Claims (4)

1. A product, comprising: porcine cells in which the normal expression of c(1,3) galactosyltransferase is QQ inhibited, said cells including a galactosyltransferase gene encoding a polypeptide comprising the amino acid sequence of SEQ ID NO: 1, wherein said gene has been disrupted to inhibit normal expression of a(1,3) galactosyltransferase. U'-

2. The product of claim 1 wherein said gene includes an inactivating mutation Sproduced by homologous recombination with DNA isogenic to said gene, said DNA CN including a mutation that inactivates said gene to prevent normal expression of S 10 ca(1,3) galactosyltransferase. N1

3. The product of claim 1 or 2 wherein the product comprises a swine organ.

4. A process for producing a porcine cell that normally does not express galactosyltransferase, the process comprising: disrupting in an isolated porcine cell a galactosyltransferase gene encoding a polypeptide comprising the sequence of SEQ ID NO: 1 by homologous recombination with DNA isogenic to said gene, said isogenic DNA including a mutation that disrupts said gene to prevent normal expression of galactosyltransferase. A porcine cell produced by the process of claim 4. Dated 7 August, 2006 The University of London The General Hospital Corporation Biotransplant, Inc. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON R:\LIBZZ]354333 D3.doc:ake