Molecular determinants of anti-RBC alloantibody evanescence

总结。对于需要长期输血的患者，红细胞抗体的产生

Summary. For patients who require chronic transfusion, the generation of antibodies to red blood cell (RBC) antigens can be a major clinical problem. Anti-RBC antibodies often make finding compatible blood difficult for these patients, which is particularly unfortunate since these RBC transfusions are often lifesaving. A major complication arises when these anti-RBC alloantibodies disappear before detection in the blood bank, a process referred to as evanescence. Patients whose antibodies have disappeared can unknowingly receive a second transfusion of incompatible blood. This incompatible transfusion can induce a life-threatening event called delayed hemolytic transfusion reaction. Anti-RBC evanescence therefore directly leads to delayed hemolytic transfusion reactions, which are a major cause of injury and death in chronically transfused patients. This is a particularly serious problem for patients with sickle cell disease, who often require frequent transfusions and have high rates of evanescent antibodies. Despite its clinical importance, the molecular factors that lead to anti-RBC alloantibody evanescence are completely unknown. Accordingly, there are no effective therapeutic interventions available to alloimmunized patients other than antigen avoidance. We have recently made the novel finding that the HOD mouse model of red blood cell (RBC) alloimmunization recapitulates many of the key clinical features seen in chronically transfused patients. Specifically, we have shown that HOD RBC transfusion leads to the preferential generation of low-affinity, rapidly evanescent anti- RBC alloantibodies at the expense of high-affinity, persistent antibodies. Herein we propose to use this mouse model to investigate why RBC transfusion leads to rapidly evanescent antibodies rather than long-lived ones. Our central hypothesis is that RBC presentation of antigens directly alters the innate immune responses of recipients, driving the differentiation of CD4+ T cells into helper cells which are unable to sustain long-lived interactions with B cells. We hypothesize that though these T cells can drive extrafollicular antibody responses that produce low-affinity, short-lived antibodies, they are blocked in their ability to drive germinal center responses that allow for somatic hypermutation, antibody affinity maturation, and long-lived antibody producing plasma cells. By better understanding how the fundamental cellular and molecular immune regulators of anti-RBC alloantibodies are regulated over time, we hope to discover novel molecular targets that can serve as potential future therapeutics for those patients who are at high risk from the complications of RBC alloimmunization.