Characterization of complement receptor 1 domains for prevention of complement-mediated red cell destruction

Complement activation resulting in intravascular hemolysis can cause transfusion-associated mortality. We recently showed that a recombinant soluble form of complement receptor 1 (CR1) effectively reduces complement-mediated red blood cell (RBC) destruction in vitro and more importantly prolongs the survival of transfused human RBCs in mice. To determine CR1-active sites that prevent RBC destruction, structure-function analysis of its extracellular 1930-amino-acid domain has been performed.

Several CR1-truncated soluble proteins were prepared and tested for their ability to prevent complement-mediated RBC destruction in vitro and in mice.

A 250-amino-acid region in CR1 that possesses antihemolytic activity and is effective in prolonging survival of transfused RBCs in vivo was identified. Mutation of two critical residues (D109N and E116K) in this 250-amino-acid domain, previously shown to improve complement-inhibitory functions of CR1 derivatives, resulted in a more potent inhibition of complement activation in vitro. In vivo, however, the activity of mutant proteins was comparable to the wild-type molecules.

Our structure-function studies have characterized smaller CR1-based complement inhibitors for future development of structure-derived transfusion therapeutics. Our studies underscore the importance of testing CR1 inhibitors in vivo.