Red blood cell (RBC) transfusions are a crucial component in the treatment of a number of acute and chronic medical problems. In most acute injuries, simple RBC typing (ABO/Rh) is sufficient to identify appropriate donors. However, problems are frequently encountered in individuals, usually minorities, receiving chronic transfusions (e.g., sickle cell anemia and the thalassemias). Indeed, simple blood typing often becomes insufficient in determining a proper match as these individuals develop transfusion reactions to minor RBC antigens. This reactivity to minor RBC antigens can make it nearly impossible to identify appropriate blood donors. Thus, it would be desirable to artificially disguise cellular antigenic determinants to permit the survival of heterologous donor RBC and prevent allosensitization from occurring. To date this has not been possible. However, previous studies have demonstrated that the covalent linkage of poly(ethylene glycol) [PEG] to proteins both prolongs in vivo circulation and also prevents/diminishes protein antigenicity. Similarly, studies on liposomes have demonstrate that inclusion of PEG-conjugated lipids in the membrane also prolonged in vivo circulation. Based on these findings, it is the hypothesis of this proposal that the covalent binding of non-immunogenic, long chain polymers (e.g., PEG or PEG derivatives) to intact RBC can effectively mask the antigenic determinants on donor RBC, reduce RBC immunogenicity, and diminish/prevent transfusion reactions arising from disparity between donor and recipient RBC phenotypes. Therefore, the Specific Aims of this proposal are to determine: 1) which compounds effectively mask RBC antigenicity and examine how molecular weight and geometric shape (linear vs. branched) of PEG/PEG-derivatives affect cellular immunogenicity; 2) the structural, functional and metabolic consequences of RBC derivatization with PEG/PEG-derivatives; and 3) the effects of RBC-derivatization on in vitro and in vivo survival. As outlined within the proposal, preliminary studies using this technology demonstrates that derivatized human RBC are morphologically normal and exhibit significantly decreased: ABO/minor RBC antigenicity, immunogenicity, binding of anti-RBC antibodies and phagocytosis. Furthermore, derivatized mouse RBC exhibit normal in vivo survival. In sum, the covalent attachment of non-immunogenic materials to intact RBC may have significant clinical applications. These include, but are not limited to, derivatization of human RBC to permit transfusions in patients difficult to match, allosensitized to minor RBC antigens, and possibly in individuals with severe autoimmune hemolytic disease.
