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  • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
  • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
  • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
  • G01N33/569—Immunoassay; Biospecific binding assay; Materials therefor for microorganisms, e.g. protozoa, bacteria, viruses
  • G01N33/56983—Viruses
  • G01N33/56988—HIV or HTLV
• • C—CHEMISTRY; METALLURGY
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  • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
  • C07K14/005—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from viruses
  • C07K14/08—RNA viruses
  • C07K14/15—Retroviridae, e.g. bovine leukaemia virus, feline leukaemia virus human T-cell leukaemia-lymphoma virus
• • G—PHYSICS
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  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
  • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
  • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
  • G01N33/569—Immunoassay; Biospecific binding assay; Materials therefor for microorganisms, e.g. protozoa, bacteria, viruses
  • G01N33/56983—Viruses
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  • C07K2319/00—Fusion polypeptide
  • C07K2319/35—Fusion polypeptide containing a fusion for enhanced stability/folding during expression, e.g. fusions with chaperones or thioredoxin
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  • C12N2740/00—Reverse transcribing RNA viruses
  • C12N2740/00011—Details
  • C12N2740/10011—Retroviridae
  • C12N2740/14011—Deltaretrovirus, e.g. bovine leukeamia virus
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  • C12N2740/00—Reverse transcribing RNA viruses
  • C12N2740/00011—Details
  • C12N2740/10011—Retroviridae
  • C12N2740/14011—Deltaretrovirus, e.g. bovine leukeamia virus
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  • C12N2740/00—Reverse transcribing RNA viruses
  • C12N2740/00011—Details
  • C12N2740/10011—Retroviridae
  • C12N2740/14011—Deltaretrovirus, e.g. bovine leukeamia virus
  • C12N2740/14051—Methods of production or purification of viral material
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2333/00—Assays involving biological materials from specific organisms or of a specific nature
  • G01N2333/005—Assays involving biological materials from specific organisms or of a specific nature from viruses
  • G01N2333/08—RNA viruses
  • G01N2333/15—Retroviridae, e.g. bovine leukaemia virus, feline leukaemia virus, feline leukaemia virus, human T-cell leukaemia-lymphoma virus
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2469/00—Immunoassays for the detection of microorganisms
  • G01N2469/20—Detection of antibodies in sample from host which are directed against antigens from microorganisms
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
  • Y02A50/30—Against vector-borne diseases, e.g. mosquito-borne, fly-borne, tick-borne or waterborne diseases whose impact is exacerbated by climate change

Definitions

• HTLV-I Human T-cell lymphotropic virus
• HTLV-I Human T-cell lymphotropic virus
• HTLV-II shares approximately 70% genetic homology (translating into 80-95 % structural similarity at the protein level) with HTLV-I.
• the pathogenic potential of HTLV-II is not yet completely elucidated but HTLV-II is regarded as a risk marker for blood transfusion since it is mainly found in intravenous drug users world-wide (Vandamme et al., Evolutionary strategies of human T-cell lymphotropic virus type II, Gene 261 (2000) 171-180). Both viruses are spread globally, but the prevalence of HTLV-I is highest in hot spot regions in Southern Japan (Kyushu, Shikoku and Okinawa), Sub-Saharan Africa, the Caribbean (Jamaica and Haiti) and South America.
• the major transmission modes of HTLV-I/II are through sexual contact, blood transfusion, sharing injection needles and mother to child transmission through breast-feeding.
• the seroconversion period after HTLV infection is long when compared to other infectious diseases.
• the window period, i.e. the time frame after infection within which no antibodies against the virus can be detected may range from several weeks to months.
• immunoassays for detecting anti-HTLV-antibodies often use polypeptides derived from the envelope of the virus (gp46 surface protein and gp21 transmembrane protein) or from the gag-encoded p24 capsid protein.
• peptidic and recombinant variants of the p24 capsid protein have been used as antigens in immunoassays.
• antigens By means of these antigens, anti-p24 immunoglobulins of the G- type have been detected with high accuracy and satisfying sensitivity.
• p24 capsid antigens of this kind are, however, not able to bind and detect immunoglobulins of the M type. Since IgM molecules usually appear before IgG molecules during seroconversion, we reasoned that it should be worthwhile to modify recombinant p24 capsid antigen in a way that it is recognized and bound by IgM.
• the problem underlying the invention therefore is the development of an immunoassay for detecting antibodies against HTLV-I and HTLV-II that overcomes the limited seroconversion sensitivity of the hitherto available immunoassays.
• the invention concerns soluble HTLV p24 antigens that are fused to chaperones and their use in diagnostic applications such as immunoassays for detecting antibodies against HTLV-I or HTLV-II in an isolated biological sample.
• the invention relates to soluble HTLV-I or HTLV-II p24 antigen fragments comprising either the N- or the C-terminal domain of the p24 sequence wherein the HTLV p24 antigen fragment may be fused to a chaperone.
• the invention covers recombinant DNA molecules encoding these HTLV-I and -II fusion antigens as well as their recombinant production using expression vectors and host cells transformed with such expression vectors.
• the invention focusses on compositions of several of these HTLV p24 antigens and on an immunoassay method for detection of HTLV antibodies using the antigens of the invention. Also the use of HTLV p24 antigens in an in vitro diagnostic assay as well as a reagent kit for detection of anti-HTLV-antibodies comprising said HTLV p24 antigens is encompassed.
• SEP ID NO. 1 p24/HTLV-I (146-344)// P10274, 199 amino acid residues
• HTLV-I p24 sequence Shows the HTLV-I p24 sequence as retrieved from SwissProt database ID P10274 (146-344 Gag-Pro polyprotein from Human T-cell leukemia virus 1, strain Japan AT -1 subtype A). The numbering refers to the immature polyprotein precursor (sequence of aa 1-130 refers to matrix protein pi 9). Note that the N-terminal 15 amino acid residues from aa 131-145 (proline rich sequence) have been omitted.
• SEQ ID NO. 2 p24 NTD (146-260VHTLV-I, 115 amino acid residues
• HTLV-II p24 sequence Shows the HTLV-II p24 sequence as retrieved from SwissProt database ID P03353 (152-3350 Gag-Pro polyprotein from Human T-cell leukemia virus 2).
• the numbering refers to the immature polyprotein precursor (sequence of aa 1-136 refers to matrix protein pl9). Note that the N-terminal 15 amino acids from aa 137-151 (proline rich sequence) have been omitted.
• HTLV-II p24 sequence similar to SEQ ID NO. 5 with regard to length and position.
• Ec in the protein designations for i3 ⁇ 4SlyD, iicFkpA and ⁇ cSkp indicate the protein sequence origin from Escherichia coli.
• Each protein bears a hexa-histidine tag at its C-terminal end which is used to facilitate protein purification and refolding.
• SEQ ID NO. 17 gly cine-rich linker between fused polypeptides (see example 1) GGGSGGGSGG GSGGGSGGGS GGG
• PILRSLAYSN A KEAQKILQ ARGHTNSPLG EMLRTAQAWT PKDKTKVLLE HHHHHH
• TKVLLEHHHH HH SEP ID NO. 21 £cFkpA-p24/CTD(267-350yHTLV-II
• X C, A or S.
• SLASGKSLLH EVDKDISQLT QAIVKNHKNL LKIAQYAAQN RRGLDLLF E QGGLXKALQE QXXFLNITNS HVSILQERPP LENRVLTGWG LNWDLGLSQW AREALQTG HTLV gp21 may also be advantageously applied as a solubility-enhanced chaperone fusion polypeptide as shown for example in SEQ ID NOs. 26 and 27
• Fig. 1 shows the near UV CD spectrum of Skp-p24/CTD (267-350), SEQ ID NO. 22.
• Fig. 2 shows the melting curve of Skp-p24/CTD (SEQ ID NO. 22). Thermally induced unfolding and refolding is monitored by near UV CD spectroscopy at 277 nm.
• Fig. 3 shows the near UV CD spectrum of FkpA-p24/CTD (267-350), SEQ ID NO. 21.
• Fig. 4 shows that the near UV CD signal of the native FkpA-p24/CTD molecule is fully restored after a thermally induced unfolding/refolding cycle.
• HTLV p24 is a crucial antigen for the detection of anti-HTLV antibodies.
• the p24 capsid protein has been known in the art for a long time and has been used in immunoassays for detection of anti-HTLV antibodies (Manns et al., Blood (1991) 77: 896-905).
• Immunoassays for the detection of both IgG and IgM molecules require a set of antigens that are recognized and bound not only by IgG molecules but also by IgM molecules.
• IgM molecules typically occur in the early phase of seroconversion upon infection with HTLV.
• the binding of the polyvalent IgM molecules is critically dependent on a high antigen epitope density. Thus, it is imperative that antigens designed for the specific detection of IgM molecules possess and display such a high epitope density.
• a conventional way to generate IgM detection modules with high epitope density would be to polymerize monomeric antigens by means of chemical crosslinking.
• chemical crosslinking There is a wealth of homobifunctional and heterobifunctional crosslinkers that may be used with great advantage and that are well known in the art.
• homobifunctional and heterobifunctional crosslinkers that may be used with great advantage and that are well known in the art.
• IgM detection modules may interfere with the reversibility of protein folding/unfolding, and it may, additionally, be the source of interference problems which have to be overcome by anti-interference strategies in the immunoassay mixture.
• a more recent technique of generating IgM detection modules is to fuse the antigen of interest to an oligomeric chaperone, thereby conveying high epitope density to the antigen.
• the advantage of this technology lies in its high reproducibility and in the triple function of the oligomeric chaperone fusion partner: firstly, the chaperone enhances the expression rate of the fusion polypeptide in the host cell, secondly, the chaperone facilitates the refolding process of the target antigen and enhances its overall solubility and, thirdly, it assembles the target antigen reproducibly into an ordered oligomeric structure.
• European patent application publication no. EP1982993 A2 discloses a method and tools for early detection of true primary infections by pathogens such as human cytomegalovirus using antigens that are fused to oligomeric chaperones. However, this publication is silent with regard to detection of HTLV infection.
• a protein domain is an autonomously folding entity within a protein structure, that is, a protein domain is not dependent on other parts or regions of the protein in its folding.
• WW domain amino acid residues
• many natural protein domains have been elucidated, ranging in size from ⁇ 40 amino acid residues (WW domain) to more than 300 amino acid residues. It has also been demonstrated that very small, yet stable protein domains may be designed from the scratch: artificial polypeptide sequences with fragment lengths from 23-28 amino acid sequences have been shown to fold
• NTD N- terminal domain
• CCD C-terminal domain
• CTD exhibited excellent signal dynamics in that it generated high signals with positive sera and very low signals with negative sera. This is surprising, since the CTD is presumed to harbor a natural dimerization motif needed for p24 capsid assembly. By virtue of its natural oligomerization behavior, we had reasoned that the CTD would exhibit an aggregation tendency that is significantly higher than the aggregation tendency of the NTD.
• p24 CTD When fused to chaperones such as SlyD, FkpA or Skp, p24 CTD remains soluble, stable and is well-suited for the detection of IgM molecules which typically occur in the early phase of seroconversion upon infection with HTLV.
• the oligomeric FkpA and Skp fusion variants of p24 CTD may serve to enhance the sensitivity of HTLV-immunoassays.
• IMAC immobilized metal chelate chromatography
• the oligomeric species FkpA-p24/CTD and Skp-p24/CTD may be used advantageously as specifiers on both sides of a DAGS format (e.g. FkpA-p24/CTD-biotin and Skp-p24/CTD-ruthenium).
• a DAGS format e.g. FkpA-p24/CTD-biotin and Skp-p24/CTD-ruthenium.
• the invention therefore concerns soluble HTLV p24 antigens that comprise either the N- terminal domain and lack the C-terminal domain or that comprise the C-terminal domain of the full-length HTLV p24 polypeptide and lack the N-terminal domain, respectively.
• the p24 antigens can be fused to chaperones. Also encompassed is the use of these HTLV p24 antigens in diagnostic applications such as immunoassays for detecting antibodies against HTLV-I or HTLV-II in an isolated biological sample.
• HTLV means "human T-cell lymphotropic virus”. Unless specifically marked as HTLV-I or HTLV-II the term HTLV refers to both virus types.
• the antigen comprises only a certain domain of the complete HTLV p24 antigen such as the N-terminal domain (NTD) or the C-terminal domain (CTD).
• the antigen comprises the N-terminal domain of SEQ ID NO. 2 or the C-terminal domain of SEQ ID NO. 3 of HTLV-I p24.
• the fusion antigen preferably comprises the N-terminal domain of SEQ ID NO. 6 or the C-terminal domain of SEQ ID. NO. 7. In a further preferred mode, if the N-terminal domain is part of the antigen the C-terminal domain is missing and vice versa.
• the invention concerns a soluble HTLV p24 antigen comprising the N-terminal domain (NTD) of HTLV p24 as specified in SEQ ID NO. 2 (p24 NTD HTLV-I) or SEQ ID NO. 6 (p24 NTD HTLV-II) wherein said HTLV p24 antigen lacks the C-terminal domain (CTD) as specified in SEQ ID NO. 3 (p24 CTD HTLV-I) and in SEQ ID NO. 7 (p24 CTD HTLV-II).
• NTD N-terminal domain
• CTD C-terminal domain
• the invention concerns a soluble HTLV p24 antigen comprising the C-terminal domain of HTLV p24 as specified in SEQ ID NO. 3 (p24 CTD HTLV-I) or SEQ ID NO. 7 (p24 CDT HTLV-II) wherein said HTLV p24 antigen lacks the N-terminal domain as specified in SEQ ID NO. 2 (p24 NTD HTLV-I) and in SEQ ID NO. 6 (p24 NTD HTLV-II).
• HTLV p24 antigen encompasses also variants.
• HTLV p24 variants may easily be created by a person skilled in the art by conservative or homologous substitutions of the disclosed amino acid sequences (such as e.g. substitutions of a cysteine by alanine or serine).
• variants in this context also relates to a protein or a protein fragment (i.e. a polypeptide or peptide) substantially similar to said protein. For example, modifications such as C- or N-terminal truncations by 1 to 10 amino acids are within the scope of the claimed HTLV p24 antigens.
• a variant may be an isoform which shows amino acid exchanges, deletions or insertions compared to the amino acid sequence of the most prevalent protein isoform.
• a substantially similar protein has a sequence similarity to the most prevalent isoform of the protein of at least 80%, in another embodiment at least 85% or at least 90%, in yet another embodiment at least 95%.
• the term "variant” also relates to a post-translationally modifed protein such as a glycosylated or phosphorylated protein.
• a variant classifies as a HTLV p24 antigen variant as long as the immunoreactivity in an in vitro diagnostic immunoassay is maintained, i. e.
• variant is also a protein or antigen which has been modified for example by covalent or non-covalent attachment of a label or carrier moiety to the protein or antigen.
• Possible labels are radioactive, fluorescent, chemiluminescent, electrochemiluminescent, enzymes or others e.g. like digoxigenin or biotin. These labels are known to a person skilled in the art.
• the HTLV p24 antigens of the current invention are soluble, stable and immunoreactive, i. e. they are suitable as antigens for use in an immunological assay.
• the antigens according to the invention are soluble under physiological buffer conditions, for example in a phosphate buffer system at ambient temperature without addition of detergents.
• the antigens are also capable of binding to or being recognized and bound by antibodies specific for HTLV p24, like e.g. anti- p24 antibodies present in an isolated sample such as human sera.
• the HTLV p24 antigens according to the invention may be fused to a chaperone.
• fusion protein refers to a protein comprising at least one protein part corresponding to a HTLV p24 polypeptide and at least one protein part derived from a chaperone that serves the role of a fusion partner.
• Chaperones which are known as classical folding helpers, are proteins that assist the folding and maintenance of the structural integrity of other proteins. Examples of folding helpers are described in detail in WO 03/000877. According to the invention chaperones of the peptidyl prolyl isomerase class such as chaperones of the FKBP family can be used for fusion to the HTLV p24 antigen variants. Examples of FKBP chaperones suitable as fusion partners are
• a further chaperone suitable as a fusion partner for HTLV p24 is Skp, a trimeric chaperone from the periplasm of E.coli, not belonging to the FKBP family. It is not always necessary to use the complete sequence of a chaperone. Functional fragments of chaperones (so-called binding-competent modules) which still possess the required abilities and functions may also be used (cf. WO 98/13496).
• At least one or at least two modules of an FKBP chaperone such as e.g. E. coli SlyD, SlpA or FkpA are used as fusion moieties for expression of the HTLV p24 antigens.
• the chaperone Skp may be used as a fusion partner as well.
• the fusion of two FKBP-chaperone domains results in improved solubility of the resulting fusion polypeptide.
• the fusion moieties may be located at the N-terminus or at the C-terminus or at both ends (sandwich-like) of the HTLV p24 antigen.
• the HTLV p24 antigens according to the invention are fused to an oligomeric chaperone.
• Oligomeric chaperones are chaperones that naturally form dimers, trimers or even higher multimers so that a plurality of monomeric subunits are assembled by specific non- covalent interactions.
• Preferred oligomeric chaperones are FkpA and Skp.
• Particularly preferred is a soluble HTLV p24 antigen fused to a chaperone selected from the group consisting of SEQ ID NOs. 9 to 16 and 18 to 24.
• the HTLV p24 antigens according to the invention can be generated and prepared by means of recombinant DNA techniques. Another aspect of the invention therefore is a recombinant DNA molecule encoding a HTLV p24 antigen and variants thereof as defined further above.
• recombinant DNA molecule refers to a molecule which is made by the combination of two otherwise separated segments of DNA sequence accomplished by the artificial manipulation of isolated segments of polynucleotides by genetic engineering techniques or by chemical synthesis. In doing so one may join together polynucleotide segments of desired functions to generate a desired combination of functions.
• Recombinant DNA techniques for expression of proteins in prokaryotic or lower or higher eukaryotic host cells are well known in the art. They have been described e.g. by Sambrook et al., (1989, Molecular Cloning: A Laboratory Manual)
• the recombinant DNA molecules according to the invention may also contain sequences encoding linker peptides of 10 to 100 amino acid residues in between the HTLV p24 antigen and the fusion moieties and also between several fusion moieties.
• linker sequence may for example harbor a proteolytic cleavage site.
• a further aspect of the invention is an expression vector comprising operably linked a recombinant DNA molecule according to the present invention, i.e., a recombinant DNA molecule encoding an HTLV p24 antigen and optionally a peptidyl prolyl isomerase chaperone, such as an FKBP-chaperone, wherein the FKBP-chaperone is selected from FkpA, SlyD and SlpA.
• the recombinant DNA molecule encodes a fusion protein comprising an HTLV p24 antigen and Skp.
• the expression vector comprising a recombinant DNA according to the present invention may be used to express the HTLV p24 antigen in a cell free translation system or may be used to transform a host cell for expression of the HTLV p24 antigen according to methods well known in the art. Another aspect of the invention therefore relates to a host cell transformed with an expression vector according to the present invention.
• the recombinant HTLV p24 antigens are produced in E. coli cells.
• An additional aspect is a method for producing a soluble, stable and immunoreactive HTLV p24 antigen according to the invention.
• Said p24 antigen may be produced as a fusion protein containing the HTLV p24 antigen and a chaperone.
• a chaperone such as Skp or a peptidyl prolyl isomerase class chaperone like an FKBP chaperone is used.
• said FKBP chaperone is selected from the group consisting of SlyD, FkpA and SlpA.
• This method comprises the steps of
• HTLV p24 antigen is brought into a soluble and immunoreactive conformation by means of refolding techniques known in the art.
• An additional aspect of the present invention concerns a method for the detection of anti- HTLV antibodies in an isolated human sample wherein an HTLV p24 antigen according to the invention is used as a binding partner for the antibodies.
• the invention thus covers a method for the detection of antibodies specific for HTLV in an isolated sample, said method comprising
• said method is suitable for detecting HTLV antibodies of the IgG and the IgM subclass.
• Immunoassays for detection of antibodies are well known in the art, and so are methods for carrying out such assays and practical applications and procedures.
• the HTLV p24 antigens according to the invention can be used to improve assays for the detection of anti-HTLV antibodies independently of the labels used and independently of the mode of detection (e.g., radioisotope assay, enzyme immunoassay, electrochemilummescence assay, etc.) or the assay principle (e.g., test strip assay, sandwich assay, indirect test concept or homogenous assay, etc.). All biological liquids known to the expert can be used as isolated samples for the detection of anti-HTLV antibodies.
• the samples usually used are bodily liquids like whole blood, blood sera, blood plasma, urine or saliva.
• a further embodiment of the invention is an immunoassay for detecting anti-HTLV antibodies in an isolated sample performed according to the so-called double antigen sandwich concept (DAGS).
• DGS double antigen sandwich concept
• this assay concept is also termed double antigen bridge concept, because the two antigens are bridged by an antibody analyte.
• the ability of an antibody to bind at least two different molecules of a given antigen with its two (IgG, IgE), four (IgA) or ten (IgM) paratopes is required and utilized.
• an immunoassay for the determination of anti-HTLV antibodies according to the double antigen bridge format is carried out by incubating a sample containing the anti- HTLV antibodies with two different HTLV p24 antigens, i.e. a first ("solid phase") HTLV p24 antigen and a second HTLV p24 ("detection") antigen, wherein each of the said antigens binds specifically to said anti-HTLV antibodies.
• the first antigen can be bound directly or indirectly to a solid phase and usually carries an effector group which is part of a bioaffme binding pair like, e.g., biotin and avidin.
• the solid phase is coated with either avidin or streptavidin.
• the second antigen carries a label.
• an immunoreaction admixture is formed comprising the first antigen, the sample antibody and the second antigen.
• a solid phase to which the first antigen can be bound is added either before the addition of the sample to said antigens or after the immunoreaction admixture is formed.
• This immunoreaction admixture is maintained for a time period sufficient for allowing anti-HTLV antibodies against said HTLV p24 antigens in the body fluid sample to immunoreact with said HTLV p24 antigens to form an immunoreaction product.
• Next step is a separation step wherein the liquid phase is separated from the solid phase. Finally, the presence of any of said immunoreaction product is detected in the solid or liquid phase or both.
• DAGS immunoassay the basic structures of the "solid phase antigen” and the “detection antigen” are essentially the same. It is also possible to use, in a double antigen bridge assay, similar but different HTLV p24 antigens, which are immunologically cross- reactive. The essential requirement for performing such assays is that the relevant epitope or the relevant epitopes are present on both antigens. According to the invention it is possible to use different fusion moieties for each HTLV p24 antigen (e.g. SlyD fused to HTLV p24 on the solid phase side and FkpA p24 fused to HTLV p24 on the detection side) as such variations significantly alleviate the problem of non-specific binding and thus mitigate the risk of false-positive results.
• SlyD fused to HTLV p24 on the solid phase side and FkpA p24 fused to HTLV p24 on the detection side as such variations significantly alleviate the problem of non-specific binding and thus mitigate the
• an asymmetric format is applied, combining an HTLV p24 fused to FkpA and an HTLV p24 antigen fused to Skp. More preferably, the
• the HTLV p24 fused to FkpA is used on the solid phase side and the HTLV p24 fused to Skp is applied on the detection side but it is also possible to have a reversed arrangement, i.e. an HTLV p24 antigen fused to Skp on the solid phase side and the HTLV p24 fused to FkpA on the detection side.
• the HTLV p24 FkpA fusion protein carries a biotin moiety for attachment to a solid phase that has been coated with streptavidin or avidin and the HTLV p24 Skp fusion protein carries an electrochemiluminescent label such as ruthenium complexes.
• a further embodiment of the present invention is therefore an immunoassay according to the double antigen bridge concept wherein a first HTLV p24 antigen according to the present invention, and a second HTLV p24 antigen according to the present invention are used.
• the present invention further relates to the use of at least one antigen of HTLV p24 in a diagnostic test for the detection of anti-HTLV antibodies.
• An additional subject matter of the invention is a reagent kit for the detection of antibodies against HTLV, containing, in addition to the usual test additives for immunoassays, at least one antigen of the HTLV p24 antigens according to the invention suitable for specifically binding to HTLV antibodies to be determined and possibly carrying a label as well as other usual additives if necessary.
• the reagent kit contains an HTLV p24 antigen according to any of SEQ ID NOs. 9 tol6 and l8 to 24.
• the reagent kits defined above contain controls and standard solutions as well as reagents in one or more solutions with the common additives, buffers, salts, detergents etc. as used by the average man skilled in the art along with instructions for use.
• compositions comprising a soluble HTLV p24 antigen according to the current invention and an HTLV env antigen, preferably gp21 comprising SEQ ID NO. 25.
• composition refers to separately expressed polypeptides that are present as individual distinct molecules in a mixture.
• composition excludes a protein that bears p24 and gp21 fragments on a single polypeptide chain.
• compositions comprising the C-terminal domains of HTLV p24, particularly preferred is a composition comprising an HTLV-I p24 antigen according to SEQ ID NO. 3 (lacking SEQ ID NO. 2) and/or an HTLV-II p24 antigen according to SEQ ID NO. 7 (lacking SEQ ID NO. 6) and HTLV gp21.
• an HTLV gp21 sequence comprising any of SEQ ID NOs. 25, 26 or 27 can be present.
• the composition comprises each HTLV antigen in two forms, i.e. in a form that enables the antigen to be attached to a solid phase (e.g. a biotinylated antigen that can bind to a surface coated with streptavidin) and in a labeled form that enables detection of the immunocomplex between HTLV antibodies present in the sample and the applied HTLV antigens.
• the invention also concerns the use of a HTLV p24 antigen according to the invention in an in vitro diagnostic test for the detection of anti-HTLV antibodies.
• Example 1 The invention is further illustrated by the Examples.
• Example 1 The invention is further illustrated by the Examples.
• Example 1 The invention is further illustrated by the Examples.
• a synthetic gene encoding p24 capsid antigen aa 146-344 (numbering refers to the Gag-Pro polyprotein precursor) from HTLV-I (lacking the pro line-rich 15 amino acids at the N-terminus of the mature capsid protein) with a glycine-rich linker region fused in frame to the N-terminus was purchased from
• Ndel and BamHI restriction sites were at the 5 ' and 3' ends of this cassette, respectively.
• the genes and the restriction sites were designed to enable the in frame fusion of the chaperone part iicSlyD-iicSlyD and the p24 antigen part by simple ligation.
• the nucleotide sequences encoding the Ec lyO units were degenerated as were the nucleotide sequences encoding the extended linker regions, i.e., different codon combinations were used to encode identical amino acid sequences.
• the pET24a vector was digested with Ndel and Xhol and the cassette comprising tandem-
• the drawing below shows a scheme of the N-terminally truncated HTLV-I p24 antigen 146- 344 bearing two SlyD chaperone units fused in frame to its N-terminal end.
• the depicted fusion polypeptide has been named £cSlyD-£cSlyD-p24 (146-344).
• E. coli BL21 (DE3) cells harboring the particular pET24a expression plasmid were grown at 37°C in LB medium plus kanamycin (30 ⁇ g/ml) to an OD 6 oo of 1.5, and cytosolic overexpression was induced by adding 1 mM isopropyl-B-D-thiogalactoside. Three hours after induction, cells were harvested by centrifugation (20 min at 5000 g), frozen and stored at -20°C.
• the frozen pellet was resuspended in chilled 50 mM sodium phosphate pH 8.0, 7.0 M GdmCl, 5 mM imidazole and the suspension was stirred for 2 h on ice to complete cell lysis.
• the crude lysate was applied onto a Ni- NT A column equilibrated with the lysis buffer including 5.0 mM TCEP.
• the subsequent washing step was tailored for the respective target protein and ranged from 5 to 15 mM imidazole (in 50 mM sodium phosphate pH 8.0, 7.0 M GdmCl, 5.0 mM TCEP). At least 10- 1 volumes of the washing buffer were applied.
• the GdmCl solution was replaced by 50 mM potassium phosphate pH 8.0, 100 mM KCl, 10 mM imidazole, 5.0 mM TCEP to induce conformational refolding of the matrix-bound protein.
• a protease inhibitor cocktail (Complete ® EDTA-free, Roche) was included in the refolding buffer. A total of 15-20 column volumes of refolding buffer were applied in an overnight reaction. Then, both TCEP and the Complete ® EDTA-free inhibitor cocktail were removed by washing with 3-5 column volumes 50 mM potassium phosphate pH 8.0, 100 mM KCl, 10 mM imidazole.
• the native protein was then eluted by 500 mM imidazole in the same buffer. Protein-containing fractions were assessed for purity by Tricine-SDS-PAGE and pooled. Finally, the proteins were subjected to size-exclusion-chromatography (Superdex HiLoad, Amersham Pharmacia) and the protein-containing fractions were pooled and concentrated to 10-20 mg/ml in an Amicon cell (YM10). After the coupled purification and refolding protocol, protein yields of roughly 10-30 mg could be obtained from 1 g of E. coli wet cells, depending on the respective target protein.
• Protein concentration measurements were performed with an Uvikon XL double-beam spectrophotometer.
• the molar extinction coefficients (s 28 o) were determined by using the procedure described by Pace (1995), Protein Sci. 4, 2411-2423.
• the molar extinction coefficients ( ⁇ M28O) used for the distinct fusion polypeptides are specified in table 1.
• Table 1 Protein parameters of the p24 fusion polypeptide variants generated and used in this study. All parameters are referring to the respective protein monomers.
• the lysine ⁇ -amino groups of the fusion polypeptides were modified at protein concentrations of 10-30 mg/ml with N-hydroxy-succinimide activated biotin and ruthenium label molecules, respectively.
• the label/protein ratio varied from 2: 1 to 5:1 (mohmol), depending on the respective fusion protein.
• the reaction buffer was 150 mM potassium phosphate pH 8.0, 100 mM KC1, 0.5 mM EDTA.
• the reaction was carried out at room temperature for 15 min and stopped by adding buffered L-lysine to a final concentration of 10 mM.
• the respective stock solutions were prepared in dried DMSO
• the immunological reactivity (antigenicity) of the polypeptide fusion variants of HTLV p24 capsid antigen was assessed in automated Elecsys ® 2010 and cobas e 411 analyzers (Roche Diagnostics GmbH). Elecsys ® is a registered trademark of the Roche group. Measurements were carried out in the double antigen sandwich format.
• Signal detection in Elecsys ® 2010 and cobas e 411 is based on electrochemiluminescence.
• the biotin-conjugate i.e. the capture-antigen
• the detection-antigen bears a complexed Ruthenium cation (switching between the redox states 2+ and 3+) as the signaling moiety.
• the chromogenic ruthenium complex is bridged to the solid phase and emits light at 620 nm after excitation at a platinum electrode.
• the signal output is in relative light units.
• recombinant p24 capsid antigen fusion polypeptides were assessed in a double antigen sandwich (DAGS) immunoassay format.
• recombinant HTLV-I capsid antigen p24 was used as a biotin and a ruthenium conjugate, respectively, to detect anti-p24 antibodies in human sera.
• p24 is one of the immunodominant antigens of HTLV, and soluble variants of p24 - as disclosed in this patent application - are invaluable tools for the detection of HTLV infections.
• NTD N-terminal domain
• p24 the oligomeric form of p24 NTD is better suited to detect antibodies that appear in the early phase of seroconversion (i.e., immunoglobulins of the M-type), which is exemplified in particular with the seroconversion panels K5647 and K5648 (Table 2, columns 3 and 4).
• seroconversion panels K5647 and K5648 Table 2, columns 3 and 4.
• the background signals of the oligomeric NTD p24 are significantly increased when compared to CTD p24.
• the antigenicity of the C-terminal domain of p24 seems to outdistance the antigenicity of the N-terminal domain.
• the oligomeric C-terminal domain of p24 possesses outstanding physicochemical and superior antigenic properties making it an attractive candidate for HTLV serology. It is clearly superior to full-length p24 (146-344, numbering of Gag-pro polyprotein precursor) in terms of sensitivity in early IgM detection. Since the Skp fusion polypeptide of full length p24 (146-344) was not available as it significantly tended to aggregate, we were confined to SlyD-SlyD and FkpA fusion polypeptides of the p24 full-length version.
• epitopes in the N and C-domain of p24 are sufficient to warrant a sensitive and reliable detection of IgM molecules in the early phase of HTLV infection - provided that these epitopes are offered in an oligomeric form.
• the C-terminal domain of p24 from HTLV-I holds promise as an invaluable ingredient in a HTLV immunoassay. This was somewhat unexpected: since the C-domain of the p24 capsid antigen is presumably involved in p24 oligomerization (Khorasanizadeh et al., J. Mol. Biol.
• Table 2 superior irnmunoreactivity of oligomeric p24 variants in early HTLV infections (increased sensitivity in rabbit seroconversion panels).
• the immunoassay was essentially performed as described in Example 4.
• Oligomeric chaperones such as FkpA and Skp may be used advantageously as fusion partners in order to achieve a functional oligomerization of their respective client antigens. Fusion of FkpA or Skp to target proteins (i.e. , their client or guest antigens) may yield well-defined oligomeric fusion polypeptides which are suited for the detection of IgM molecules in immunoassays.
• target proteins i.e. , their client or guest antigens
• DAGS double antigen sandwich
• biotin and ruthenium conjugates of purified recombinant EcSkp and iicFkpA were prepared as described in example 3. That is, the purified chaperones (i.e., the naked chaperones without any fused target sequences) were biotinylated by means of an N- hydroxy-succinimide-activated biotin label. As well, ruthenylated chaperones (i.e., the naked chaperones without any fused target sequences) were produced by means of an N-hydroxy- succinimide-activated ruthenium label.
• Near-UV CD spectra were recorded with a Jasco-720 spectropolarimeter with a thermostatted cell holder and converted to mean residue ellipticity.
• the buffer was 150 mM potassium phosphate pH 8.0, 100 mM C1, 0.5 mM EDTA.
• the pathlength was 0.2 cm
• the protein concentration was 218 ⁇ (referring to Skp-p24 monomer) or 147.5 ⁇ (referring to FkpA- p24 monomer).
• the measuring range was 250 - 330 nm
• the band width was 1.0 nm
• the scanning speed was 20 nm/min at a resolution of 0.5 nm and the response was 1 s.
• spectra were measured nine times and averaged.
• Circular dichroism spectroscopy is the method of choice to assess both the secondary and the tertiary structure of proteins.
• Ellipticity in the aromatic region 250-330 nm
• tertiary contacts within a protein i.e., the globular structure of a regularly folded protein
• melting curves were monitored in the near UV region at detection wavelengths of 277 and 280 nm, respectively.
• the temperature range was 20-75 °C
• the band width was 2.0 nm
• the temperature slope was l°C/min
• the response was 2 s.
• the thermally-induced unfolding was monitored at 277 and 280 nm, corresponding to the maximal signal amplitudes for Skp-p24/CTD and FkpA-p24/CTD, respectively.
• this thermally induced unfolding (as monitored at 277 nm) is reflected in an increase in the CD signal as shown in Figure 2.
• Skp-p24/CTD obviously retains its native -like fold and its trimeric structure up to 55°C. The onset of unfolding is between 55°C and 60°C.
• Skp-p24/CTD is obviously able to readopt its native-like conformation when the protein solution is chilled to 20°C. Indeed, the near UV CD spectra monitored before and after the thermally induced unfolding virtually superimpose (see Figure 1). In conclusion, Skp-p24/CTD possesses robust folding properties which are outstanding for a molecule with this degree of complexity and which are highly desired for an antigen that is used in an immunoassay.
• FkpA-p24/CTD just like Skp-p24/CTD, FkpA-p24/CTD exhibits a marked CD signal in the near UV region (250-330 nm, signal maximum at 280 nm), pointing to a well-ordered conformation after the matrix-coupled refolding process (Figure 3).
• the CD signal of FkpA- p24/CTD strongly decreases when the molecule unfolds and loses its tertiary structure ( Figure 4).
• Skp-p24/CTD and FkpA-p24/CTD possess very robust folding properties which are outstanding for molecules with this degree of complexity and which are highly desirable for fusion polypeptides that serve as antigenic ingredients, i.e., specifiers in an immunoassay.

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