Clinical determinants of red cell alloimmunizatiom, implications for preventative antigen matching strategies

Transfusion of red blood cells (RBCs) causes exposure to foreign antigens and, consequently, may induce alloimmunization. This research focused on identifying clinical determinants of RBC alloimmunization, eventually aiming to prevent alloimmunization by pre-emptively select extended matched blood for the predicted responder patient. Both RBC antigen intrinsic characteristics and patient-related factors were studied. Regarding antigen immunogenicity, K was confirmed to be the most potent antigen, followed by E, Cw, e, Jka and c. Of importance, anti-Jka is known to easily induce complement-mediated hemolysis. Inflammation due to severe bacterial and viral infections was associated to increased RBC alloimmunization incidences. Remarkably, although in line with murine models, Gram-negative bacteremia coincided with a twofold reduction of alloimmunization risk. In a non-hemoglobinopathy population, alloimmunization post-splenectomy was a highly unlikely event. Consequently, the Caucasian splenectomized patient does not benefit from RBC products matched beyond ABO/RhD. Patients with acute (either myeloid of lymphoblastic) leukemia, mature lymphomas, myelodysplastic syndrome, or patients post-autologous or -allogeneic stem cell transplantation demonstrated strongly reduced incidences of RBC alloimmunization, primarily explained by the intense immunosuppressive nature of treatments. Consequently, matching for the MDS population deserves renewed focus and should be based on the cumulative transfusion burden rather than on the diagnosis itself.