Proteomic study of apheresis platelets made HLA class I deficient for transfusion of refractory patients

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.

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.

Effects of storage on quality and function of acid-treated platelets with reduced HLA Class I surface expression

BACKGROUND

Refractory patients need to be provided with HLA-matched platelets (PLTs), which require time-consuming cross-matching. Treatment of PLTs with citric acid leads to denaturation of the HLA Class I complexes without significant damage to the PLTs. HLA Class I depleted PLTs could alternatively be used to HLA-matched PLTs for transfusion. These PLTs have verified normal function up to 4-6 h after acid treatment.

MATERIALS AND METHODS

Buffy coat (BC) PLT concentrates were depleted of HLA Class I complexes by incubation in citric acid. The days after acid-treatment, surface expression of HLA Class I complexes, CD62P and CD63 were determined by flow cytometry, in addition to viability and mitochondrial membrane potential (MMP). Thromboelastography (TEG) tested PLT functionality.

RESULTS

Expression of HLA Class I complexes was reduced by 70%-75% in acid-treated PLTs compared to untreated PLTs from day 1 through day 7. Controls and acid-treated PLTs showed insignificant loss of MMP stored for 4 days. Analysis of the residual PLT activation and viability showed no significant differences for 4 days of storage. However, the residual PLT activation potential and viability were significantly decreased in acid-treated PLTs and control PLTs after 7 days of storage. Acid treatment caused a significant decrease in the TEG variable, reaction time (R time), for acid-treated PLTs as compared to control PLTs from days 1 through day 3.

CONCLUSION

Our data suggest that extended storage of acid-treated PLTs is possible and will improve flexibility when planning for transfusion of patients with alloimmune PLT refractoriness caused by anti-HLA-antibodies.

Anti-HLA Class I alloantibodies in platelet transfusion refractoriness: From mechanisms and determinants to therapeutic prospects

Patients with hematological disorders and severe thrombocytopenia require extensive and iterative platelet transfusion support. In these patients, platelet transfusion refractoriness represents a serious adverse transfusion event with major outcomes for patient care. Recipient alloantibodies against the donor HLA Class I antigens expressed at the cell surface of platelets result in a rapid removal of transfused platelets from the circulation and thus, therapeutic and prophylactic transfusion failure leading to a major bleeding risk. In this case, the only way to support the patient relies on the selection of HLA Class I compatible platelets, an approach restricted by the limited number of HLA-typed donors available and the difficulty of meeting the demand in an emergency. However, not all patients with anti-HLA Class I antibodies develop refractoriness to platelet transfusions, raising the question of the intrinsic characteristics of the antibodies and the immune-mediated mechanisms of platelet clearance associated with a refractory state. In this review, we examine the current challenges in platelet transfusion refractoriness and detail the key features of the antibodies involved that should be considered. Finally, we also provide an overview of future therapeutic strategies.