An epitope-based approach of HLA-matched platelets for transfusion: a noninferiority crossover randomized trial

Immunological platelet transfusion refractoriness: current insights from mechanisms to therapeutics

Although there have been tremendous improvements in the production and storage of platelets, platelet transfusion refractoriness (PTR) remains a serious clinical issue that may lead to various severe adverse events. The burden of supplying platelets is worsened by rising market demand and limited donor pools of compatible platelets. Antibodies against platelet antigens are known to activate platelets through FcγR-dependent or complement-activated channels, thereby rapidly eliminating foreign platelets. Recently, other mechanisms of platelet clearance have been reported. The current treatment strategy for PTR is to select appropriate and compatible platelets; however, this necessitates a sizable donor pool and technical assistance for costly testing. Consolidation of these mechanisms should be of critical significance in providing insight to establish novel therapeutics to target immunological platelet refractoriness. Therefore, the purposes of this review were to explore the modulation of the immune system over the activation and elimination of allogeneic platelets and to summarize the development of alternative approaches for treating and avoiding alloimmunization to human leukocyte antigen or human platelet antigen in PTR.

Transfusion-induced HLA sensitization in wait-list patients and kidney transplant recipients

Human leukocyte antigen (HLA) sensitization remains an impediment to successful solid organ transplantation, whether it be chances of receiving a transplant offer or subsequent transplant longevity. Current treatments targeting HLA antibodies lack long-term effectiveness; therefore, preventing HLA sensitization should remain a priority in all potential wait-list candidates and transplant recipients. Recent advances in the management of anemia in patients with chronic kidney disease may reduce the need for red cell transfusions. However, data from several anemia intervention studies of novel therapeutic agents have shown that a need for transfusion will remain. It has also been increasingly recognized that blood transfusions following kidney transplantation, especially in the peri-operative period, are common. Routine data on transfusion incidence, indications, and outcomes are not captured by most kidney and transplant registries across the globe. This restricts the evidence to inform both clinicians and patients on the clinical effects of transfusion, which have been considered both an allogeneic stimulus and to be immunomodulatory.This review aims to provide an update on what is currently known about transfusion-induced HLA sensitization in wait-list candidates and transplant recipients, summarizes where evidence is lacking, and demonstrates the distinct need for patient blood management guidelines in the field of kidney transplantation.

Establishment and Application of a Multiplex PCR NGS Method for the Genotyping of HLA-Class I and HPA

Selecting compatible HLA-Class I and/or HPA platelets based on genotyping could alleviate immune platelet transfusion refractoriness (PTR). A fast and reliable method of HLA-Class I and HPA genotyping is necessary to construct a platelet donor bank with known HLA-Class I and HPA genotypes. Ten pairs of specific primers for HLA-A, HLA-B, HLA-C, HPA-1 through HPA-6w, HPA-15 and HPA-21w were designed. The appropriate fragments were optimised for amplification in a single multiplex reaction. After a cleanup step using paramagnetic beads, the amplicon library was prepared and sequenced. To validate the accuracy of the developed method, commercial NGS kits for the genotyping of HLA-A, HLA-B and HLA-C and the TaqMan real-time PCR method in-house for the genotyping of HPA-1 through HPA-6w, HPA-15 and HPA-21w were used to detect all the specimens in parallel. A total of 386 specimens were detected and the results of genotyping HLA-A, HLA-B, HLA-C and HPA-1 through HPA-6w, HPA-15 and HPA-21w were obtained simultaneously, which is 100% consistent between the two methods. Four new HLA alleles, HLA-A*11:451, HLA-A*30:01:26, HLA-B*39:201 and HLA-B*40:538, were also reconfirmed. Two novel SNVs, c.2671C > T and c.2681T > G, in the coding region of ITGA2B were detected, all of which are heterozygous in individuals. A novel NGS method based on multiplex PCR was established to detect HLA-Class I and HPA simultaneously, which is high-throughput, rapid and accurate and could be applied to build a platelet donor bank.

Cumulative donor-specific antibody threshold predicts platelet transfusion response in HLA-alloimmunized patients

ABSTRACT

Up to a third of patients with hemato-oncologic conditions who have received multiply transfusions develop immune-mediated platelet transfusion refractoriness. Yet factors that influence posttransfusion platelet corrected count increments (CCI) in patients with HLA-alloimmune platelet transfusion refractoriness remain less well elucidated. Recent advances in HLA antibody characterization using fluorescent bead-based platforms enable the study of donor-specific antibody (DSA) avidity (as measured by mean fluorescence intensity [MFI]) and its impact on HLA-alloimmune platelet transfusion refractoriness. In this large retrospective study of 2012 platelet transfusions among 73 HLA-alloimmunized patients, we evaluated the impact of cumulative HLA DSA-MFI alongside other donor, platelet component, and patient characteristics on CCI at 2 and 24 hours after transfusion. As part of a quality improvement initiative, we also developed and tested a computerized algorithm to optimize donor-recipient histocompatibility based on cumulative DSA-MFI and sought other actionable predictors of CCI. In multivariate analyses, cumulative HLA DSA-MFI of ≥10 000, major/bidirectional ABO-mismatch, splenomegaly, transfusion reactions, and platelet storage in additive solution negatively affected 2-hour but not 24-hour posttransfusion CCI. The DSA-MFI threshold of 10 000 was corroborated by greater antibody-mediated complement activation and significantly more CCI failures above this threshold, suggesting the usefulness of this value to inform "permissive platelet mismatching" and to optimize CCI. Furthermore, DSA-MFI decreases were deemed feasible by the computer-based algorithm for HLA-platelet selection in a pilot cohort of 8 patients (122 transfusions) evaluated before and after algorithm implementation. When HLA-selected platelets are unavailable, ABO-identical/minor-mismatched platelet concentrates may enhance 2-hour CCI in heavily HLA-alloimmunized patients with platelet transfusion refractoriness.

Platelets retain function and can be stored following disruption of human leucocyte antigens

BACKGROUND AND OBJECTIVES

Antibodies to human leucocyte antigen (HLA) Class-I antigens can lead to refractoriness to platelet transfusion. Although this can be overcome by transfusion of HLA-compatible platelets, they are not always available. Disruption of HLA antigens on platelets by acid treatment may be a suitable alternative when no other components are available. The aim of this study was to assess the effect of HLA disruption and subsequent storage of platelet components.

MATERIALS AND METHODS

Platelet components were treated with 0.9% saline or citric acid solution (pH 3.0), and then stored until expiry (Day 7). HLA and platelet glycoprotein expression, platelet viability, activation and sialylation were measured by flow cytometry. Release of soluble factors was measured by ELISA and metabolism by biochemistry analyser. Reactivity to patient anti-sera containing anti-HLA antibodies was measured using platelet immunofluorescence tests (PIFTs) and monoclonal antibody immobilization of platelet antigen (MAIPA) assays. Platelet function was measured using aggregometry and thromboelastography (TEG).

RESULTS

Acid treatment reduced detection of HLA Class-I on platelets by 75%, with significant reductions in reactivity to patient anti-sera. Acid treatment reduced platelet content and viability, increased platelet activation and accelerated metabolism. Glycan cleavage was increased by acid treatment. Treatment reduced platelet activation following agonist stimulation by ADP and TRAP-6, but platelets remained functional, displaying increased aggregation response and reduced time to clot formation by TEG.

CONCLUSION

Although HLA disruption had some detrimental effects, acid-treated platelets remained functional, retaining their capacity to respond to agonists and form clots, and with further development could be used to support refractory patients.

Establishment and clinical application of the HLA genotype database of platelet-apheresis donors in Suzhou

The establishment of a platelet-apheresis donor database may provide a feasible solution to improve the efficacy of platelet transfusion in patients with immune platelet transfusion refractoriness (PTR). This study aimed to establish HLA genotype database in Suzhou, to provide HLA-I compatible platelets for PTR patients to ensure the safety and effectiveness of platelet transfusions. We used a polymerase chain reaction sequence-based typing (PCR-SBT) method to establish the database by performing high-resolution HLA-A, -B, and -C genotyping on 900 platelet-apheresis donors. HLA-I antibody was detected in patients using a Luminex device, and HLA-I gene matching was performed by an HLA-Matchmaker. We found that the highest frequency of the HLA-A allele was A*11:01 (17.06 %), followed by A*24:02 (14.67 %) and A*02:01 (13.61 %). The highest frequency of the HLA-B allele was B*46:01 (9.78 %), followed by B*40:01 (8.39 %) and B*13:02 (33 %). After the detection of platelet antibodies in 74 patients with immune PTR, we found 30 HLA-A antibodies and 48 HLA-B antibodies, and there were a variety of high frequency antibodies whose alleles were low in the donor database, such as HLA-A*68:02, and B*57:01. After avoiding donor-specific antibodies (DSA) matching, 102 of 209 platelet-compatible transfusions were effective, resulting in an effective rate of 48.8 %, which significantly improved the efficacy of platelet transfusion. The establishment of a platelet donor database is of great significance to improve the therapeutic effect of platelet transfusion in patients with hematologic disorder, and save blood resources, and it is also the premise and guarantee of precise platelet transfusion.

Platelet transfusions in haploidentical haematopoietic stem cell allograft candidates: Protecting HLA-A and HLA-B antigens through eplet analysis

In patients awaiting an allogeneic haematopoietic stem cell transplantation, platelet transfusion is a risk factor for anti-HLA class I immunization because the resulting donor-specific antibodies complicate the allograft process. The objective of the present study was to determine the feasibility of a novel eplet-based strategy for identifying HLA class I mismatches between potential donors and the recipient when pre-allograft platelet transfusions were required. We included 114 recipient/haploidentical relative pairs. For each pair, we entered HLA-class I typing data into the HLA Eplet Mismatch calculator, defined the list of mismatched eplets (for the recipient versus donor direction) and thus identified the shared HLAs to be avoided. Using this list of HLAs, we defined the theoretical availability of platelet components (PCs) by calculating the virtual panel-reactive antibody (vPRA). We also determined the number of PCs actually available in France by querying the regional transfusion centre's database. The mean ± standard deviation number of highly/moderately exposed eplets to be avoided in platelet transfusions was 5.8 ± 3.3, which led to the prohibition of 38.5 ± 2 HLAs-A and -B. Taking into account the mismatched antigens and the eplet load, the mean ± standard deviation theoretical availability of PCs (according to the vPRA) was respectively 34.49% ± 1.95% for HLA-A and 80% ± 2.3% for HLA-B. A vPRA value below 94.9% for highly or moderately exposed eplets would predict that 10 PCs were actually available nationally. Although epitope protection of HLA molecules is feasible, it significantly restricts the choice of PCs.

Guidelines for the diagnosis and management of adult aplastic anaemia: A British Society for Haematology Guideline

Pancytopenia with hypocellular bone marrow is the hallmark of aplastic anaemia (AA) and the diagnosis is confirmed after careful evaluation, following exclusion of alternate diagnosis including hypoplastic myelodysplastic syndromes. Emerging use of molecular cyto-genomics is helpful in delineating immune mediated AA from inherited bone marrow failures (IBMF). Camitta criteria is used to assess disease severity, which along with age and availability of human leucocyte antigen compatible donor are determinants for therapeutic decisions. Supportive care with blood and platelet transfusion support, along with anti-microbial prophylaxis and prompt management of opportunistic infections remain key throughout the disease course. The standard first-line treatment for newly diagnosed acquired severe/very severe AA patients is horse anti-thymocyte globulin and ciclosporin-based immunosuppressive therapy (IST) with eltrombopag or allogeneic haemopoietic stem cell transplant (HSCT) from a matched sibling donor. Unrelated donor HSCT in adults should be considered after lack of response to IST, and up front for young adults with severe infections and a readily available matched unrelated donor. Management of IBMF, AA in pregnancy and in elderly require special attention. In view of the rarity of AA and complexity of management, appropriate discussion in multidisciplinary meetings and involvement of expert centres is strongly recommended to improve patient outcomes.

Virtual platelet cross-matching as transfusion management for patients with immune platelet refractoriness

BACKGROUND AND OBJECTIVES

This study describes the use of the Epvix platform for virtual cross-matching (VC) of human leucocyte antigen (HLA)-compatible platelets for patients with immune platelet refractoriness, and demonstrates effectiveness of the selected platelets.

MATERIALS AND METHODS

A prospective cohort of haematological patients was evaluated from 2018 to 2022. HLA-typed donor bank profile was previously uploaded to the Epvix platform. Each patient's antibody reactivity panel (PRA) was included in the platform. Then, search, selection and VC were performed, and 24-h-corrected count increment (CCI) platelet transfusion was calculated (reference ≥2500).

RESULTS

Six patients were included (four female, two male), with mean age of 61 years. HLA antibodies were detected as the cause of immunity for all patients, whereas four patients also had non-immune causes. High percentage of alloimmunization was detected in all studied patients (mean PRA: 85.7%). Thirty different donors were able to schedule and perform platelet donations. The mean 24-h CCI count was 9882. All platelet transfusions achieved a satisfactory CCI count except for two transfusion events. Presence of non-immune causes identified in these two cases could account for the unsatisfactory CCI.

CONCLUSION

Epvix is a free application hosted on the Web and uses the HLAMatchmaker algorithm to generate histocompatibility reports. This study demonstrates the efficiency of VC performed by Epvix. However, physical cross-matching will still be necessary in some instances, as the platform does not support human platelet antigen polymorphism.

Platelet transfusion refractoriness due to HLA alloimmunization: Evolving paradigms in mechanisms and management

Platelet transfusion refractoriness due to HLA alloimmunization presents a significant medical problem, particularly among multiply transfused patients with hematologic malignancies and those undergoing hematopoietic stem cell transplants. HLA compatible platelet transfusions also impose significant financial burden on these patients. Recently, several novel mechanisms have been described in the development of HLA alloimmunization and platelet transfusion refractoriness. We review the history of platelet transfusions and mechanisms of HLA-sensitization and transfusion refractoriness. We also summarize advances in the diagnosis and treatment of platelet transfusion refractoriness due to HLA alloimmunization.

Development of a calculated panel reactive antibody calculator for the United Arab Emirates: a proof of concept study

Calculated panel reactive antibody (CPRA) is used to help increase sensitized patient's access to transplantation. United Arab Emirates (UAE) has a diverse resident population hence we developed a UAE-CPRA calculator based on HLA antigen frequencies of the different ethnic groups that represent the UAE population. HLA antigen frequencies at serological split antigen level for HLA-A, -B, -C, -DRB1 and -DQB1 of 1002 healthy unrelated donors were performed. We subsequently compared the performance of the UAE CPRA calculator with the Organ Procurement and Transplantation Network (OPTN) and the Canadian CPRA calculators in 110 Kidney Transplant waitlist patients from January 2016 to December 2018. Lin's concordance correlation coefficient showed a moderate agreement between the UAE and OPTN calculator (Rc = 0.949, 95% CI 0.929-0.963) and the UAE and Canadian calculators (Rc = 0.952, 95% CI 0.932-0.965). While there continued to be a moderate agreement (Rc = 0.937, UAE versus OPTN calculator) in the lower sensitized group, a poor agreement (Rc = 0.555, UAE versus OPTN calculator) was observed in the higher sensitized group. In this study, we provide a template for countries to develop their own population-specific CPRA calculator. Implementation of the CPRA algorithm based on HLA frequencies of the multi-ethnic UAE population will be more fitting to increase access to transplantation and improve transplant outcomes. Our study demonstrates that the CPRA calculators developed using the data from the western population had poor correlation in our higher sensitized patients disadvantaging them in potential organ allocations systems. We plan to further refine this calculator by using high resolution HLA typing to address the problem of a genetically diverse population.

Platelet transfusion in adults: An update

Many patients worldwide receive platelet components (PCs) through the transfusion of diverse types of blood components. PC transfusions are essential for the treatment of central thrombocytopenia of diverse causes, and such treatment is beneficial in patients at risk of severe bleeding. PC transfusions account for almost 10% of all the blood components supplied by blood services, but they are associated with about 3.25 times as many severe reactions (attributable to transfusion) than red blood cell transfusions after stringent in-process leukoreduction to less than 10⁶ residual cells per blood component. PCs are not homogeneous, due to the considerable differences between donors. Furthermore, the modes of PC collection and preparation, the safety precautions taken to limit either the most common (allergic-type reactions and febrile non-hemolytic reactions) or the most severe (bacterial contamination, pulmonary lesions) adverse reactions, and storage and conservation methods can all result in so-called PC "storage lesions". Some storage lesions affect PC quality, with implications for patient outcome. Good transfusion practices should result in higher levels of platelet recovery and efficacy, and lower complication rates. These practices include a matching of tissue ABH antigens whenever possible, and of platelet HLA (and, to a lesser extent, HPA) antigens in immunization situations. This review provides an overview of all the available information relating to platelet transfusion, from donor and donation to bedside transfusion, and considers the impact of the measures applied to increase transfusion efficacy while improving safety and preventing transfusion inefficacy and refractoriness. It also considers alternatives to platelet component (PC) transfusion.

Related donor platelet transfusion improves platelet transfusion refractoriness in hematological patients

Objective

Transfusion of HLA-matched platelets can reduce the effect of alloimmune responses on platelet transfusion efficacy; however, finding HLA-matched platelets in the population is nearly impossible. Almost all HLA-matched platelets from related are half-matched, but the hemostatic efficacy of related donor platelets is unclear. Our goal was to compare the hemostatic effect of related donated platelets and unrelated donors platelets.

Methods

In this retrospective cohort study, we included acute leukemia and myelodysplastic syndrome patients with thrombocytopenia after chemotherapy. These patients were all transfused with platelets. This study excluded patients younger than 16 years and older than 65 years, or patients with abnormal coagulation parameters during platelet transfusion. We compared the hemostatic effect of related donated platelets and unrelated donors platelet. The primary outcome was transfusion efficacy after platelet transfusion, and the number of platelet counts and corrected count increments at 24 h after platelet transfusion.

Result

We analyzed 31 patients who received platelet transfusions from related donors (Treatment group) and 35 patients who received platelet transfusions from unrelated donors (Comparator group). Except for the relatively small proportion of patients with myelodysplastic syndrome in the treatment group, baseline clinical and laboratory characteristics were similar between the two groups. Hemostasis and prevention of bleeding in the treatment group showed significant superiority; the number of platelets increased 24 h after platelet transfusion in the treatment group was significantly higher than that in the comparator group. After 24 h, the corrected count increments treatment group was also higher than the comparator group; in the treatment group, the transfusion effect was better when the three sites of HLA-A, B, and C were identical, and the different blood types of platelet donors and recipients did not affect the transfusion effect.

Conclusion

Related donated platelets have better hemostasis and prevention effects, and no increase in adverse blood transfusion reactions. It may be a better transfusion strategy for platelet refractoriness patients in emergency situations.

Altered Fc glycosylation of anti-HLA alloantibodies in hemato-oncological patients receiving platelet transfusions

BACKGROUND

The formation of alloantibodies directed against class I human leukocyte antigens (HLA) continues to be a clinically challenging complication after platelet transfusions, which can lead to platelet refractoriness (PR) and occurs in approximately 5%-15% of patients with chronic platelet support. Interestingly, anti-HLA IgG levels in alloimmunized patients do not seem to predict PR, suggesting functional or qualitative differences among anti-HLA IgG. The binding of these alloantibodies to donor platelets can result in rapid clearance after transfusion, presumably via FcγR-mediated phagocytosis and/or complement activation, which both are affected by the IgG-Fc glycosylation.

OBJECTIVES

To characterize the Fc glycosylation profile of anti-HLA class I antibodies formed after platelet transfusion and to investigate its effect on clinical outcome.

PATIENTS/METHODS

We screened and captured anti-HLA class I antibodies (anti-HLA A2, anti-HLA A24, and anti-HLA B7) developed after platelet transfusions in hemato-oncology patients, who were included in the PREPAReS Trial. Using liquid chromatography-mass spectrometry, we analyzed the glycosylation profiles of total and anti-HLA IgG1 developed over time. Subsequently, the glycosylation data was linked to the patients' clinical information and posttransfusion increments.

RESULTS

The glycosylation profile of anti-HLA antibodies was highly variable between patients. In general, Fc galactosylation and sialylation levels were elevated compared to total plasma IgG, which correlated negatively with the platelet count increment. Furthermore, high levels of afucosylation were observed for two patients.

CONCLUSIONS

These differences in composition of anti-HLA Fc-glycosylation profiles could potentially explain the variation in clinical severity between patients.

Association of Protective HLA-A With HLA-B∗27 Positive Ankylosing Spondylitis

Objectives

To further elucidate the role of the MHC in ankylosing spondylitis by typing 17 genes, searching for HLA-B^∗27 independent associations and assessing the impact of sex on this male biased disease.

Methods

High-confidence two-field resolution genotyping was performed on 310 cases and 2196 controls using an n-1 concordance method. Protein-coding variants were called from next-generation sequencing reads using up to four software programs and the consensus result recorded. Logistic regression tests were applied to the dataset as a whole, and also in stratified sets based on sex or HLA-B^∗27 status. The amino acids driving association were also examined.

Results

Twenty-five HLA protein-coding variants were significantly associated to disease in the population. Three novel protective associations were found in a HLA-B^∗27 positive population, HLA-A^∗24:02 (OR = 0.4, CI = 0.2–0.7), and HLA-A amino acids Leu95 and Gln156. We identified a key set of seven loci that were common to both sexes, and robust to change in sample size. Stratifying by sex uncovered three novel risk variants restricted to the female population (HLA-DQA1^∗04.01, -DQB1^∗04:02, -DRB1^∗08:01; OR = 2.4–3.1). We also uncovered a set of neutral variants in the female population, which in turn conferred strong effects in the male set, highlighting how population composition can lead to the masking of true associations.

Conclusion

Population stratification allowed for a nuanced investigation into the tightly linked MHC region, revealing novel HLA-B^∗27 signals as well as replicating previous HLA-B^∗27 dependent results. This dissection of signals may help to elucidate sex biased disease predisposition and clinical progression.