Mechanisms and prevention of alloimmunization in pregnancy

Transfusion only occasionally gives rise to antibody production, because blood cells per se are not markedly immunogenic. However, the immunological changes that occur during pregnancy increase the risk of alloimmunization against red blood cells, platelets, and/or leukocytes. Fetal-maternal bleeding during pregnancy or in relation to delivery is the antigenic stimuli for immunization against red blood cells, whereas other mechanisms, such as trophoblast-derived microparticles, may also play a role in the production of antibodies against platelets. Antibody-mediated immune suppression has for 4 decades successfully been used for prevention of RhD immunization. Result from a mouse model of fetal and neonatal alloimmune thrombocytopenia (FNAIT) suggests that the same principle may be applied for the prevention of FNAIT. A European Union-funded consortium is presently in the process of developing a hyperimmune anti-human platelet antigen 1a (HPA-1a) immunoglobulin G. The idea is to prevent HPA-1a immunization by administering the drug to nonimmunized HPA-1a-negative women after delivery of an HPA-1a-positive child. The anti-HPA-1a will be purified from plasma collected from women who previously have given birth to a child with FNAIT caused by anti-HPA-1a. If the results of the planned phase III trial are favorable, it is possible that a product for prevention of FNAIT will be available within this decade.