Anti-human platelet antigen-1a alloantibody (Anti-HPA-1a)

Anti-HPA-1a alloantibodies are pathogenic IgG molecules produced by HPA-1a-negative individuals (typically HPA-1b/1b) following exposure to the HPA-1a antigen, which is a leucine-33 polymorphism on the integrin beta-3 (GPIIIa) subunit of the platelet glycoprotein IIb/IIIa complex (Newman et al., 1989, J Clin Invest). These antibodies are the primary cause of fetal and neonatal alloimmune thrombocytopenia (FNAIT), a condition where maternal antibodies cross the placenta and opsonize fetal platelets, leading to their destruction by the fetal reticuloendothelial system (Peterson et al., 2013, Blood Reviews). This immune-mediated destruction can result in severe fetal thrombocytopenia and life-threatening intracranial hemorrhage (Ghevaert et al., 2015, Blood). In adults, these antibodies are also the causative agent in post-transfusion purpura (PTP), a rare but severe bleeding disorder following blood component transfusion. Therapeutic strategies targeting these alloantibodies include the use of neonatal Fc receptor (FcRn) inhibitors, such as nipocalimab, which accelerate the clearance of pathogenic IgG from maternal circulation and reduce placental transfer (Ling et al., 2022, Clin Pharmacol Ther). Additionally, prophylactic monoclonal antibodies like RLYB212 are being developed to prevent maternal sensitization by masking the HPA-1a antigen or clearing HPA-1a-positive cells before an immune response is initiated (Rallybio, 2023).

Other names

Anti-HPA-1aAnti-Zw(a)Anti-Pl(A1)Human platelet antigen 1a antibodyAnti-integrin beta-3 alloantibody

Neonatal Fc receptor (FcRn) antagonism to reduce maternal IgG levels and placental transfer; Antibody-mediated immune suppression (AMIS) for prophylaxis; Passive immunization with hyperimmune globulin.