Human platelet alloantigens

Simultaneous genotyping for human platelet antigen systems and HLA-A and HLA-B loci by targeted next-generation sequencing

In order to treat the alloimmunization platelet transfusion refractoriness (PTR), human leukocyte antigen (HLA)-type and/or human platelet antigen (HPA)-type matched platelets between donors and patients are usually used. Therefore, genotyping of HLA-A and HLA-B loci, as well as HPA systems, for donors and patients, is of great significance. However, there is a rare report of genotyping for HLA-A and HLA-B loci as well as HPA systems at the same time. In this study, a high-throughput method for simultaneous genotyping of HLA-A and HLA-B loci, as well as HPA genotyping, was developed. A RNA capture probe panel was designed covering all exon sequences of the GP1BA, GP1BB, ITGA2, CD109, ITGB3, and ITGA2B genes and HLA-A and HLA-B loci. The HLA-A, HLA-B, and 34 HPA systems were genotyped using a targeted next-generation sequencing (NGS) method. The genotypes of the HLA-A and HLA-B loci, as well as the HPA, were assigned based on the nucleotides in the polymorphism sites. Using the NGS method, 204 unrelated blood specimens were successfully genotyped for all 34 HPA systems as well as HLA-A and HLA-B loci. The accuracy of the NGS method was 100%. Only HPA-2, HPA-3, HPA-5, HPA-6w, HPA-15, and HPA-21w showed polymorphism with frequencies of 0.9412, 0.6863, 0.9853, 0.9779, 0.4314, and 0.9951 for a allele, respectively. Thirty-two single nucleotide variants (SNVs) were detected. Of them, 12 SNVs can lead to amino acid change. HLA-A*11:01 and HLA-B*46:01 are the most common alleles for HLA-A and HLA-B loci. A targeted next-generation sequencing method for simultaneously genotyping HPA systems and HLA-A and HLA-B loci was first established, which could be used to create a database of HLA-typed and/or HPA-typed unrelated donors.

Platelet CD36 deficiency is present in 2.6% of Arabian individuals and can cause NAIT and platelet refractoriness

BACKGROUND

CD36 isoantibodies are capable of inducing neonatal alloimmune thrombocytopenia (NAIT) and platelet refractoriness. As to now the CD36 type I deficiency has been reported in East Asian and African individuals. However, it is virtually unknown in Caucasians. The aim of this study was to display the prevalence of the CD36 deficiency within parts of the Arabian population in Germany. Secondly, we are presenting the case of a newborn suffering from NAIT which was induced by CD36 antibody.

METHODS

Platelet (p) CD36 was determined by flow cytometry on 1328 samples mainly from individuals of Arabian origin and a family with a neonate affected by NAIT. DNA sequencing was performed on all pCD36-negative samples.

RESULTS

Thirty-five (2.64%) of all donor samples were pCD36 negative, 19 (1.43%) had a weak expression. Including only individuals from the Arabian peninsula, frequencies were 3.39% and 1.75%, respectively. CD36 type I deficiency on both platelets and monocytes combined with a CD36 isoantibody were detected in the mother of the NAIT baby. The baby was successfully transfused with two HPA-unselected platelet concentrates. In case of need, two platelet units with a weak pCD36 expression were on hand. A total of 45 different CD36 mutations were detected within pCD36-negative individuals, some being homozygous, most of them only present on one allele.

CONCLUSION

The CD36-negative phenotype is present in a significant number of individuals of Arabian origin and enables CD36 isoimmunization in NAIT or refractoriness. Blood transfusion services should be aware of such cases.

[Polymorphism of human platelet antigens in Tunisian population: Clinical and anthropological interests]

OBJECTIVES

Human Platelet Antigens (HPA) are of considerable interest in obstetric transfusion medicine and anthropological genetics. This study aims to provide clinicians with a detailed database of HPA antigenic variants, which allows them to estimate the probability of allo-immunisation of each antigen. In addition, it aims to make an interethnic comparison of the Tunisian population with other populations.

METHODS

The target population consists of 324 healthy and unrelated Tunisian blood donors recruited from the National Blood Transfusion Center in Tunis. DNA extraction was performed by the Salting Out method and molecular genotyping was performed by the PCR-SSP technique. The statistical analysis was performed using two approaches: manual calculation and computerized calculation. Phylogenetic trees were constructed through the use of Standard Genetic Distances that were calculated from allelic frequencies.

RESULTS

With the exception of the HPA-4 system, statistical analysis showed that all HPA systems are polymorphic especially the two systems HPA-3 and HPA-15. The inter-ethnic analysis showed that Tunisians are closer to North Africans and Caucasians than Sub-Saharan and Asian populations, which shows genetic mixing between Tunisians, Arabs, Europeans and Africans.

CONCLUSION

The results of this study could be exploited to prepare a ready-to-use genotyping plate dedicated to HPA antigens, with the aim of ensuring better management, especially for polytransfused patients.

Aplastic anemia during pregnancy: a review of obstetric and anesthetic considerations

Aplastic anemia is a hematologic condition occasionally presenting during pregnancy. This pathological process is associated with significant maternal and neonatal morbidity and mortality. Obstetric and anesthetic management is challenging, and treatment requires a coordinated effort by an interdisciplinary team, in order to provide safe care to these patients. In this review, we describe the current state of the literature as it applies to the complexity of aplastic anemia in pregnancy, focusing on pathophysiologic aspects of the disease in pregnancy, as well as relevant obstetric and anesthetic considerations necessary to treat this challenging problem. A multidisciplinary-team approach to the management of aplastic anemia in pregnancy is necessary to coordinate prenatal care, optimize maternofetal outcomes, and plan peripartum interventions. Conservative transfusion management is critical to prevent alloimmunization. Although a safe threshold-platelet count for neuraxial anesthesia has not been established, selection of anesthetic technique must be evaluated on a case-to-case basis.

Current trends in platelet transfusions practice: The role of ABO-RhD and human leukocyte antigen incompatibility

Platelet transfusions have contributed to the revolutionary modern treatment of hypoproliferative thrombocytopenia. Despite the long-term application of platelet transfusion in therapeutics, all aspects of their optimal use (i.e., in cases of ABO and/or Rh (D incompatibility) have not been definitively determined yet. We reviewed the available data on transfusion practices and outcome in ABO and RhD incompatibility and platelet refractoriness due to anti-human leukocyte antigen (HLA) antibodies. Transfusion of platelets with major ABO-incompatibility is related to reduced posttransfusion platelet (PLT) count increments, compared to ABO-identical and minor, but still are equally effective in preventing clinical bleeding. ABO-minor incompatible transfusions pose the risk of an acute hemolytic reaction of the recipient that is not always related to high anti-A, B donor titers. ABO-identical PLT transfusion seems to be the most effective and safest therapeutic strategy. Exclusive ABO-identical platelet transfusion policy could be feasible, but alternative approaches could facilitate platelet inventory management. Transfusion of platelets from RhD positive donors to RhD negative patients is considered to be effective and safe though is associated with low rate of anti-D alloimmunization due to contaminating red blood cells. The prevention of D alloimmunization is recommended only for women of childbearing age. HLA alloimmunization is a major cause of platelet refractoriness. Managing patients with refractoriness with cross-matched or HLA-matched platelets is the current practice although data are still lacking for the efficacy of this practice in terms of clinical outcome. Leukoreduction contributes to the reduction of both HLA and anti-D alloimmunization.

High-throughput simultaneous genotyping of human platelet antigen-1 to -16 by using suspension array

BACKGROUND

Comprehensive and accurate detection of human platelet antigens (HPAs) plays a significant role in diagnosis and prevention of the platelet (PLT) alloimmune syndromes and ensuring clinical safety of patients undergoing PLT transfusion. The majority of the available methods are incapable of performing high-throughput simultaneous detection of HPA-1 to -16, and the accuracy of many methods needs to be further enhanced.

STUDY DESIGN AND METHODS

We have developed a new HPA-genotyping method for simultaneous detection of HPA-1 to -16 based on suspension array technology. A total of 216 samples from Chinese Han donors in Xi'an were genotyped using the developed method, and all the samples again were genotyped using polymerase chain reaction (PCR) sequence-based typing (PCR-SBT), which is considered the gold standard.

RESULTS

All 216 samples were successfully genotyped for HPA-1 to -16 using both our method and PCR-SBT. Results showed that the genotype and allele frequencies obtained using our method were fully consistent with those obtained using PCR-SBT.

CONCLUSION

Our method provides accurate, high-throughput, and simultaneous genotyping of HPA-1 to -16 and will serve as the foundation for large-scale clinical genotyping of HPAs and for the establishment of an HPA-typed PLT donor registry.

Human platelet alloantigens HPA-1, HPA-2, and HPA-3 polymorphisms associated with extent of severe coronary artery disease

The contribution of human platelet antigen (HPA)-1 (GPIIb/IIIa), HPA-2 (GPIb/IX), and HPA-3 (GPIIb/IIIa) polymorphisms to the risk of coronary artery disease (CAD) was investigated in 341 CAD patients and 316 matched control subjects. HPA genotyping was performed by PCR-SSP. Regression analysis was employed in assessing the contribution of these variants to CAD risk. The frequency of HPA-1b (P = .009) and HPA-3b (P = .004) alleles, and HPA-1a/1b (P = .045), HPA-1b/1b (P = .007), and HPA-3b/3b (P = .008) genotypes were higher in patients than control subjects. No significant association was demonstrated between the HPA variants and 1-, 2- and 3-vessel disease. HPA-1b/2a/3b (Pc = .021) and HPA-1b/2b/3a (Pc = .002) haplotypes were positively associated with CAD, thereby conferring a disease susceptibility nature to these haplotypes. Multivariate analysis confirmed the positive association of HPA-1b/2a/3b (aOR = 3.72; 95% CI = 1.49-9.28), and in addition identified HPA-1b/2a/3a (aOR = 2.49; 95% CI = 1.06-5.86) to be positively associated with CAD, after adjusting for a number of covariates. Our results demonstrate positive association of HPA variants and specific HPA-1/HPA-2/HPA-3 haplotypes with CAD in Tunisians.

The first case of alloantibody against human platelet antigen-15b in Japan: possible alloimmunization by a hydatidiform mole

BACKGROUND

The involvement of the human platelet antigen (HPA)-15 system in neonatal alloimmune thrombocytopenia (NAIT) has been reported in various populations, but not in the Japanese population. In Japan, the mixed passive hemagglutination assay (MPHA) is used for detection of HPA alloantibodies. However, most of the reported cases of HPA-15 incompatibility are based on the monoclonal antibody immobilization of platelet antigen (MAIPA) assay or immunoprecipitation; thus there is a possibility that HPA-15 alloantibodies are not efficiently detected by the MPHA, and currently, the causative antibody is not detectable in approximately half of the suspected NAIT cases in Japan.

STUDY DESIGN AND METHODS

We examined the sera of mothers from NAIT cases, previously with undetected HPA antibodies by MPHA, using the MAIPA technique. Sera from 90 mothers of suspected NAIT were tested by MAIPA for the presence of anti-HPA-15 alloantibodies.

RESULTS

Anti-HPA-15b was detected in one case. This case was a mother in the first pregnancy diagnosed as hydatid mole-coexisting fetus, and the baby was born with suspected NAIT. The familial analysis revealed compatibility of HPA-15 genotype between the mother and the baby (both HPA-15a/a), but incompatibility with the paternal one (HPA-15a/b). The hydatid mole's tissue was genotyped as HPA-15b positive. Besides anti-HPA-15b, maternal sera contain strong HLA Class I antibody

CONCLUSIONS

Here we reported the first case of anti-HPA-15 in Japan. Alloimmunization against the hydatid mole seems to be responsible for the production of HPA-15b alloantibody. This antibody, however, did not apparently involve in the development of NAIT of the newborn, the coexisting anti-HLA Class I being the possible cause.

Human platelet alloantigens (HPA) 1, HPA2, HPA3, HPA4, and HPA5 polymorphisms in sickle cell anemia patients with vaso-occlusive crisis

OBJECTIVES

Vaso-occlusive crisis (VOC) is a significant cause of morbidity and mortality in sickle cell anemia (SCA) patients. Insofar as polymorphism in human platelet alloantigen (HPA) exhibit a prothrombotic nature, we hypothesized that specific HPA polymorphic variants are associated with VOC. We investigated the distribution of HPA1, HPA2, HPA3, HPA4, and HPA5 alleles genotypes among VOC and non-VOC control SCA patients.

PATIENTS/METHODS

This was a case-control study. Study subjects comprised SCA patients with (VOC group; n = 127) or without (Steady-state group; n = 130) VOC events. HPA genotyping was done by PCR-SSP.

RESULTS

Significantly higher frequencies of HPA-2b, HPA-3b, and HPA-5b alleles, and marked enrichment of HPA-3b/3b, HPA-5a/5b, and HPA-5b/5b genotypes, were seen in VOC than in control SCA patients. Taking homozygous wild-type genotypes as reference, univariate analysis identified HPA-3a/3b, HPA-3b/3b, and HPA-5b/5b to be associated with VOC. Multivariate analysis confirmed the independent association of only HPA-3a/3b and HPA-3b/3b genotypes with VOC. HPA-3 genotypes were significantly correlated with VOC frequency, type, and medication, and requirement for hospitalization. While both HPA 3a/3b (P = 0.002; OR = 2.94; 95% CI = 1.49-5.77) and 3b/3b (P = 0.006; OR = 3.16; 95% CI = 1.40-7.17) genotypes were associated with need for hospitalization, only HPA-3b/3b was associated with VOC frequency, type (localized vs. generalized), and medication (narcotics vs. NSAIDs).

CONCLUSION

This confirms the association of HPA polymorphisms with SCA VOC, of which HPA-3 appears to be independent genetic risk factors for SCA VOC.

Polymorphisms of human platelet alloantigens HPA-1 and HPA-2 associated with severe coronary artery disease

OBJECTIVES

Insofar as platelet membrane glycoprotein (GP) polymorphisms were identified as potential risk factors for coronary artery disease (CAD), we investigated the contribution of human platelet antigen (HPA)-1 (GPIIb/IIIa) and HPA-2 (GPIb/IX) alleles and haplotypes to CAD pathogenesis.

METHODS

Study subjects comprised 247 middle-age CAD patients and 316 age-, gender-, and race-matched controls; HPA genotyping was performed by polymerase chain reaction with sequence specific primers.

RESULTS

The frequencies of HPA-1b (P<.001) and HPA-2b (P<.001) alleles and HPA-1a/1b (P<.001), HPA-1b/1b (P<.001), and HPA-2a/2b (P<.001) genotypes were higher in patients than control subjects. Select HPA haplotypes comprising the HPA-1b/2a (Pc=2.2 × 10(-4)) and HPA-1b/2b (Pc=.001) haplotypes which were positively associated, and the HPA-1a/2a (Pc=3.2 × 10(-5)) which was negatively associated with CAD, confer a disease susceptibility and protective nature to these haplotypes. Multivariate analysis confirmed the positive association of HPA-1b/2a [adjusted odds ratio (aOR)=3.63; 95% CI=2.42-5.43] and HPA-1b/2b (aOR=2.92; 95% CI=1.43-5.94) haplotypes with CAD, after adjustment for a number of covariates.

CONCLUSIONS

Our results suggest that HPA-1/HPA-2 haplotypes may be considered to be a major risk factor for CAD in middle-aged Tunisians.

Inherited prothrombotic risk factors in children with stroke, transient ischemic attack, or migraine

OBJECTIVE

The aim of this study was to investigate the prevalence and possible association of inherited prothrombotic risk factors in children with stroke, transient ischemic attack, or migraine.

METHODS

We performed genotypic analysis for factor V G1691A, factor II G20210A, methylenetetrahydrofolate reductase C677T, and 4 common platelet glycoprotein polymorphisms (human platelet alloantigen-1, -2, -3, and -5) in 150 children <18 years of age with established diagnoses of stroke, transient ischemic attack, or migraine. Children were classified into 5 groups, namely, childhood arterial ischemic stroke (N = 33), perinatal arterial ischemic stroke (N = 26), hemorrhagic stroke (N = 20), transient ischemic attack (N = 36), and migraine (N = 35). The control group consisted of 112 children < or =18 years of age from the same geographical region who had no history of neurologic or thromboembolic diseases.

RESULTS

Heterozygosity for factor V G1691A was associated with approximately sevenfold increased risk for arterial ischemic stroke, perinatal arterial ischemic stroke, and transient ischemic attack. Increased risk for transient ischemic attack was found in carriers of the human platelet alloantigen-2b allele, human platelet alloantigen-5a/b genotype, and combined human platelet alloantigen-2b and human platelet alloantigen-5b genotype. The presence of the human platelet alloantigen-2b allele was associated with a 2.23-fold increased risk for migraine, whereas carriers of the human platelet alloantigen-3b allele had a lower risk for arterial ischemic stroke than did carriers of the human platelet alloantigen-3a allele.

CONCLUSIONS

Factor V G1691A has an important role in susceptibility to arterial ischemic stroke, both in the perinatal/neonatal period and in childhood, as well as transient ischemic attacks. A minor impact of human platelet alloantigen polymorphisms suggests that platelet glycoprotein polymorphisms may increase the risk of transient ischemic attacks and migraine, but this should be confirmed in larger studies.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for genotyping of human platelet-specific antigens

BACKGROUND

Genotyping of single-nucleotide polymorphisms (SNPs) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an emerging technique, where finally tools for end users have become available to design primers and analyze SNPs of their own interest. This study investigated the potential of this technique in platelet (PLT) genotyping and developed a validated method for genotyping of clinical relevant human PLT antigens (HPAs).

STUDY DESIGN AND METHODS

A multiplex assay using MALDI-TOF MS to analyze six HPA loci (HPA-1, HPA-2, HPA-3, HPA-4, HPA-5, and HPA-15) simultaneously in a single reaction was applied for the genotyping of 100 DNA samples from a cohort of plateletpheresis donors and a patient population (n = 20) enriched for rare alleles. The genotyping results using MALDI-TOF MS were validated by the comparison with the results from typing by polymerase chain reaction with sequence-specific primers and conventional DNA sequencing.

RESULTS

Both homozygous and heterozygous genotypes of HPA-1 to -5 and -15 of the 120 individuals were easily identified by a six-plexed assay on MALDI-TOF MS. The three approaches achieved a 100 percent concordance for the genotyping results of the six HPA loci.

CONCLUSION

Compared to conventional methods, the MALDI-TOF MS showed several advantages, such as a high velocity, the ability to perform multiplexed assays in a single reaction, and automated high-throughput analysis of samples. This enables cost-efficient large-scale PLT genotyping for clinical applications.

Real-time PCR assays for high-throughput human platelet antigen typing

Most human platelet alloantigen (HPA) systems comprise biallelic single nucleotide polymorphisms in genes encoding major membrane glycoproteins. Genotyping for these systems is required in the investigation of patients with suspected HPA antibodies and for the provision of compatible blood products from HPA-typed donor panel populations.

Polymorphisms of the human platelet alloantigens HPA-1, HPA-2, HPA-3, and HPA-4 in ischemic stroke

Polymorphism in human platelet antigen (HPA)-1 and HPA-3 (GPIIb/IIIa), HPA-2 (GPIb/IX), HPA-4 (GPIIIa), and HPA-5 (GPIa/IIa) was investigated in 329 stroke patients and 444 matched control subjects. HPA genotyping was done by PCR-SSP method. Lower HPA-1a (P < 0.001) and higher HPA-1b (P < 0.001) allele frequencies were seen in patients than control subjects, and homozygosity for HPA-1b (P < 0.001) alleles was more prevalent in stroke cases than in controls. The allele and genotype distributions of the other HPA polymorphic variants were similar between cases and controls. Select HPA combined genotypes comprising the 2121 (Pc = 0.008) and 2221 (Pc = 0.018) genotypes, which were positively associated, and the 1111 (Pc < 0.001), which was negatively associated with stroke, thereby conferred a disease susceptibility and protective nature to these genotype combinations. Multivariate analysis confirmed the negative association of the 1111 (P < 0.001) and the positive association of the 2121 (P = 0.017) combined genotypes with stroke, after adjustment for a number of covariates. This is the first evidence demonstrating differential association of the common 4 HPA gene variants and specific HPA genotype combinations with stroke.

Human AB serum and thrombin-activated platelet-rich plasma are suitable alternatives to fetal calf serum for the expansion of mesenchymal stem cells from adipose tissue

MSCs are currently in focus regarding their clinical potential in cell therapy and tissue engineering. However, most isolation and expansion protocols for clinical-scale production of MSCs use fetal calf serum (FCS) as a supplement, which poses a potential risk for infections as well as immunological reactions. To find a suitable FCS substitute, we investigated the effects of pooled human AB serum (AB-HS) and thrombin-activated platelet-rich plasma (tPRP) on adipose tissue MSCs (AT-MSCs) with FCS as the standard control medium. AT-MSCs of 10 donors were cultured under three different conditions: (a) 10% FCS, (b) 10% AB-HS, and (c) 10% tPRP. Colony-forming units, cumulative population doubling rates, and differentiation capacity toward the adipogenic and osteogenic lineages were assessed, along with immunophenotype. We demonstrated that AB-HS and tPRP provide a significantly higher proliferative effect on AT-MSCs than does FCS. In the first six passages, AB-HS and tPRP MSCs exhibited a fold expansion of 66.6 +/- 15.7 and 68.1 +/- 6.7, respectively, compared with 24.4 +/- 0.7 for FCS. Differentiation capacity was preserved throughout long-term culture. Immunophenotype was characteristic for MSCs and comparable for all culture conditions with the exception of a distinct CD45-/CD14-positive side population for AB-HS and tPRP that tended to diminish with prolonged culture. We showed that pooled human AB serum and thrombin-activated platelet-rich plasma are alternatives to FCS for AT-MSCs. These human sources are better characterized regarding potential infectious threats, while providing a higher proliferation rate and retaining differentiation capacity and mesenchymal stem cell marker expression throughout long-term culture. Disclosure of potential conflicts of interest is found at the end of this article.

Fetoneonatal alloimmune thrombocytopenia (FNAIT): Our experience

OBJECTIVE

Fetoneonatal alloimmune thrombocytopenia (FNAIT) is a relatively rare clinical syndrome characterized by marked thrombocytopenia shortly after birth. It occurs when fetal platelets are destroyed, after sensitization, by a transplacental passage of maternal antibodies directed against a fetal platelet alloantigen inherited from the father. This article reviews some pathophysiologic and clinical aspects of FNAIT.

METHODS

We also present our experience with the management of 12 newborns affected with a symptomatic form of this disorder in order to verify what would be the best diagnostic and therapeutic protocols.

RESULTS

Antibody identification in maternal serum showed 9 anti-HPA-1a (75% of cases), 2 anti-HPA-1b (17%) and 1 anti-HPA-1a+anti-Gp IV+anti-HLA class I (8%).

CONCLUSION

Sixteen human platelet alloantigen (HPA) systems have been identified, six major (from HPA 1 to 5 and HPA 15) and ten rare or private, each composed of two allelic antigens (named "a" or "b", according to major or minor frequency in the population). All HPA systems, including private or low frequency, may play a role in determining FNAIT. Unfortunately FNAIT cannot be prevented, in fact no one of maternal parameters is predictive of thrombocytopenia or its magnitude.

Genotyping of human platelet antigens 1 to 6 and 15 by high-resolution amplicon melting and conventional hybridization probes

High-resolution melting techniques are a simple and cost-effective alternative to other closed-tube genotyping methods. Here, we genotyped human platelet antigens (HPAs) 1 to 6 and 15 by high-resolution melting methods that did not require labeled probes. Conventional melting analysis with hybridization probes (HybProbes) was also performed at each locus. HybProbe assays were performed individually, whereas amplicon melting (HPAs 1 to 5 and 16) and unlabeled probe (HPA 6) assays were duplexed when possible. At all loci for each method, both homozygous and heterozygous genotypes were easily identified. We analyzed 100 blinded clinical samples (33 amniotic fluid, 12 cultured amniocytes, and 55 blood samples) for all 7 single-nucleotide polymorphisms (SNPs) by each method. Genotype assignments could be made in 99.0% of the SNPs by high-resolution melting and in 98.7% of the SNPs with HybProbes with an overall genotype concordance of 98.8%. Errors included two sample misidentifications and six incorrect assignments that were all resolved by repeating the analysis. Advantages of high-resolution melting include rapid assay development and execution, no need for modified oligonucleotides, and similar accuracy in genotyping compared with other closed-tube melting methods.

Characterization of major histocompatibility complex-associated peptides from a small volume of whole blood

Class I major histocompatibility complex (MHC) presents intracellular-derived peptides on the majority of cells within the human body. Intracellular proteins are degraded into peptides of 8-11 amino acids, allowing them to fit into the groove of an empty MHC class I molecule. Detection of MHC-associated peptides can be challenging with the major difficulty being the ability to obtain peptides in adequate concentration. Published protocols require a large sample size that is unrealistic for a clinically available sample. Based on calculations, it should be possible to characterize MHC-associated peptides from cells obtained from 30 ml of whole blood. A citric acid wash of whole platelets was implemented to release the peptides with sample cleanup by reversed-phase high-performance liquid chromatography on a peptide trap. Peptides were analyzed by liquid chromatography tandem mass spectrometry. Four peptides were identified from an individual's platelets. The binding motifs of the peptides were consistent with the published MHC binding motif of the individual. Since red blood cells do not express MHC, they were used as a negative control. Using citric acid wash of whole cells and a peptide trap, the more abundant MHC-associated peptides can be identified. This report demonstrates the identification of peptides from a sample volume compatible with reasonable clinical availability.