Interactions of IgM ABO antibodies and complement with methoxy-PEG-modified human RBCs

BACKGROUND: RBCs modified with cyanuric chloride activated methoxy-PEG (CmP EG; 5000 Da) are less immunogenic than untreated RBCs, and their use thus m ay reduce the risk of alloimmunization in chronically transfused patients. STUDY DESIGN AND METHODS: To further examine the potential utility of CmPEG -RBCs, the effects of derivatization on an arm of the immune system that pl ays an important role in transfusion rejection-the complement system-were d etermined. RESULTS: When CmPEG-RBCswere incubated in autologous or heterologous ABO-ma tched serum, no classical or alternative pathway consumption was found, no C3a was generated, no cell-bound C3b or C9 was detected, and no cell lysis occurred. Cell-bound complement regulation was normal for CmPEG-RBCs, as de termined by acidified serum or reactive lysis assays. CmPEG-RBCs differed f rom control RBCs only when incubated in ABO-mismatched serum. In that case, CmPEG modification failed to protect against ABO antibody-dependent comple ment-mediated lysis. Indeed, cell lysis was actually enhanced at CmPEG conc entrations >1.0 mM. CONCLUSION: The enhanced lysis of CmPEG-RBCs in ABO-mismatched serum correl ated with increased IgM binding and C3a generation and elevated C3b and C9 membrane deposition. While PEG modification effectively blocks non-ABO anti gens, these data show that ABO matching is still required. Once ABO-matched , these modified RBCs retain great potential for the prevention of alloimmu nization.