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Background of the Invention

The present invention relates to isolated polynucleotid molecules useful for analyzing alloantigen phenotypes, t peptides encoded by these molecules, and to the diagnostic an therapeutic uses thereof relating to a human platelet Ba polymorphism, including a method for typing platelet membran glycoproteins which entails an analysis of amplified cDN produced from platelet mRNA or of genomic JNA.
Blood obtained from different individuals has been foun to have different antigenic and immune properties, to the exten that antibodies in the blood of one person may react wit antigens on red blood cells or platelets in the blood of anothe individual. These antigens are often found on membran glycoproteins present on the surface of the cells. Thes membrane glycoprotein antigens can induce the production o antibodies against them when they are introduced as foreig proteins in transfused blood or in fetal blood. Human platelet and red blood cells contain dozens of identifiable membran glycoprotein constituents, only some of which have been wel characterized.
Membrane glycoproteins which induce antibody productio in the same species are called "alloantigens." Alloantigens hav been characterized for both red blood cells and platelets. Recognized classes of red blood cell and platelet alloantigen have been described, over the past 30 years, based o observations of antibody reactions occurring when patients hav been exposed to blood from other individuals. The lack of sequenceable antigen protein and clonable antigen-encoding mRNA has prevented molecular characterization of the different alleles coding for many clinically important alloantigens.
One system of alloantigens, consisting of the platelet

Baka and Bakb alloantigens, are carried by the human platelet membrane glycoprotein Ilb-IIIa (GPIIb-GPIIIa) complex, which mediates platelet aggregation by providing functional receptors for fibrinogen on platelet surfaces. See Phillips, et al., Blood 71: 831-43 (1988) . GPIIb and GPIIIa are known to bear a number of clinically important, alloantigenic determinants which are responsible for eliciting an immune response in two well-described clinical syndromes, post-transfusion purpura (PTP) and neonatal alloimmune thrombocytopenia (NATP) . See Kunicki & Newman in CURRENT STUDIES IN HEMATOLOGY AND BLOOD TRANSFUSIO 18-32 (1986) ; Aster in ADVANCES IN IMMUNOLOGY AND BONE MARRO TRANSPLANTATION 103-118 (1984) .
The Bak alloantigen system is the second or third mos frequently implicated stimulus in these disorders. There are tw serologically defined, but molecularly undefined, allelic form of the Bak alloantigen, designated "Bak3" and MBak," which ar thought to be expression products of the GPIIb gene. von de Borne, et al., Vox Sang. 39:113 (1980); Kickler, et al., Blood: 71(4) :894 (1988); Keifel, et al., Vox Sang. 56:93 (1989). Th gene frequencies for these two alleles have been calculated to b 61% for Baka and 39% for Bakb, while the observed phenotypi frequencies are 37% for Baka homozygous, 15% for Bakb ho ozygous and 48% for heterozygous individuals, see Kickler, et al., Vo Sang. 56:93 (1989). Based upon these frequencies, th probability of fetal-maternal Bak incompatibility would b significant, but fewer than 5% of the cases of NATP (or 1/40,000 are attributable to Bak. This suggests that other factor contribute to the likelihood of developing NATP.
Determination of the amino acid sequence variations tha are presumably responsible for forming the relevant epitopes o red blood cell and platelet alloantigens has been achieved i only a few instances, due largely to the formidable difficultie in obtaining protein-sequence information from those often larg glycoproteins. In particular, the amino acid-sequence variati responsible for the relevant epitopes has not yet been report for either the Baka or Bakb forms of the 125 kilodalton (kd) GPI molecule.

Summary of the Invention

It is therefore an object of the present invention provide polynucleotide molecules that can be used in analyzi

Bak alloantigen.
It is also an object of the present invention to provi for the typing of human platelets, based on information obtain through the analysis of nucleic acids, including genomic DNA a cDNA derived from platelets, respectively.
It is yet another object of the present invention provide ready means for determining platelet Bak alloantig phenotype.
It is still a further object of the present invention provide polypeptide molecules for use in generating antibodi that distinguish between the different forms of GPIIb whi constitute the Bak polymorphism.
Another object of the present invention is to provi methods for diagnosing and treating clinical syndromes related a GPIIb-related immune response.
In achieving these objects, there has been provided, accordance with one aspect of the present invention, oligonucleotide probe molecule that hybridizes to a portion the GPIIb gene, which portion includes a nucleotide correspondi to nucleotide 2662 of GPIIb cDNA, where the molecule hybridiz to the portion in question when nucleotide 2662 is guanylate, f one type of allele-specifc probe, or thymidylate for anoth type. In a preferred embodiment, the oligonucleotide probe of t present invention is is between about ten and thirty bases length.
In accordance with another aspect of the prese invention, a kit for typing platelet Bak alloantigens has be provided that comprises (a) a receptacle containing a solution of a labeled oligonucleotide probe that distinguishes an allele of a platelet Bak alloantigen from other alleles, or
(b) a receptacle containing a solution of an antibody that discri inately binds a Baka allele or a Bakb allele of GPIIb, where the antibody
(i) recognizes a polypeptide molecule encoded by a nucleotide sequence encoding at least amino acid 843 of GPIIb and (ii) binds either the Baka allele or the Bakb allele of GPIIb, or
(c) a receptacle containing a solution of a endonuclease recognizing a cleavage site that distinguishes nucleotide sequence of an allele of a platelet Bak alloantige from other alleles, and
(d) means for amplifying DNA that comprises at least portion of a GPIIb gene or GPIIb cDNA, where the portion i question includes a nucleotide corresponding to nucleotide 266 of GPIIb cDNA.
There has also been provided, in accordance with anothe aspect of the present invention, a method of typing glycoprotei lib, comprising the steps of (A) synthesizing cDNA from huma platelet mRNA of an individual; (B) amplifying the cDNA t produce amplified cDNA; and then (C) analyzing the amplified cDN to determine Bak alloantigen phenotype for that individual. I one preferred embodiment, the further comprises synthesizing cDN from human platelet mRNA of a second individual, repeatin aforementioned steps (B) and (C) on the cDNA of secon individual, and thereafter discriminating between the first an second individuals based on the alloantigen phenotype.
In another preferred embodiment, step (C) comprises the steps o (i) digesting the amplified cDNA with a restriction endonucleas recognizing a cleavage site that distinguishes a nucleotid sequence of a first Bak allele from another Bak allele; and the (ii) analyzing the cDNA fragments to determine the Ba alloantigen phenotype.
In accordance with yet another aspect of the presen invention, a method of typing platelet Bak membrane glycoprotein has been provided that comprises the steps of (A) obtainin genomic DNA from an individual and (B) analyzing the genomic DN to determine a platelet Bak alloantigen phenotype. In preferred embodiment, step (B) comprises
(i) digesting the genomic DNA with a restriction endonuclease produce DNA fragments; thereafter (ii) hybridizing the DN fragments with a labeled, allele-specific oligonucleotide prob that distinguishes a nucleotide sequence of an allele of platelet Bak alloantigen from other alleles; and then (iii analyzing the probe that has hybridized to the DNA fragments i order to determine the Bak alloantigen phenotype.
In accordance with still another aspect of the presen invention, there has been provided a method of typing platelet with respect to GPIIb that comprises the steps of (A) obtainin genomic DNA from an individual, (B) amplifying the genomic DNA t produce amplified genomic DNA and
(C) analyzing the amplified genomic DNA to determine a platele Bak alloantigen phenotype. In a preferred embodiment, step (C comprises of
(i) hybridizing the amplified genomic DNA with a labeled, allele specific oligonucleotide probe that distinguishes a nucleotid sequence of a first Bak allele from that of another Bak allele and then
(ii) analyzing the probe that has hybridized to the amplifie genomic DNA to determine said alloantigen phenotype. In anothe preferred embodiment, step (C) comprises
(i) hybridizing the amplified genomic DNA with a pair o oligonucleotide probes to form a construct, wherein a first prob of the pair of probes is labeled with a first label and the othe probe is labeled with a second label, such that the first labe is distinguishable from the second label, and the probe hybridize adjacently to each other at a nucleotide tha distinguishes a Bak allele from another Bak allele; thereafter

(ii) reacting said construct with a ligase in a reactio medium; and then
(iii) analyzing said reaction medium to detect th presence of a ligation product comprising the first probe th said second probe.
A polypeptide molecule is further provided, in accordanc with another aspect of the present invention, that comprises a amino-acid sequence that corresponds to a tetramer fragment of GPIIb, wherein the fragment comprises amino acid 843 of GPIIb and wherein the molecule is not GPIIb itself. Preferably, the polypeptide molecule is between four and fifty amino-acid residues in length. In addition, it is preferred that the polypeptide molecule is itself immunogenic or is attached to a immunogenicity-imparting carrier, forming another molecule of the present invention.
According to another aspect of the present invention, an antibody is provided that distinguishes the Baka form of GPIIB antigen from the Bakb form, where the antibody recognizes a polypeptide sequence that comprises at least amino acid 843 of GPIIb. The antibody can be a monoclonal antibody produced by a method comprising the steps of (A) immunizing a mammal with an antigenic molecule comprising a polypeptide as described above, then (B) removing lymphocytes from the mammal, (C) fusing the lymphocytes with mammalian myeloma cells to form hybridoma cells, (D) culturing the hybridoma cells and thereafter (E) selecting, isolating and cloning hybridoma cells secreting monoclonal antibodies that distinguish between the Baka and Bakb forms of GPIIb.
A method is also provided, pursuant to another aspect of the present invention, for treating post-transfusion purpura or neonatal alloimmune thrombocytopenia, comprising the step of administering to an individual a formulation comprised of a peptide in a pharmacologically effective concentration and a physiologically-compatible carrier therefor, where the individual (i) suffers from post-transfusion purpura or is the mother of fetus at risk for developing NATP and (ii) has anti-Baka or anti Bakb antibodies, said peptide binding an antibody selected fro the group consisting of an anti-Baka antibody and an anti-Bak antibody.
In accordance with yet another aspect of the presen invention, an isolated DNA molecule has been provided tha comprises a nucleotide sequence corresponding to a portion of th GPIIb gene that includes a nucleotide corresponding to nucleotid 2622 of GPIIb cDNA, wherein the molecule is not coincident wit the GPIIb gene.

Other objects, features and advantages of the presen invention will become apparent from the following detaile description. It should be understood, however, that the detaile description and the specific examples, while indicating preferre embodiments of the invention, are given by way of illustratio only, since various changes and modifications within the spiri and scope of the invention will become apparent to those skille in the art from this detailed description.

Brief Description of the Drawings

Figure 1 is a diagrammatic representation of the GPII mRNA molecule. The locations of two oligonucleotide primers use for PcR amplification are also shown.
Figure 2 shows autoradiographs of electrophoretic gel used in the sequence analysis of amplified GPIIb cDNA, derive from both a Baka homozygous individual and a Bakb homozygou individual. A segment of the autoradiograph, encompassing base 2615 to 2626 indicates a single base substitution of a thymin (T) (Bakb allele) for a guanine (G) (Baka allele) at base 2622. (See below regarding the number of nucleotides herein.)
Figure 3 is a photograph of the results of an analysi of Bak phenotype by allele-specific oligonucleotid hybridization. Bases 1988 to 2821 were enz^matically amplifie from platelet RNA from nine individuals of known Bak phenotype. An allele-specific oligonucleotide (Probe A) hybridized to DN from Baka homozygous individuals (wells 1-4) . A second allele specific oligonucleotide (Probe B) hybridized to DNA from Bak homozygous individuals (wells 5-7) . Heterozygous individual were positive with both probes (wells 8 and 9) .
Figure 4 is the amino acid sequence of the region o GPIIb responsible for the Bak polymorphism.

Detailed Description of the Preferred Embodiments

It has been discovered that a single nucleotide of GPIIb is responsible for the Bak polymorphism. In light of this discovery, manipulation of nucleic-acid molecules derived from platelets can be effected to provide for the analysis of alloantigen phenotypes, for the generation of peptides encoded by these molecules, and for the use of such peptides in diagnosis and therapy relating to a human platelet Bak polymorphism. Nucleic-acid molecules utilized in these contexts may be amplified, as described below, and generally include RNA, genomic DNA and cDNA derived from RNA.
Although the generation of cDNA from platelet or red blood cell mRNA was previously thought to be unfeasible, a ne approach has been discovered for examining platelet mRNA fro single individuals. As described in copending U.S. applicatio serial
No. 07/343,827, the contents of which are hereby incorporated b reference, is been found that mRNA can be obtained from platelet as well as red blood cells in quantities sufficient fo isolation, cDNA generation, and amplification. By generating an amplifying cDNA produced from mRNA of a number of individuals o known platelet allotypes, the nucleotide sequence variations tha exist in the genes that express alloantigen determinants can b ascertained. Furthermore, by isolating and amplifying mRNA fro a number of individuals of known allotype, it is possible, pursuant to the present invention, to identify phenotype-specifi nucleotide sequence variations in corresponding genes.
To obtain amplified cDNA from platelet mRNA, mRNA derive via conventional methods, see, e.g., MANIATIS, ET AL. , MOLECULA CLONING: A LABORATORY MANUAL 187-210 (Cold Spring Harbou Laboratory, 1982) , from platelets can be converted to cDNA an then enzymatically amplified to produce microgram quantities o platelet-specific cDNA. This amplification is preferabl accomplished via the "polymerase chain reaction" (PcR) metho disclosed by U.S. patent Nos. 4,683,195 and 4,800,159, th respective contents of which are hereby incorporated b reference.

More specifically, in the process of generating an amplifying cDNA encoded by the isolated platelet mRNA oligonucleotide primer pairs can be constructed that allo enzymatic amplification of a cDNA segment obtained from an mRN molecule that encodes an amino-acid sequence defining th polymorphism. The corresponding, isolated cDNAs can then b analyzed to determine the molecular basis of observed phenotypi differences. The ability to compare directly the nucleotide an corresponding amino-acid sequences of genes encoding alleles o alloantigens is made possible by (1) the discovery that cDNA ca be generated and amplified successfully from platelet mRNAs an (2) the determination of a nucleotide sequence of a glycoprotei which is thought to be polymorphic.
The molecular description of polymorphisms associate with platelet alloantigens can be provided by analyzing amplifie cDNA, generated from platelet mRNA, according to one of th following methods: differential restriction endonucleas digestion (DRED) , allele-specific oligonucleotide probing (ASOP) and ligase-mediated gene detection (LMGD) . Additional method of analysis would also be useful in this context, such a fluorescence resonance energy transfer (FRET) as disclosed b Wolf, et al., Proc. Nat. Acad. Sci. USA 85: 8790-94 (1988), th contents of which are hereby incorporated by reference.
DRED analysis is accomplished in the following manner If conditions occur including (1) a particular amplified cDN segment contains a sequence variation that distinguishes a allele of a polymorphism and (2) this sequence variation i recognized by a restriction endonuclease, then the cleavage b the enzyme of a particular polynucleotide segment can be used t determine the alloantigen phenotype. In accomplishing thi determination, amplified cDNA derived from platelet mRNA i digested and the resulting fragments are analyzed by size. Th presence or absence of nucleotide fragments, corresponding to th endonuclease-cleaved fragments, determines which phenotype i present.
Thus, a guanine(G) < > thymine(T) polymorphism at bas

2622 is revealed by examination of the nucleotide sequenc contained in cDNA generated from mRNA derived from Bakb homozygous vs. Baka-homozygous individuals. (Throughout this description, the numbering of nucleotides in mRNAs and cDNAs is with reference to the cDNA sequence disclosed by Poncz, et al., J. Biol. Chem. 262: 8476 (1987), the contents of which article are hereby incorporated by reference. A nucleotide of genomic DNA that corresponds to a particular nucleotide in a cDNA is designated by the number of the cDNA nucleotide.) This single nucleotide substitution results in the creation of a unique restriction enzyme cleavage site for the restriction endonuclease Fokl. By utilizing a restriction endonuclease with the selectivity of Fokl or an isoschizimer thereof to discriminate between these two polymorphic sequences, the phenotypes of individuals can be determined in the above-described manner. Sequence analysis of the resulting restriction fragments demonstrates that the Bakb form of GPIIb mRNA contains the codo AGC, encoding serine at position 843 of the known GPIIb amino-acid sequence, in place of an ATC codon coding for isoleucine a position 843 in the Baka form. (The designation of amino aci residues in this regard follows the numbering system of Poncz, e al., incorporated above by reference.)
In ASOP analysis according to conventional methods, oligonucleotide probes are synthesized that will hybridize, unde appropriate annealing conditions, exclusively to a particula amplified cDNA segment that contains a nucleotide sequence tha distinguishes one allele from other alleles of a platele membrane glycoprotein. Such a probe would be discernably labele so that when it hybridizes to the allele-distinguishing cDN segment, it can be detected and the specific allele thu identified.
For example, an oligonucleotide probe can b synthesized, in accordance with the present invention, that wil hybridize to a cDNA segment, derived from GPIIb mRNA, tha contains the base thymine at polymorphic nucleotide 2622
(nucleotide = thymidylate) . Alternatively, an oligonucleotid probe of the present invention will hybridize what the cDN segment contains the base guanine at nucleotide 2622 (nucleotid = guanylate) . These allele-specific probes can be appropriatel labeled and added to the generated cDNA segments under annealin conditions, such that one of the allele-specific probe hybridizes and can be detected, thereby identifying the specifi BAka or Bakb allele. In accordance with conventional procedure the design of an oligonucleotide probe according to the presen invention preferably involves adjusting probe length t accommodate hybridization conditions (temperature, ioni strength, exposure time) while assuring allele-specificity. length of ten to thirty nucleotides is typical.
In the course of the third method of analysis, LMGD, a disclosed by Landegren, et al., Science 241: 1077-80 (1988), th contents of which are hereby incorporated by reference, a pair o oligonucleotide probes are synthesized that will hybridiz adjacently to each other, i.e., to a cDNA segment unde appropriate annealing conditions, at the specific nucleotide tha distinguishes one allele from other alleles of a platele membrane glycoprotein. Each of the pair of specific probes i labeled in a different manner, and, when both probes hybridize t the allele-distinguishing cDNA segment, the probes can be ligate together by the addition of a ligase.
When the ligated probes are separated and isolated fro the cDNA segments, both types of labeling can be observe together on a Northern blot when analyzed by conventiona procedures, confirming the presence of the allele-specifi nucleotide sequence. Where the above-described pair o differently labeled probes bind to a nucleotide sequenc containing a distinguishing nucleotide of a different allele, th probe pair is not ligatable and, after the probes are isolate from the cDNA segments, each type of labeling is observed to b separate from the other label type.
An exemplary LMGD analysis, according to the presen invention, entails the use of a pair of oligonucleotide probes, wherein one probe is radioactively 32P-labeled and the other prob is biotin-labeled. Under appropriate conditions, the pair o probes adjacently hybridizes to a cDNA segment at a nucleotid corresponding to nucleotide 2622 of GPIIb. The biotin labele probe hybridizes to nucleotides 2602-2622 of GPIIb, wherei nucleotide 2622 contains a thymine, which distinguishes the Bak allele. The 32P-labeled probe hybridizes nucleotides 2623-2633 - 12 - of GPIIb and, therefore will hybridize adjacently to the biotin- labeled probe. These probes are then added under annealing conditions such that they hybridize adjacently to each other spanning nucleotides
5 2602-2633 of GPIIb. The biotin labeled probe is detected by the binding of the compound strepavidin after hybridization and the P32-labeled probe is detected by autoradiography, according to conventional procedures.
When the Bakb allele sequence is present in the amplified

10 cDNA, then the addition of a ligase will result in the biotin labeled probe being covalently bound to the 32P-labeled probe. The ligation is possible, because the ends of the probes that are adjacent to each other (hybridized to nucleotides (2622 and 2633) are both hybridized to the cDNA. In the case where these two

15 probes hybridize to the Bakb allelic form of the cDNA sequence, the biotin-labeled probe end at nucleotide 2622 is not hybridized appropriately, preventing the ligation step from occurring. When this pair of probes binds completely to the Bakb allele sequence, therefore, the probes are ligated and when the probes are

20 separated from the Bakb sequence and exposed so as to be detected, both the biotin/strepavidin and the 32P labeling are present together. When the Baka allele sequence is hybridized, on the other hand, the probes cannot be ligated, and the biotin/strepavidin- and 3p-labeling are observed separately. In

25 this manner, the Bakb and Baka alleles sequences and corresponding phenotype can be distinguished.
Alternatively, DRED, ASOP and LMGD or other suitable methods of analysis, such as FRET, can be used with genomic or amplified-genomic DNA to distinguish platelet membrane

30 glycoprotein Bakb from Baka, starting with any nucleated cell sample, obtained from an individual, from which DNA can be isolated in sufficient quantities for analysis. Amplified genomic DNA would be amplified from isolated genomic DNA in the same manner as described above for cDNA. Once a tissue sample,

35 such as cells scraped from the inside of an individual's cheek, has been obtained, genomic DNA isolated by conventional procedures can be analyzed directly per se or amplified prior t analysis.

The foregoing description of the three types of analysi would apply to the use of genomic DNA or amplified-genomic DNA with the term "cDNA" being replaced with "genomic or amplifie genomic DNA." One difference in the analysis of genomic DNA o amplified genomic DNA is that the GPIIb sequence used fo designing a suitable oligonucleotide probe might have to includ any intronic sequences, which would not be present in the cDNA o GPIIb, that were near or adjacent to the nucleotide tha determines the Bak phenotype.
In general, the presence of intronic sequences near th phenotype-determining nucleotide can be ascertained by sequenc analysis of genomic DNA, accomplished via Maxam-Gilbert o another conventional technique. Sequence information on th region of genomic DNA encompassing an exon that encodes th polymorphism can be used to design appropriate oligonucleotides such that a genomic DNA-based PcR could be performed. Th resulting amplified products can then be assessed for alloantige phenotype, in accordance with the present invention, by means o any of the above-described diagnostic methods.

The polymorphic nucleotide which distinguishes the above described GPIIb alleles is located (see asterisk) in an exo shown below with flanking genomic segments. In accordance wit convention, the following is the coding sequence of the genomi DNA; the GPIIb amino-acid residues encoded by the exon are als shown, with conventional acronyms used (v for valine, d fo aspartic acid, etc.):
(end of (intron>
an exon)

v d w g
(exon starts at underscored "AG")

l p i p s p s p i h p a h h k r d

r r q i f l p e p e q p s r l q d

p v 1 v
(exon ends at underscored "GT")

(Sequence data provided by Dr. Mortimer Poncz, The
Children's Hospital of Philadelphia.) More
generally, the primers used for PcR amplification
should be positioned, relative to the exon which
contains the polymorphic nucleotide, so that the
amplified region encompasses that nucleotide, which
corresponds to base 2622 of the GPIIb cDNA. For
example, the solid bar and striped bar above denote,
respectively, a sequence of a first primer and the
complementary sequence of a second primer which are suitable for genomic amplification as described herein.
The ability to perform DNA-typing analysis for determination of Bak phenotypes, pursuant to the present invention, has a number of useful clinical applications, including but not limited to those involving determination of the Bak alloantigen phenotype of an individual, and the diagnosis and treatment of a pathological immune response (or potential response) involving foreign alloantigens or antibodies. In accordance with the present invention, alloantigen phenotyping can be effected by the generation of amplified genomic DNA or amplified cDNA from platelet mRNA, permitting diagnosis of individuals for the purpose of treating or preventing pathological immune responses.
Once the nucleotide-sequence variations specific for each allelic form of the alloantigens of a given class are determined, other conventional methods can be employed, through the use of genomic

DNA or platelet RNA, to perform the same type of diagnosis on other individuals. These methods would include, but not are limited to, allele-specific nucleotide probing and ligase-mediated gene detection, as previously described.
Diagnostic kits can also be used, in accordance with the present invention, for the determination and diagnosis of alloantigen phenotypes via the procedures described herein. Such a kit can include, inter alia. antibodies or antibody fragments to an antigenic determinant expressed by either of the above-described Baka- and Bakb-encoding sequences, which antibodies would react with the blood sample of an individual so as to indicate whether that individual has a Baka or Bakb phenotype.

Alternatively, all the reagents required for the detection of nucleotide (s) that distinguish the Bak alloantigens, by means described herein, can be provided in a single kit that uses isolated genomic DNA or platelet mRNA from an individual. Containing a labeled probe that distinguishes, for example, nucleotide 2622 of GPIIb, such a kit can be utilized for Bak alloantigen phenotyping.
A further beneficial use of the nucleotide sequences that distinguish the Baka allele from the Bakb allele is to obtain or synthesize the respective expression product, in the form of a polypeptide, encoded by these nucleotide sequences. These polypeptides can be used to generate antibodies for diagnostic and therapeutic uses, for example, with regard to pathological conditions such as PTP or NATP.
A polypeptide within the present invention which can be used for the purpose of generating such antibodies preferably comprises an amino-acid sequence that corresponds to (i.e., is coincident with or functionally equivalent to) a four-residue (tetramer) fragment of the GPIIb molecule that includes amino acid 843. When the latter amino acid is serine, the polypeptide can be used, as described above, to produce antibodies that specifically bind the Bakb form of GPIIb; when it is isoleucine, antibodies can be obtained that particularly recognize the Baka form. The class of polypeptides thus defined, in accordance with the present invention, is not intended to include the GPIIb molecule itself, but does encompass fragments of the molecule as well as synthetic polypeptides meeting the aforementioned definition.
Although the length of a polypeptide within this class is not critical, the requirement for immunogenicity may require that the polypeptide be attached to a immunogenicity-imparting carrier, e.g., a particulate carrier like a liposome or a soluble macromolecule (protein or polysaccharide) with a molecular weight in the range of about 10,000 to 1,000,000, or be administered with an adjuvant, such as complete Freund's adjuvant. For artificial polypeptides, as distinguished from GPIIb fragments, maximum length is determined largely by the limits of techniques available for peptide synthesis, say, about fifty amino acids. Thus, a synthetic polypeptide of the present invention is preferably between four and about fifty amino acids in length.

In this context, the term "antibody" encompasses monoclonal and polyclonal antibodies.

Such an antibody can belong to any antibody class

(IgG, IgM, IgA, etc.). For monoclonal antibody

(Mab) production, one generally proceeds by isolating lymphocytes and fusing them with myeloma cells, producing hybridomas. The cloned hybridomas are then screened for production of antibodies the bind preferentially to either the Baka form or the

Bakb form of GPIIb. "Antibody" also encompasses fragments, like Fab and F(ab')2, of anti-Baka or anti-Bakb antibodies, and conjugates of such fragments, and so-called "antigen binding proteins"

(single-chain antibodies) which are based on anti- Baka or anti-Bakb antibodies, in accordance, for example, with U.S. patent No. 4,704,692, the contents of which are hereby incorporated by reference. Human alloantisera currently used for serological typing are specifically excluded from this definition. Alternatively, Mabs or a fragment thereof within the present invention can be produced using conventional procedures via the expression of isolated DNA which codes for variable regions of such an Mab in host cells like E___ colif see, e.g.,

Ward, et al., Nature, 341:544-546 (1989), or transfected murine myeloma cells. See Gillies, et al., Biotechnol . 7: 799-804 (1989); Nakatani, et al., Biotechnol . 7: 805-10 (1989).
Diagnostic applications of these antibodies are exemplified, according to the present invention, by the use of a kit containing an anti-Baka or an anti-Bak13 antibody which undergoes a reaction with a sample of an individual's blood to determine a Baka or Bakb platelet phenotype. Such a reaction involves the binding of anti-Baka antibody to Baka antigen or the binding of anti-Bakb antibody to Bakb antigen. The observation antibody-antigen complex in a blood sample would indicate a positive result. A kit of this sort could be used to diagnose, or to help prevent, the occurrence of pathological conditions like PTP or NATP.
A polypeptide of the present invention that is recognized specifically by anti-Baka or anti-Bakb antibodies can be used therapeutically. Thus, antibodies raised against such a polypeptide can employed in the generation, via conventional methods, of anti-idiotypic antibodies (that is, antibodies that bind an anti-Baka or anti-Bakb antibody), e.g., by the use of hybridomas as described above. See, for example, U.S. patent

No. 4,699,880, the contents of which are hereby incorporated by reference. Such anti-idiotypic antibodies would bind endogenous or foreign anti-Bak antibodies in the blood of an individual, thereby to treat or prevent pathological conditions associated with an immune response to a "foreign" Bak alloantigen. Alternatively, a polypeptide within the present invention can be administered, with a physiologically-compatible carrier, to achieve the same qualitative effect, namely, the selective reduction or elimination of circulating anti-Bak antibodies from a patient suffering or at risk from an immune response.
The present invention is further described below by reference to the following, illustrative examples. Used in the examples were platelet samples from four homozygous Baka individuals, three homozygous Bakb individuals, and two individuals who were heterozygous for the Bak allotype. The respective phenotypes of all the test subjects had been identified using well-characterized anti-Baka and anti-Bakb human alloantisera.

Platelet RNA from a panel of nine normal. volunteers, including four Baka a, three Bak bb and two Bak ab individuals, was prepared according to the procedure developed by Chomczynski and Sacchi, Anal. Biochem. 162:156 (1987), except that the final

RNA pellet was subjected to one additional phenol/chloroform extraction and ethanol precipitation necessary to achieve reproducible gene amplification of platelet cDNA. Baka and Bakb phenotype was assessed using well-characterized human alloantisera in a standard antigen capture assay, see Furihata, et al., J. Clin. Invest.

80:1624 (1987); Chomczynski and Sacchi, Anal.

Biochem. 162:156 (1987). The C-terminal end of the GPIIb heavy and light chain message from base 1988 to 2821 was selected for sequence analysis and comparison, and two 24-base oligonucleotide primers flanking 833 base pairs of this region were synthesized on a Gene Assembler (Pharmacia Fine Chemicals, Piscataway, NJ) .
The anti-sense primer
(5'-CAGGAAGGCCAGCACCGTGACCATG-3') from base 2821 to

2797 was used to prime the synthesis of cDNA from platelet RNA as previously described (Newman, et al., J. Clin. Invest. 82:739 (1988); Newman, et al . ,

J. Clin. Invest. 83:1778 (1989). The second strand was generated by the sense primer

(5'GAGCTGCAGATGGACGCAGCCAAC-3') from base 1988 to

2011 during the first round of PcR. Amplification was carried out in a DNA Thermal Cycler (Perkin- Elmer Cetus, Norwalk, CT) programmed to permit denaturation at 94° C for on 1/2-minute, annealing at 50° C for one 1/2-minute, and chain extension at 72° C for three minutes. The reaction was allowed to proceed for 30 cycles followed by a final incubation at 72° C for seven minutes to allow completion of strand synthesis.

PcR samples were analyzed on 1.8% Seakem GTG agarose gels (FMC BioProducts, Rockland, ME) , and the appropriate bands were excised and recovered by electroelution. The plasmid vector pGEM-5Zf

(Promega Biotech, Madison, WI) was prepared for ligation by restriction digestion with Eco RV (New England Biolabs, Beverly, MA) to yield blunt ends, and ligated to purified amplification product, followed by transformation into E___ coli strain NM522 competent cells (Stratagene Cloning Systems, San Diego, CA) . Two clones representing each Bak homozygous phenotype were selected for direct sequence analysis of the plasmid DNA by the dideoxy sequencing method using T7 DNA polymerase (USB,

Cleveland, Ohio USA) . Four 24 or 25 base oligonucleotides were synthesized and used as sequencing primers.
The results (shown in Figure 2) demonstrated that a single nucleotide difference was observed between the Bak8a and Bakb/b clones at base 2622. Analysis of the cDNA derived from the Baka/a individual revealed that thymine was present at this position, whereas guanine was substituted in this position in the Bakb/b cDNA. This resulted in a substitution of a serine for an isoleucine at amino acid residue 843.

Amplified cDNA from four individuals with Baka/a phenotype, three with Bakb , and two heterozygous for Bak was subjected to hybridization with 13-base allele-specific oligonucleotides (ASO) . Probe A (TGCCCATCCCCAG) corresponds to the published sequence of GPIIb (Poncz, et al., J. Biol. Chem. 262(18) :8476 (1987)) from base 2616 to 2628, while

Probe B (TGCCCAGCCCCAG) differs only in the middle base, a G instead of a T, and corresponds to a single base difference observed in the region sequenced. The probes (200ng) were end-labeled with digoxigenin-11-dUTP (Boehringer Mannheim,

Indianapolis, IN) in 25 μl 100 mmol/L potassium cacodylate, 2 mmol/L CoCl2, 0.2 mmol/L DTT, pH 7.2 containing 1 U terminal transferase (Boehringer Mannheim, Indianapolis, IN) , and the probes were used for hybridization without purification.
Amplified DNA was used directly for blotting or, in some cases, appropriate bands were recovered from agarose gels using Gene Clean (Bio 101, LaJolla, CA) . The samples were eluted in 20 μl water, diluted 1/10,000, and 10 μl was used for reamplification using the same probes and PcR conditions. Amplified or reamplified DNA was denatured in 0.25 N NaOH, 1.5 mol/L NaCl at room temperature for 15 minutes. Each sample was divided between two wells of a Minifold dot blot apparatus

(Schleicher and Schuell, Keene, NH) and transferred to Magnagraph nylon membrane (MSI, Westboro, MA) by vacuum suction. The filter was exposed to UV irradiation (Fotodyne, New Berlin, WI) for 5 minutes followed by baking at 80° C for 15 minutes. T h e membrane was prehybridized in 5X Denhardt's, 5X SSC, 10 mmol/L EDTA, 10 mmol/L Na-HP04, pH 7 at 68° C for one hour, and then cut into two strips which were hybridized to either Probe A or Probe B in 4 mis 10X Denhardt's 5X SSC, 5mmol/L EDTA, 7% SDS, 50 ug/ml

Salmon sperm DNA, 20 mmol/1 Na2HP04, pH 7 at 42° C overnight. The filters were washed in 2 changes 6X SSC for 30 minutes each at room temperature followed by 2 changes of 3 mol/L tetra ethylammonium chloride (Aldrich Chemical, Milwaukee, WI) , 2 mmol/L EDTA, 1% SDS, 50 mmol/L Tris, pH 8 for 20 minutes each at 42° C. Positive hybridizations using The Genius kit (Boehringer Mannheim, Indianapolis, IN) which employs an alkaline phosphatase-conjugated antidigoxigenin antibody, according to the manufacturer' s directions.
The results, shown in Figure 3, demonstrated that Probe A was positive with the four Baka/a homozygous individuals, Probe B was positive with the three Bak b homozygous individuals, and both probes were positive with amplified DNA from the two heterozygous individuals analyzed.