When the available blood supply mismatches the needs of the patient.

BACKGROUND: Substantial regional differences in the genetic patterns related to blood group have been observed across different continents. This diversity means that the blood supply, as an essential part of patient care, is increasingly impacted by global migration. Consequently, the Austrian blood donor population does not match the immigrant patient population. This mismatch is likely to result in the formation of alloantibodies to red cell antigens in the chronically transfused. Subsequently, major difficulties in providing compatible blood emerge. MATERIAL AND METHODS: The study included patients of African origin (n=290) and Caucasians who represent the Austrian donor population (n=1,017). Genetic typing was performed for up to 69 blood group polymorphisms with a multiplex sequence specific primer-PCR including high frequency antigens and antigens for which antisera are not commercially available. By assessing differences in antigen frequencies between the two populations, and using these data for prophylactic matching, we aim to develop tools to increase the quality of patient care. RESULTS: Results indicate various and significant differences (p<0.0001) in antigen frequencies between African patients and the European donor population, especially in the MNS, Duffy, Knops and Rhesus systems. DISCUSSION: Our data highlight the importance of matching the donor population to the demographics of the patient population. In addition, it underlines the need to recruit donors of African origin and to focus on the upcoming challenges, such as malaria semi-immunity and a significantly higher rate of infectious disease in this population. It is also recommended to apply extended genetic typing to detect rare blood types, and (cryo)storage of rare blood in national and international rare blood banks. Co-operation with regional blood banks should also be encouraged.

Naturally occurring anti-PP1PK in a Chinese individual with p phenotype: A case based on compound heterozygosity including one novel allele.

BACKGROUND: The null phenotype in P1PK blood group, known as "p," is extremely rare in the whole world. Individuals of p phenotype spontaneously form anti-PP1PK isoantibody. Here, we report a case of p phenotype with naturally occurring anti-PP1PK isoantibodies in a Chinese individual. STUDY DESIGN AND METHODS: Serology tests, containing alloantibodies screening and identification, were conducted to demonstrate the phenotype in P1PK blood group. The genotype of A4GALT gene was identified by haplotypes separation and sequencing. RESULTS: The serological assay demonstrated the p phenotype of the proband, presenting with 1:64 titer of anti-PP1PK . The sequencing data revealed a compound heterozygote consisting of A4GALT*P1.01 with c.343A>T and a novel allele based on A4GALT*01N.05 with an addition polymorphism c.100G>A. The sequence of the novel allele has been submitted to GenBank and the accession number OM912503 was assigned. CONCLUSION: Our study demonstrates a case of naturally occurring anti-PP1Pk in a Chinese individual with p phenotype, which is based on compound heterozygosity including one novel allele. As the proband is a young lady, monitoring the titer of anti-PP1PK and early initiation of medical intervention are essential after her pregnancy.

Genetic Alterations, DNA Methylation, Alloantibodies and Phenotypic Heterogeneity in Type III von Willebrand Disease.

Type III von Willebrand disease is present in the Punjab province of Pakistan along with other inherited bleeding disorders like hemophilia. Cousin marriages are very common in Pakistan so genetic studies help to establish protocols for screening, especially at the antenatal level. Factors behind the phenotypic variation of the severity of bleeding in type III vWD are largely unknown. The study was conducted to determine Mutations/genetic alterations in type III von Willebrand disease and also to determine the association of different mutations, methylation status, ITGA2B/B3 mutations and alloimmunization with the severity of type III vWD. After informed consent and detailed history of the patients, routine tests and DNA extraction from blood, mutational analysis was performed by Next Generation Sequencing on Ion Torrent PGM. DNA methylation status was also checked with the help of PCR. In our cohort, 55 cases were detected with pathogenic mutations. A total of 27 different mutations were identified in 55 solved cases; 16 (59.2%) were novel. The mean bleeding score in truncating mutations and essential splice site mutations was relatively higher than weak and strong missense mutations. The mean bleeding score showed insignificant variation for different DNA methylation statuses of the VWF gene at the cg23551979 CpG site. Mutations in exons 7,10, 25, 28, 31, 43, and intron 41 splice site account for 75% of the mutations.

Hemophilia A gene therapy: current and next-generation approaches.

INTRODUCTION: Hemophilia comprises a group of X-linked hemorrhagic disorders that result from a deficiency of coagulation factors. The disorder affects mainly males and leads to chronic pain, joint deformity, reduced mobility, and increased mortality. Current therapies require frequent administration of replacement clotting factors, but the emergence of alloantibodies (inhibitors) diminishes their efficacy. New therapies are being developed to produce the deficient clotting factors and prevent the emergence of inhibitors. AREAS COVERED: This article provides an update on the characteristics and disease pathophysiology of hemophilia A, as well as current treatments, with a special focus on ongoing clinical trials related to gene replacement therapies. EXPERT OPINION: Gene replacement therapies provide safe, durable, and stable transgene expression while avoiding the challenges of clotting factor replacement therapies in patients with hemophilia. Improving the specificity of the viral construct and decreasing the therapeutic dose are critical toward minimizing cellular stress, induction of the unfolded protein response, and the resulting loss of protein production in liver cells. Next-generation gene therapies incorporating chimeric DNA sequences in the transgene can increase clotting factor synthesis and secretion, and advance the efficacy, safety, and durability of gene replacement therapy for hemophilia A as well as other blood clotting disorders.

Marginal zone B cells mediate a CD4 T-cell-dependent extrafollicular antibody response following RBC transfusion in mice.

Red blood cell (RBC) transfusions can result in alloimmunization toward RBC alloantigens that can increase the probability of complications following subsequent transfusion. An improved understanding of the immune mechanisms that underlie RBC alloimmunization is critical if future strategies capable of preventing or even reducing this process are to be realized. Using the HOD (hen egg lysozyme [HEL] and ovalbumin [OVA] fused with the human RBC antigen Duffy) model system, we aimed to identify initiating immune factors that may govern early anti-HOD alloantibody formation. Our findings demonstrate that HOD RBCs continuously localize to the marginal sinus following transfusion, where they colocalize with marginal zone (MZ) B cells. Depletion of MZ B cells inhibited immunoglobulin M (IgM) and IgG anti-HOD antibody formation, whereas CD4 T-cell depletion only prevented IgG anti-HOD antibody development. HOD-specific CD4 T cells displayed similar proliferation and activation following transfusion of HOD RBCs into wild-type or MZ B-cell-deficient recipients, suggesting that IgG formation is not dependent on MZ B-cell-mediated CD4 T-cell activation. Moreover, depletion of follicular B cells failed to substantially impact the anti-HOD antibody response, and no increase in antigen-specific germinal center B cells was detected following HOD RBC transfusion, suggesting that antibody formation is not dependent on the splenic follicle. Despite this, anti-HOD antibodies persisted for several months following HOD RBC transfusion. Overall, these data suggest that MZ B cells can initiate and then contribute to RBC alloantibody formation, highlighting a unique immune pathway that can be engaged following RBC transfusion.

Serologic and molecular studies to identify neonatal alloimmune neutropenia in a cohort of 10,000 neonates.

Neonatal alloimmune neutropenia (NAIN) is caused by maternal alloimmunisation to fetal human neutrophil antigens (HNAs). This study investigated maternal HNA/HLA alloantibodies involved with NAIN and identified the frequency of NAIN in Brazilian neonates. Neonatal neutropenia (neutrophil count < 1.5 × 109 /L) was investigated in samples from 10,000 unselected neonates, resulting in 88 neutropenic newborns (NBs) and their 83 mothers. Genotyping was performed by PCR-SSP (HNA-1/-4) and PCR-RFLP (HNA-3/-5). Serologic studies were performed by GAT (granulocyte agglutination test), Flow-WIFT (white blood cells immunofluorescence test) and LABScreen-Multi-HNA-Kit (OneLambda®) (LSM). Neonatal neutropenia was identified in 88/10,000 (0·9%) NBs. Genotyping revealed 60·2% maternal-fetal HNA incompatibilities (31·8% for HNA-1; 14·8% for HNA-3; 15·9% for HNA-4; 21·6% for HNA-5). Serologic studies revealed 37·3% of mothers with positive results with at least one technique. The detected anti-HNA specificities were confirmed in eight positive cases related to HNA-1/-3 systems. In cases with maternal-fetal HNA-4/-5 incompatibility, no specific neutrophil alloantibodies were found but anti-HLA I/II were present. Anti-HNA-2 was not identified. This is a large Brazilian study which involved the investigation of antibodies against all five HNA systems in neutropenia cases and showed a frequency of NAIN in 8/10,000 neonates. Among the HNA antibodies identified, we highlight the anti-HNA-1d and anti-HNA-3b, antibodies unusual in alloimmunised women, and rarely related to NAIN cases.

SCAR: The high-prevalence antigen 013.008 in the Scianna blood group system.

BACKGROUND: The Scianna (SC) blood group system comprises seven antigens. They reside on the erythroblast membrane-associated glycoprotein (ERMAP). The ERMAP and RHCE genes are juxtaposed to each other on chromosome 1. We report a novel SC antigen. STUDY DESIGN AND METHODS: Blood samples came from a patient and his two sisters in Saudi Arabia. To investigate the antibody specificity we used the column agglutination technique and soluble recombinant ERMAP protein. The significance of anti-SCAR was evaluated by the transfusion history and a monocyte monolayer assay. We determined the genomic sequence of ERMAP and RHCE genes. RESULTS: The patient's serum showed an antibody of titer 8 against a high-prevalence antigen. The soluble recombinant ERMAP protein inhibited the antibody. The propositus genotyped homozygous for an ERMAP:c.424C>G variant, for which his sisters were heterozygous. The c.424C>G variant occurred in the SC*01 allele in one haplotype with the RHCE*03 (RHCE*cE) allele. No signs of hemolysis occurred following an incompatible blood transfusion. The monocyte monolayer assay was negative. CONCLUSIONS: We characterized a high-prevalence antigen, with the proposed name "SCAR," which is the eighth antigen of the Scianna blood group system (proposed designation 013.008). Individuals homozygous for ERMAP:p.(Gln142Glu) protein variant can produce anti-SCAR. Although we did not observe any sign of hemolysis at this time, the anti-SCAR prompted a change of the treatment regimen. A review of the known reports indicated that all SC alloantibodies of sufficient titer should be considered capable of causing hemolysis.

Spectrum of F8 Genotype and Genetic Impact on Inhibitor Development in Patients with Hemophilia A from Multicenter Cohort Studies (J-HIS) in Japan.

Some genetic and treatment-related factors are risk factors for inhibitor development in patients with hemophilia A (PwHA). However, the genotype distribution of the factor VIII gene (F8) and genetic impact on inhibitor development in Japanese PwHA remain unknown. In 2007, the Japan Hemophilia Inhibitor Study 2 (J-HIS2) was organized to establish a nationwide registry system for hemophiliacs and to elucidate risk factors for inhibitor development, designed for prospective investigation following a retrospective study (J-HIS1) which had already finished. Patients, newly diagnosed after January 2007, were enrolled in J-HIS2 and followed up for inhibitor development and clinical environments since 2008 onward. In the present study, F8 genotypes of PwHA were investigated in the patients recruited from the J-HIS2 cohort as well as those with inhibitor from the J-HIS1 cohort. F8 variants identified in 59 PwHA with inhibitor in J-HIS1 were: 20 intron-22 inversions, 5 intron-1 inversions, 9 large deletions, 4 nonsense, 8 missense, 11 small in/del, and 2 splice-site variants. F8 variants identified in 267 (67 with inhibitor) PwHA in J-HIS2 were: 76(28) intron-22 inversions, 3(2) intron-1 inversion, 1(0) duplication, 8(5) large deletions, 21(7) nonsense, 109(7) missense, 40(11) small in/del, and 9(7) splice-site variants. Forty variants were novel. The cumulative inhibitor incidence rate in the severe group with null changes was 42.4% (95% confidence interval [CI]: 33.7-50.8), higher than that with nonnull changes (15.6% [95%CI: 6.8-27.8]), in J-HIS2. Relative risk for inhibitor development of null changes was 2.89. The spectrum of F8 genotype and genetic impact on inhibitor development in Japanese PwHA were consistent with the previous reports.

Type 1 Interferon Gene Signature Promotes RBC Alloimmunization in a Lupus Mouse Model.

Red blood cell (RBC) transfusion exposes recipients to hundreds of unmatched minor RBC antigens. This exposure can lead to production of alloantibodies that promote clinically significant hemolytic events. Multiple studies have reported an increased frequency of RBC alloimmunization in patients with autoimmunity. However, cellular and molecular mechanisms that underlie autoimmunity-induced alloimmunization have not been reported. Patients with systemic lupus erythematosus (SLE) have a high frequency of alloimmunization and express a type 1 interferon (IFNα/ß) gene signature. Thus, we utilized the pristane-induced lupus mouse model to test the hypothesis that inflammation in lupus promotes RBC alloimmunization, and to examine the potential role of IFNα/ß. Intraperitoneal injection of pristane, a hydrocarbon oil, led to autoantibody production, glomerulonephritis, and pulmonary hemorrhage in wild type (WT) mice. Pristane treatment significantly induced serum IFNα and expression of multiple interferon-stimulated genes (ISGs) in peripheral blood and peritoneal fluid cells, including inflammatory macrophages. Following transfusion with allogeneic RBCs expressing the KEL glycoprotein, pristane-treated WT mice produced significantly elevated levels of anti-KEL IgM and anti-KEL IgG, compared to untreated mice. Pristane induced comparable levels of inflammatory cells and cytokines in mice lacking the IFNα/ß receptor (IFNAR1-/-) or the IFNα/ß-inducing transcriptions factors (IRF3/7-/-), compared to WT mice. However, pristane-treated IFNAR1-/- and IRF3/7-/- mice failed to produce ISGs and produced significantly lower levels of transfusion-induced anti-KEL IgG, compared to WT mice. Thus, pristane induction of a lupus-like phenotype promoted alloimmunization to the KEL RBC antigen in an IFNα/ß-dependent manner. To our knowledge, this is the first examination of molecular mechanisms contributing to RBC alloimmunization in a model of autoimmunity. These results warrant further investigation of the role of IFNα/ß in alloimmunization to other RBC antigens and the contribution of the IFNα/ß gene signature to the elevated frequency of alloimmunization in patients with SLE.

Simultaneous fluorescence imaging of distinct nerve and blood vessel patterns in dual Thy1-YFP and Flt1-DsRed transgenic mice.

Blood vessels and nerve tissues are critical to the development and functionality of many vital organs. However, little is currently known about their interdependency during development and after injury. In this study, dual fluorescence transgenic reporter mice were utilized to observe blood vessels and nervous tissues in organs postnatally. Thy1-YFP and Flt1-DsRed (TYFD) mice were interbred to achieve dual fluorescence in the offspring, with Thy1-YFP yellow fluorescence expressed primarily in nerves, and Flt1-DsRed fluorescence expressed selectively in blood vessels. Using this dual fluorescent mouse strain, we were able to visualize the networks of nervous and vascular tissue simultaneously in various organ systems both in the physiological state and after injury. Using ex vivo high-resolution imaging in this dual fluorescent strain, we characterized the organizational patterns of both nervous and vascular systems in a diverse set of organs and tissues. In the cornea, we also observed the dynamic patterns of nerve and blood vessel networks following epithelial debridement injury. These findings highlight the versatility of this dual fluorescent strain for characterizing the relationship between nerve and blood vessel growth and organization.

Genetic testing to resolve the source of haemolytic antibody in solid organ transplantation.

BACKGROUND: Antibody-mediated haemolysis due to passenger lymphocyte syndrome arising in the setting of solid organ transplant can be devastating. Some degree of passenger lymphocyte syndrome is said to occur in up to 10% of ABO mismatched renal transplants, 40% of ABO mismatched liver transplants, and 70% of ABO mismatched heart-lung transplants; a reflection of the number of memory B cells transplanted with the organ. Passenger lymphocyte syndrome is less common with minor red cell antigens but can still be severe. MATERIALS AND METHODS: We review a series of patients who developed passenger lymphocyte syndrome after solid organ transplantation. Conventional serological testing was performed using tube and solid-phase testing. Molecular testing was performed using a gene-chip array. RESULTS: In patients receiving a minor antigen mismatched organ transplant and multiple allogenic red cell transfusions, serological methods proved insufficient to resolve the source of minor blood group antibodies that arose in the aftermath of the transplant. Genetic testing was able to clearly resolve donor and recipient types. DISCUSSION: Passenger lymphocyte syndrome after mismatched organ transplantation is not rare, but the syndrome associated with non-ABO antibodies occurs in a much smaller subset of these cases. The mixtures of organ donor, recipient, and other transfused red blood cells profoundly limit the usefulness of serological testing. Genetic assignment of minor blood types to donor and recipient can guide therapy and inform prognosis.

Defining the structural basis for human alloantibody binding to human leukocyte antigen allele HLA-A*11:01.

Our understanding of the conformational and electrostatic determinants that underlie targeting of human leukocyte antigens (HLA) by anti-HLA alloantibodies is principally based upon in silico modelling. Here we provide a biochemical/biophysical and functional characterization of a human monoclonal alloantibody specific for a common HLA type, HLA-A*11:01. We present a 2.4 Å resolution map of the binding interface of this antibody on HLA-A*11:01 and compare the structural determinants with those utilized by T-cell receptor (TCR), killer-cell immunoglobulin-like receptor (KIR) and CD8 on the same molecule. These data provide a mechanistic insight into the paratope-epitope relationship between an alloantibody and its target HLA molecule in a biological context where other immune receptors are concomitantly engaged. This has important implications for our interpretation of serologic binding patterns of anti-HLA antibodies in sensitized individuals and thus, for the biology of human alloresponses.

The Biology of IgG Subclasses and Their Clinical Relevance to Transplantation.

Immunoglobulin G (IgG) is the dominant immunoglobulin and can be divided into 4 distinct subclasses. The evolution of IgG subclass switches is regulated by interaction with T cells and follows a 1-way direction (IgG3 → IgG1 → IgG2 → IgG4). Based on their structure, the 4 IgG subclasses can initiate different effector function such as complement activation, recruitment of various cells by Fc receptors, and agonistic signaling. Using current assays for HLA antibody detection as a template and replacing the generic reporter antibody with IgG subclass-specific reporter antibodies, it is possible to investigate the IgG subclasses of HLA antibodies. There are 15 different IgG subclass compositions possible. Based on the capability to activate the complement system and the class switch direction, 3 arbitrary patterns can be defined (ie, only complement-binding subclasses [IgG3 and/or IgG1], expansion to noncomplement-binding subclasses [IgG3 and/or IgG1 plus IgG2 and/or IgG4], and switch to noncomplement-binding subclasses [IgG2 and/or IgG4]). The latter group accounts for less than 5%, whereas the former 2 groups have a similar prevalence close to 50%. In the past 5 years, several studies correlated the IgG subclass pattern with occurrence of antibody-mediated rejection and allograft outcomes. Because of differences of the used IgG subclass assay, the time point of analyses, and the definition of outcomes, a clear picture has not emerged yet. Future needs are standardization of the assay, a more detailed knowledge of the initiated effector functions, and more well-designed clinical studies also looking at changes of the IgG subclass pattern over time.

Alloantibodies in von Willebrand Disease.

von Willebrand disease (VWD), the most commonly known inherited bleeding disorder, is caused by a partial (type 1) or total (type 3) deficiency or dysfunction (type 2) of von Willebrand factor (VWF). Its management encompasses the prevention or treatment of bleeding by raising endogenous VWF levels using a synthetic agent, such as desmopressin, or providing exogenous VWF concentrates. The development of inhibitory alloantibodies against VWF is a rare but often severe complication encountered during the treatment of type 3 VWD, which is associated with a lack of hemostatic response to infused VWF concentrates and more rarely with allergic, even anaphylactic, reactions. This narrative review will focus on the characteristics of such alloantibodies and their management, which can be very challenging for physicians operating at hemophilia treatment centers.

Defining the phenotype of antibody-mediated rejection in kidney transplantation: Advances in diagnosis of antibody injury.

The diagnostic criteria for antibody-mediated rejection (ABMR) are constantly evolving in light of the evidence. Inclusion of C4d-negative ABMR has been one of the major advances in the Banff Classification in recent years. Currently Banff 2015 classification requires evidence of donor specific antibodies (DSA), interaction between DSA and the endothelium, and acute tissue injury (in the form of microvasculature injury (MVI); acute thrombotic microangiopathy; or acute tubular injury in the absence of other apparent cause). In this article we review not only the ABMR phenotypes acknowledged in the most recent Banff classification, but also the phenotypes related to novel pathogenic antibodies (non-HLA DSA, antibody isoforms and subclasses, complement-binding functionality) and molecular diagnostic tools (gene transcripts, metabolites, small proteins, cytokines, and donor-derived cell-free DNA). These novel tools are also being considered for the prognosis and monitoring of treatment response. We propose that improved classification of ABMR based on underlying pathogenic mechanisms and outcomes will be an important step in identifying patient-centered therapies to extend graft survival.

Epitopes and motifs of the HLA-B*14 allele family products and related HLA-B14 cross-reactive specificities.

The split specificities of HLA-B14 (B64, B65) are assigned to the B*14:01 (B64) and B*14:02 (B65) products only. Of the further 50 B*14 expressed products, only B*14:03 and B*14:06 are officially designated as HLA-B14. The B*14:08 product differs from B64 by a single amino acid substitution of W97R, while the B*14:53 specificity (which is a "short" B14 and neither B64 nor B65) differs from B64 by three residues (W97S, Y113H and F116Y). Comprehensive testing of B*14:08:01 cells (using 49 alloantisera with B64 or B64, B65 specificities, and five monoclonal antibodies with B65 or B64, B65 activity) showed that the B*14:08 specificity is, like the B*14:53 product, neither B64 nor B65 and appears as a "short" B14 specificity. To help understand the serological reactivity of the B*14:08 and B*14:53 products, and B64 and B65, we identified seven published epitopes (11AV, 97W, 61ICT, 116F, 131S+163T, 170RH and 420) and, by inspection, 29 motifs, that encompass one or more of B64, B65 and various HLA-B14 cross-reactive group specificities. We then considered the possession of these epitopes and motifs by the products of B*14:01 to B*14:06, B*14:08 and B*14:53. Seventeen of the 29 motifs fully complied with the one-/two-patch functional epitope concept for amino acid proximity, as determined by Cn3D software, the remainder partially complied. The nature and patterns of epitopes and motifs possessed by both B*14:08 and B*14:53 specificities supported their designation as HLA-B14 but non-B64/B65. Also that epitope 97W, with 11S or 11A, is critical for serological B64 and B65 reactivity. And conversely, that epitope 116F, and several identified motifs, are probably unimportant for HLA-B14 antibody reactivity. The previous submission that the B*14:03 specificity is HLA-B65 was compatible with its epitope/motif pattern. B*14:04 cells would also be expected to react as B65, based on its epitope/motif pattern, and not as B64 as previously implied. Also, from their epitope/motif patterns, and external serological information, it is probable that the B*14:05 and B*14:06 specificities will both appear as "short" HLA-B14, non-B64/B65. Several epitopes and motifs encompassed a range of HLA-B specificities included in the serological HLA-B14 cross-reactive group, thus supporting these original serological findings.

An HLA-B7-specific antibody in an HLA-B*07 positive patient explained by a nonexpressed allele (HLA-B*07:181N).

Antibody identification by a bead array assay in a kidney patient revealed several HLA-specific antibodies including one directed against the HLA-B7 antigen. Low-resolution typing of the patient indicated the presence of an HLA-B*07 allele. To rule out an HLA-specific autoantibody the HLA-typing of the patient was further refined by nucleotide sequencing on a next-generation sequencing platform and eventually showed an HLA-B*39:01:01:03 and HLA-B*07:181N genotype. Thereby the allospecific nature of the antibody was proven. The HLA-B7-specific antibody could be explained by an immunization during the first kidney-transplantation in 1996 with an HLA-B*07 positive donor. When assessing the plausibility of antibodies, the presence of nonexpressed alleles should be taken into consideration.

Genetic background of the rare Yus and Gerbich blood group phenotypes: homologous regions of the GYPC gene contribute to deletion alleles.

The GYPC gene encodes the glycophorins C and D. The two moieties express 12 known antigens of the Gerbich blood group system and functionally stabilize red blood cell membranes through their intracellular interaction with protein 4.1 and p55. Three GYPC exon deletions are responsible for the lack of the high-frequency antigens Ge2 (Yus type, exon 2 deletion), Ge2 and Ge3 (Gerbich type, exon 3 deletion), and Ge2 to 4 (Leach type, exons 3 and 4 deletion), but lack exact molecular description. A total of 29 rare blood samples with Yus (GE:-2,3,4) and Gerbich (GE:-2,-3,4) phenotypes, including individuals of Middle-Eastern, North-African or Balkan ancestry were examined genetically. All phenotypes could be explained by 4 different Yus alleles, characterized by deletions of exon 2 and adjacent introns, and 3 different Gerbich alleles, with deletions of exon 3 and adjacent introns. A 3600 base pair GYPC region, encompassing exon 2 and flanking region, shares a high degree of sequence homology with a region flanking exon 3, probably representing an evolutionary duplication event. Defining the expression of Gerbich variants presently relies on rare serological reagents. Our approach substitutes the serological characterization with a precise genotype approach to identify the rare Yus and Gerbich alleles.

CRISPR/Cas9-mediated conversion of human platelet alloantigen allotypes.

Human platelet alloantigens (HPAs) reside on functionally important platelet membrane glycoproteins and are caused by single nucleotide polymorphisms in the genes that encode them. Antibodies that form against HPAs are responsible for several clinically important alloimmune bleeding disorders, including fetal and neonatal alloimmune thrombocytopenia and posttransfusion purpura. The HPA-1a/HPA-1b alloantigen system, also known as the Pl(A1)/Pl(A2) polymorphism, is the most frequently implicated HPA among whites, and a single Leu33Pro amino acid polymorphism within the integrin ß3 subunit is responsible for generating the HPA-1a/HPA-1b alloantigenic epitopes. HPA-1b/b platelets, like those bearing other low-frequency platelet-specific alloantigens, are relatively rare in the population and difficult to obtain for purposes of transfusion therapy and diagnostic testing. We used CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9) gene-editing technology to transform Leu33 (+) megakaryocytelike DAMI cells and induced pluripotent stem cells (iPSCs) to the Pro33 allotype. CD41(+) megakaryocyte progenitors derived from these cells expressed the HPA-1b (Pl(A2)) alloantigenic epitope, as reported by diagnostic NciI restriction enzyme digestion, DNA sequencing, and western blot analysis using HPA-1b-specific human maternal alloantisera. Application of CRISPR/Cas9 technology to genetically edit this and other clinically-important HPAs holds great potential for production of designer platelets for diagnostic, investigative, and, ultimately, therapeutic use.