C1-Inhibitor Rescues Red Blood Cells From Complement Mediated Destruction in Autoimmune Hemolytic Anemia

Abstract 716

In autoimmune hemolytic anemia (AIHA) autoantibodies (auto-Ab's) to red blood cells (RBCs) may induce complement activation via the classical pathway of complement resulting in complement deposition on RBCs. RBCs coated with auto-Ab and/or complement (C3b) are removed by extravascular destruction in the spleen and liver. In a minority of cases complement activation proceeds until insertion of the membrane attack complex (MAC) resulting in intravascular hemolysis. The inflammatory response and the anoxia induced by hemolysis significantly contribute to the morbidity and fatality in AIHA. However, the recovery of RBC transfusion in these situations is inadequate since auto-Abs to RBC also react with donor cells leading to rapid destruction of RBC. Activation of classical pathway of complement is critically involved in this process. C1-inhibitor (Cetor) is a plasma-derived inhibitor of the classical pathway of complement with an excellent safety profile. We hypothesized that co-administration of C1-inhibitor concentrate with a RBC transfusion improves recovery of a transfusion by attenuation of the activation of the classical pathway of complement. In order to test this hypothesis we adapted a standard haemolytic assay (CH50). Sera from patients (n=6) with AIHA due to IgM antibodies with reactivity above 30°C induced dose-dependent lysis of bromealin-treated RBC, whereas sera from healthy donors (n=4) did not. Addition of C1-inhibitor concentrate dose-dependently inhibited RBC lysis significantly in this model. Subsequently, by flowcytometry we studied C3 deposition on RBC after incubation with AIHA patient sera or sera from healthy controls. Anti-C5 antibody (eculizumab) was added in order to prevent lysis during analysis. AIHA sera containing eculizumab induced extensive C3 deposition on RBC, which was significantly inhibited by C1-inhibitor concentrate. This inhibition was dose-dependent. Next, we were interested whether these in-vitro effects could also be observed in-vivo. A 65 year old patient suffering from fulminant life threatening hemolysis due to IgM type auto-Abs reactive >30°C was admitted to our department. Despite treatment with anti-CD20, vincristine and high-dose methylprednisolone the anaemia did not improve necessitating transfusion of 3 RBC concentrates. However, 2.5 day after transfusion the starting haemoglobin levels was reached again and hemolysis deteriorated. Since the patient became symptomatic again the next transfusion of 3 RBC concentrates was preceded by infusion of 6000 U of C1-inhibitor. Three additional donations of 4000 U, 2000 U and 1000 U of C1-inhibitor concentrate have been administered 12, 24 and 36 hours after the first dose, respectively. The recovery of the transfusion significantly increased and was accompanied by a decrease in C3 deposition on RBC, as evidenced by an attenuation of the direct antiglobulin test. In conclusion we have demonstrated that in-vitro C1-inhibitor concentrate can efficiently inhibit RBC lysis and C3 deposition on RBC induced by sera from patients with AIHA. Moreover we have shown that this approach is also effecitive in-vivo. Therefore, in AIHA administration of C1-inhibitor concentrate might be life-saving by improving recovery of RBC transfusion by inhibition of both intra- and extravascular destruction of recipient and donor RBCs.