Anchoring IgG-degrading enzymes to the surface of platelets selectively neutralizes antiplatelet antibodies

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.

Imlifidase Desensitization in HLA-incompatible Kidney Transplantation: Finding the Sweet Spot

Imlifidase, derived from a Streptococcus pyogenes enzyme, cleaves the entire immunoglobulin G pool within hours after administration in fully cleaved antigen-binding and crystallizable fragments. These cleaved fragments can no longer exert their antibody-dependent cytotoxic functions, thereby creating a window to permit HLA-incompatible kidney transplantation. Imlifidase is labeled, in Europe only, for deceased donor kidney transplantation in highly sensitized patients, whose chances for an HLA-compatible transplant are negligible. This review discusses outcomes of preclinical and clinical studies on imlifidase and describes the phase III desensitization trials that are currently enrolling patients. A comparison is made with other desensitization methods. The review discusses the immunological work-up of imlifidase candidates and especially the "delisting strategy" of antigens that shift from unacceptable to acceptable with imlifidase desensitization. Other considerations for clinical implementation, such as adaptation of induction protocols, are also discussed. Imlifidase cleaves most of the currently used induction agents except for horse antithymocyte globulin, and rebound of donor-specific antibodies should be managed. Another consideration is the timing and interpretation of (virtual) crossmatches when bringing this novel desensitization agent into the clinic.

Expression and prognostic value of C-reactive protein in adult immune thrombocytopenia (ITP) patients

The aim of this study was to investigate the effect of C-reactive protein (CRP) on the prognosis of adult patients with Immune thrombocytopenia purpura (ITP). A retrospective study of 628 adult ITP patients, as well as 100 healthy and 100 infected patients, attending the Affiliated Hospital of Xuzhou Medical University from January 2017 to June 2022 was performed. The ITP patients were grouped according to their CRP levels, and the differences in clinical characteristics of each group and the influencing factors of efficacy in newly diagnosed ITP patients were analyzed. CRP levels were significantly higher in the ITP and infected groups compared with healthy controls (P < 0.001), and platelet counts were significantly lower in the ITP group (P < 0.001). Between the CRP normal and elevated group, their age, white blood cell count, neutrophil count, lymphocyte count, red blood cell count, hemoglobin, platelet count, complement C3 and C4, PAIgG, bleeding score, proportion of severe ITP, and proportion of refractory ITP were significantly different (P < 0.05). Patients of severe ITP (P < 0.001), refractory ITP (P = 0.002), and with active bleeding (P < 0.001) had significantly higher CRP levels. Patients with no response after treatment had significantly higher CRP levels than those who achieved CR or R (P < 0.001). Platelet counts (r = - 0.261, P < 0.001) in newly diagnosed ITP patients and treatment outcomes (r = - 0.221, P < 0.001) were negatively correlated with CRP levels, and bleeding score was positively correlated with CRP levels (r = 0.207, P < 0.001). Treatment outcome was positively correlated with decrease in CRP levels (r = 0.313, P = 0.027). A multifactorial regression analysis of the influencing factors of treatment outcomes on newly diagnosed patients found that CRP was an independent risk factor of the prognosis (P = 0.011). In conclusion, CRP can help assess the severity and predict the prognosis of ITP patients.

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.

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.