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Title:  Pancreatic islet cell antigens obtained by molecular cloning

United States Patent:  6,811,989

Issued:  November 2, 2004

Inventors:  Rabin; Daniel U. (Branford, CT)

Assignee:  Bayer Corporation (West Haven, CT)

Appl. No.:  468581

Filed:  June 5, 1995

Abstract

Pancreatic islet cell antigens (ICA) that bind with antibodies found in the sera of patients afflicted with insulin-dependent (Type I) diabetes mellitus (IDDM). ICA proteins are expressed by recombinant cloning vehicles comprising DNA inserts isolated from islet cells. Full sequence native ICA proteins, or protein or peptide fragments thereof, can be used in the diagnosis of IDDM and in detecting or blocking human immunoglobulin, T-cells, or B-cells involved in IDDM.

Description of the Invention

BACKGROUND OF THE INVENTION

This invention relates to pancreatic islet cell antigens that bind with antibodies found in the sera of patients afflicted with insulin-dependent (Type I) diabetes mellitus (IDDM). More particularly, the invention relates to proteins and peptides that bind with islet cell antibodies (ICA) and that are prepared by recombinant DNA (rDNA) or synthetic methods. The invention also concerns cloned DNA encoding such ICA proteins and peptides. The ICA proteins and peptides of the present invention are useful as immunoassay reagents in the presymptomatic diagnosis of IDDM.

The accumulating evidence of cellular and humoral abnormalities associated with IDDM has led to the hypothesis that the disease is an autoimmune disorder. Serum antibodies directed against the insulin-producing beta cells of the pancreatic islets have been detected by immunofluorescence, [G. F. Bottazzo, A. Florin-Christensen, and D. Doniach: Islet Cell Antibodies in Diabetes Mellitus With Autoimmune Polyendocrine Deficiencies, Lancet ii:1279-1283 (1974), and A. C. MacCuish, J. Jordan, C. J. Campbell, L. J. P. Duncan, and W. J. Irvine: Antibodies to Islet-cell in Insulin-dependent Diabetics With Coexistent Autoimmune Disease, Lancet ii:1529-1533 (1974)]. These autoantibodies are observed in 70-80% of newly diagnosed diabetics (NDD), but only in 0.1-1% of normal control subjects [C. H. Brogren and A. Lernmark: Islet Cell Antibodies in Diabetes. Clin. Endocrinol. Metab. 11:409-430 (1982)], and G. F. Bottazzo, R. Pujol-Borrell, and D. Doniach: Humoral and Cellular Immunity in Diabetes Mellitus. Clin. Immunol. Allergy 1:139-159 (1981)]. ICAs have come to be accepted as one predictive factor for IDDM. A review of current knowledge on ICA is provided by A. Lernmark, Diabetic Medicine 4:285-292 (1987).

The conventional ICA assay consists of exposing pancreas sections to sera, staining with a second antibody bearing either a fluorescent [G. F. Bottazzo et al., supra] or enzyme label [P. G. Colman, M. Tatkus, A. Rabizadeh, C. Cahill, and G. S. Eisenbarth: Assay for Islet Cell Antibodies with Rat Pancreas and Peroxidase Protein A. Diabetes Care 11:367-368 (1988)], and observing under a microscope. Another similar method involves a biotin-avidin sandwich and immunofluorescent detection [T. Kobayashi, T. Sugimoto, T. Itoh, K. Kosaka, T. Tanaka, S. Suwa, K. Sato and K. Tsuju: The Prevalence of Islet Cell Antibodies in Japanese Insulin-dependent and Non-insulin-dependent Diabetic Patients Studied by Indirect Immunofluorescence and by a New Method. Diabetes 35:335-340 (1986)]. These methods are time consuming, laborious, difficult to reproduce, and have limited sensitivity. The development of a more convenient immunoassay for ICA would permit widespread testing for epidemiology and correlation with IDDM, and ultimately prediction of the disease with a screening test.

A major limitation of current ICA tests is the limited knowledge and characterization of the islet cell antigens involved. The ICA's may be of low titer or affinity and approachable only with characterized antigens. ICA antigens that are detected by the immunofluorescence test are of special interest; these antigens may include:

(1) islet cell surface moieties [N. K. MacLaren, S. W. Hugng, and J. Fogh: Antibody to Cultured Human Insulinoma Cells in Insulin-dependent Diabetes. Lancet 1:997-1000 (1975), and A. Lernmark, Z. R. Freedman, C. Hofmann, A. H. Rubenstein, D. F. Steiner, R. L. Jackson, R. J. Winter and H. S. Traisman: Islet-cell-surface Antibodies in Juvenile Diabetes Mellitus. N. Engl. J. Med. 299:375-380 (1978)],

(2) insulin [J. P. Palmer, C. M. Asplin, P. Clemons, K. Lyen, O. Tetpati, P. K. Raghu and T. L. Paquette: Insulin Antibodies in Insulin-dependent Diabetics Before Insulin Treatment. Science 222:1337-1339 (1983), and S. Srikanta, A. T. Ricker, D. K. McCulloch, J. S. Soeldner, G. S. Eisenbarth and J. P. Palmer: Autoimmunity to Insulin, Beta Cell Dysfunction, and Development of Insulin-dependent Diabetes Mellitus. Diabetes 35:139-142 (1986)],

(3) a 64,000 dalton (64 kd) islet protein of unknown cellular localization [S. Baekkeskov, J. H. Nielsen, B. Marner, T. Bilde, J. Ludvigsson, and A. Lernmark: Autoantibodies in Newly Diagnosed Diabetic Children Immunoprecipitate Human Pancreatic Islet Cell Proteins. Nature 298:167-169 (1982). Recent evidence indicates that the 64 kd protein is glutamic acid decarboxylase (GAD). [S. Baekkeskov, J-H. Aanstoot, S. Christgau, A. Reetz, M. Solimena, M. Cascalho, F. Folli, H. Richter-Olesen and P. De-Camilli: Identification of the 64k autoantigen in insulin-dependent diabetes as the GABA-synthesizing enzyme glutamic acid decarboxylase. Nature 347:151-156 (1990)],

(4) cytoplasmic antigens [G. F. Bottazzo, A. Florin-Christensen, and D. Doniach: Islet Cell Antibodies in Diabetes Mellitus With Autoimmune Polyendocrine Deficiencies. Lancet 2:1279-1283 (1974), A. C. MacCuish, J. Jordan, C. J. Campbell, L. J. P. Duncan, and W. J. Irvine: Antibodies to Islet-Cell in Insulin-Dependent Diabetics With Coexistent Autoimmune Disease. Lancet 2:1529-1533 (1974), R. Lendrum, G. Walker, and D. R. Gambli: Islet-Cell Antibodies in Juvenile Diabetes Mellitus of Recent Onset. Lancet 1:880-883 (1975), and W. J. Irvine, C. J. McCallum, R. S. Gray, G. J. Campbell, L. J. P. Duncan, J. W. Farquhar, H. Vaughan, and P. J. Morris: Pancreatic Islet Cell Antibodies in Diabetes Mellitus Correlated With The Duration and Type of Diabetes, Co-existent Autoimmune Disease, and HLA-type. Diabetes 26:138-147 (1977)],

(5) glycoconjugates [R. C. Nayak, M. A. K. Omar, A. Rabizadeh, S. Srikanta, and G. S. Eisenbarth, "Cytoplasmic" Islet Cell Antibodies: Evidence That the Target Antigen is a Sialoglycoconjugate. Diabetes 34:617-619 (1985); P. Vardi, E. E. Dibella, T. J. Pasquarello, and S. Srikanta, Islet Cell Autoantibodies: Pathobiology and Clinical Applications. Diabetes Care 10:645-56 (1987); B. K. Gillard, J. W. Thomas, L. J. Nell and D. M. Marcus, Antibodies Against Ganglioside GT3 in the Sera of Patients with Type I Diabetes Mellitus. Journal of Immunology 142:3826-32 (1989)].

Several reports indicate a high prevalence of anti-64 kd antibody in prediabetic sera as well as newly diagnosed diabetic sera [S. Baekkeskov, M. Landin, J. K. Kristensen, S. Srikanta, G. Jan Bruining, R. Mandrup-Poulsen, C. de Beaufort, J. S. Soeldner, G. Eisenbarth, F. Lindgren, G. Sundquist, and A. Lernmark: Antibodies to a 64,000 MW Human Islet Cell Antigen Precede the Clinical Onset of Insulin-dependent Diabetes. J. Clin. Invest. 79:926-934 (1987), M. A. Atkinson, N. K. Maclaren, W. J. Riley, D. W. Sharp and L. Holmes: Mr 64,000 Autoantibodies (64KA) Predict Insulin Dependent Diabetes. American Diabetes Assoc. 48th Annual Meeting (1988) Abstract #391, and M. A. Atkinson, N. K. Maclaren, D. W. Scharp, P. E. Lacy, and W. J. Riley: 64000 Mr autoantibodies as predictors of insulin-dependent diabetes. The Lancet 335:1357-1360 (1990)].

Some other molecular species have been characterized by Western blotting as being "common antigens" recognized by diabetic sera [D. G. Karounos, V. J. Virta, L. J. Nell, and J. W. Thomas: Analysis of Human and RINm5F Islet Cell Antigens. American Diabetes Assoc. Res. Symp. Woods Hole, Mass. October 1987; Abstract #120]. These antigens have molecular weights of 150 kd, 84 kd, 60 kd, 49 kd, and 36 kd. A more recent report from the same laboratory indicates that there is a RIN antigen of Mr 52,000 that reacts with 29% of diabetic sera. [D. G. Karounos and J. W. Thomas: Recognition of Common Islet Antigen by autoantibodies From NOD Mice and Humans With IDDM. Diabetes 39:1085-1090 (1990), D. G. Karounos, L. J. Nell, and J. W. Thomas: Autoantibodies present at onset of type I diabetes recognize multiple islet cell antigens. Autoimmunity 6:79-91(1990), and D. G. Karounos, J. S. is wolinsky, B. K. Gillard, and J. W. Thomas: Molecular Mimicry in Type I Diabetes: An Antigenic Determinant on a Rubella Virus Protein is Shared with a 52 kD Beta Cell autoantigen. Diabetes 39:96A (1990)]. The first and third references indicate that the 52,000 antigen is RIN specific, not found in human islets or other tissue.

SUMMARY OF THE INVENTION

The present invention provides a series of cloned nucleic acids that code for one or more proteins or protein fragments which bind selectively with pancreatic islet cell antibodies (ICA). Such cloned nucleic acids are characterized by the cDNA inserts in deposited recombinant bacteriophages ATCC 40550, 40551, 40552, 40553, 40554, 40703, 40704, 40705, 40706, and ICA-512.3.

The present invention, accordingly, also provides ICA proteins and peptide fragments thereof which are encoded by the cloned nucleic acids and are useful in the diagnosis of insulin-dependent (Type I) diabetes mellitus (IDDM). The ability of such proteins and peptides to bind to the antibody combining site on ICAs also confers utility in the binding or blocking of human immunoglobulin, T-cells or B-cells involved in IDDM, including circulating immunoglobulin, T-cells, and B-cells.

The ICA proteins and peptides of the present invention are obtained by such methods as full or partial expression, optionally with subsequent fragmentation, of the present cloned nucleic acids; and peptide or polypeptide synthesis based on the amino acid sequences determined from the present cloned cDNAs or from the full length ICA antigen genes that can be determined or isolated from islet cell nucleic acid libraries with the aid of the present complementary cloned cDNA sequences. Accordingly, such ICA proteins and peptides include the full length ICA proteins present in or on islet cells and which are expressed by the human gene whose mRNA is at least in part complementary with the complete sequence of the present cloned cDNAs. Also included in the ICA proteins and peptides of the present invention are the proteins expressed by recombinant cloning vehicles comprising the present cDNA inserts and fragments of such proteins obtained by partial expression or by subsequent fragmentation such as with restriction nucleases. The ICA proteins and peptides of the present invention also include peptides obtained by protein synthesis, such as those that are 3 amino acids in length or longer, which represent ICA epitopes or analogues or derivatives thereof.

The present invention offers a number of significant advantages. The molecular cloning of ICA antigens affords the preparation of large and reproducible amounts of material for use in research, diagnosis, and treatment of IDDM, as well as the opportunity to study the biological mechanisms involved in islet cell destruction and the appearance of ICA. The availability of large quantities of pure antigen enables the development of highly sensitive and specific immunoassays which can be used to screen the general population for presymptomatic IDDM or a predisposition to develop IDDM.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term "ICA antigens" shall be understood to refer to the proteins and peptides provided by the present invention even though it is recognized that in some cases peptide forms will not be "antigens" in the strict sense, i.e., they will be haptenic since they will require attachment to a conventional macromolecular carrier in order to stimulate the production of antibodies in a host animal.

Furthermore, the "cloned nucleic acids", "cloned ICA antigen sequences", "cDNA inserts", and like terms shall refer to the inserts in deposited recombinant phages ATCC 40550, 40551, 40552, 40553, 40554, 40703, 40704, 40705, 40706, and ICA-512.3, and also to other nucleic acid sequences of full length genes, or fragments of such sequences, comprising such deposited sequences. It will be recognized that one or more full length ICA antigens are characterized by homology with the above deposited cDNA inserts, however, it is possible that two or more of such cDNA inserts correspond to a single ICA antigen. For example, the insert in ATCC 40703 appears to encompass the inserts for both ATCC 40550 and ATCC 40554, and thus these three inserts may all correspond to different and/or overlapping portions of a single ICA antigen. Moreover, ATCC 40706 is comprised in ICA-512.3.

Preparation of Cloned ICA Antigen Sequences

In general, the cloned ICA antigen sequences is of the present invention are obtained by expressing human genes in a suitable recombinant cloning vehicle, e.g., bacteriophage, and probing the resulting gene library with IDDM serum to select antigens that are recognized by ICA antibodies. Recombinant antigens are then screened with a panel of diabetic and normal sera to determine the disease specificity of the identified clones.

The particular deposited clones were more particularly obtained by the following method (further details can be found in the Examples below). A human cDNA library was generated by extracting RNA from purified human islets. This RNA was fractionated by chromatography to separate poly-A mRNA from other RNA such as ribosomal RNA and fragments of degraded RNA. The separated mRNA was reverse transcribed with a commercially available cDNA kit (Bethesda Research Laboratories), ligated to Eco RI DNA linkers, and ligated into lambda gt-11 arms for in vitro packaging. The ligated lambda was packaged using a commercial kit (Stratagene) and then amplified on a bacterial lawn in a plate format.

The phage library was screened with antibodies from autoimmune patients with Type I diabetes. Agarose plates were spread with bacteria infected with the phage, and recombinant protein expression was induced chemically. The protein was deposited onto filters which were then probed with serum. Plaques that appeared to be positive were isolated from the agarose plates and purified through two rounds of isolation. Subsequent to cloning, the gt-11 phage was infected into a bacterial host for large scale expression. Specificity of the proteins expressed by the cloned cDNA was evaluated by Western blotting of bacterial extracts containing the cloned human protein. Preparative polyacrylamide gels were run and electroblotted onto membranes, the membranes were cut into strips, and then reacted with a series of normal and diabetic sera. The clones that generated proteins that reacted exclusively or predominantly with diabetic sera were selected.

Recombinant Cloning Vehicles and Subcloning

As is conventionally known in the art, the cDNA transcripts of the present invention, such as library cDNA or cDNA inserts excised from a cloning vehicle, can be incorporated into a variety of recombinant cloning vehicles for amplification of sequences of interest and for expression of ICA antigens of interest. A recombinant cloning vehicle will be understood to be a biochemical molecule or structure, e.g., DNA, that allows insertion of polynucleotide sequences and replication of the inserted polynucleotide sequences when the vehicle is appropriately incorporated into a host cell. An expression vehicle additionally includes the property of expressing the protein encoded by the inserted polynucleotide. In an expression vector, the inserted ICA antigen sequence is operably linked to a suitable control sequence capable of effecting the expression of ICA antigen in a suitable host. The control sequence involved will vary according to the host and transformation method selected. These matters are within the ordinary skill of the art.

Suitable recombinant cloning vehicles include plasmids, viruses and bacteriophage, and integratable fragments of DNA (i.e., fragments integratable into the host genome by recombination). Expression vehicles are particularly preferred and are exemplified, without limitation, by bacterial pEMBL, pMMB, pUK, pATH, and pGEX, yeast pAAH5, pYE4, and pAB112, mammalian pRSV, vaccinia derived vectors, baculovirus derived vectors, papilloma derived vectors, retroviral vectors, and shuttle vectors such as pCDM8. For a review, see D. M. Glover, DNA Cloning: A Practical Approach (1985) IRL Press Ltd. Suitable host cells include procaryotes, yeast, and higher eucaryotic cells including mammalian cells.

Subcloning of cDNA inserts can involve excising the insert for ligation into a different cloning vehicle. The insert can be excised using the restriction enzyme corresponding to the linkers used in the original insertion or using restriction enzymes selected from a restriction map of the insert. The excised cDNA can be inserted into another suitable vector for sequencing, amplification, or expression as desired. Should the terminal restriction sites in the original cloning vehicle have been destroyed, other enzymes can be used to recover the insert and resulting flanking regions from the cloning vehicle deleted by conventional means.

Another method of preparing DNA fragments for insertion into a cloning vehicle is the use of polymerase chain reaction (PCR) amplification. This procedure can be used on ligation reaction products to amplify the amount of DNA and introduce desired restriction sites for subcloning. PCR can also be used to replicate a fragment with desired restriction sites for transfer from one vehicle into another vehicle.

Full-Length Gene Cloning

Fragments of the cDNA inserts of the present invention can be used to isolate full-length cDNA or genomic DNA clones from appropriate libraries by standard methods. The target library is spread on plates, allowed to grow, transferred to filters, and reacted with DNA probes. Such DNA probes are generated from restriction fragments of the cDNA inserts by such methods as end labeling, nick translation, random primed transcription, or photochemical means. Oligonucleotides can be synthesized, labeled, and used as hybridization probes. RNA probes can also be generated from subcloned cDNA by transcription from appropriate templates.

Recombinant cloning vehicles, e.g., phage or plasmids, that appear to react with the partial cDNA clones are re-screened and then restriction mapped. Promising clones are then sequenced to confirm the hybridization of the original probes and to obtain extended sequence information on the larger fragment. If full-length clones are not obtained in this procedure, the complete sequence of the nucleic acid coding for the human gene can be pieced together from overlapping sequences of cloned fragments.

An alternative method for obtaining longer fragments, and possibly full-length clones, uses antibodies raised against ICA antigens expressed by partial clones. After identifying an antigen of interest, it can be used as an immunogen to raise monoclonal or polyclonal antibodies of high titer and affinity. Such antibodies will enable the detection of longer cDNA clones and cDNA clones present in lower amounts in the library.

Antigen and Peptide Synthesis

ICA antigens, as defined herein, can be prepared in a number of different ways from the clones and sequence information provided by the present invention. One can simply express the proteins from ICA antigen clones obtained according to the present invention, particularly from the deposited clones. Such expressed proteins, or fragments or digestion products thereof, can be used as antigens for binding to islet cell antibodies. However, direct use of bacterial expression extracts may not be possible in some cases since human sera normally react nonspecifically with E. coli proteins. In such cases, the expressed ICA antigens can be isolated by conventional techniques such as electrophoretic separation followed by immobilization on membranes (Western blotting), or by column chromatography or affinity purification (e.g., anti-beta-galactosidase affinity resin chromatography or other conventional biochemical means, e.g., salt or temperature precipitation).

Alternatively, peptide fragments can be synthesized by well-known methods from the amino acid sequences deduced from experimentally determined DNA sequences of ICA antigen clones. Overlapping peptides can be synthesized and tested for reactivity with ICA sera. As reactive peptides are found, smaller peptides can be prepared in order to map the smallest reacting unit, i.e., the epitope.

Methods

A principal use of the ICA antigens provided by the present invention is in the diagnosis and prediction of IDDM. In such a method, a blood sample, normally a serum sample, is reacted with a selected one or series of ICA antigens and immunoreactivity determined by any conventional technique. It is further contemplated that the immunoreactivity profile with different ICA antigens can provide diagnostically significant information concerning the nature of the disease, e.g., subtypes, the state of the disease, the proximity to onset of the disease, the efficacy of therapy, e.g., immune therapy, and the like.

A further use of the present ICA antigens is in the identification, marking, or specific destruction of autoreactive B-cells. If autoantibodies have a deleterious effect in IDDM, it is contemplated that anti-B-cell therapy can slow or stem the progress of the disease from prediabetes to clinical IDDM.

Another use of the present ICA antigens is in the identification of islet-reactive T-cell populations. ICA antigens can serve as stimulating antigens for T-cell culture, permitting significantly improved T-cell cloning, identification, and growth. It is contemplated that ICA T-cell detection can be significant in the diagnosis of the pre-diabetic state, and that monitoring the level of autoreactive T-cells can give an indication of the progress of the disease and the utility of immune modulating therapies. Further, the generation of ICA T-cell cultures can provide an in vitro model for designing diabetic therapies. Finally, it is contemplated that T-cell immunization can halt or retard autoimmunity by generating a humoral response against self-destructive elements.

The ability of ICA antigens to bind to human ICA immunoglobulin and T-cells can be used to block the binding of ICA to islet cells and islet cell components in vivo, and therefore are contemplated to provide a direct therapeutic effect.

Claim 1 of 42 Claims

What is claimed is:

1. A method of diagnosing insulin dependent diabetes mellitus in a patient, comprising the steps of contacting a blood sample obtained from such patient with a polypeptide reagent comprising the amino acid sequence encoded by the DNA insert of a recombinant cloning vehicle selected from the group consisting of ATCC 40550, 40551, 40552, 40553, 40554, 40703, 40704, 40705, 40706, and 75030, or a fragment of such sequence, said fragment being capable of binding an islet cell autoantibody, and determining binding of antibody from the patient's blood sample to the polypeptide reagent, wherein the presence of said binding indicates a positive result.




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