Inhibition of hyperacute transplant rejection by soluble proteins with thefunctional domains of CD46 and Fc gamma RII

Background. Recombinant soluble forms of complement regulatory molecules, i ncluding the human complement regulatory protein CD46 (rsCD46), have been s hown to inhibit hyperacute transplant rejection (HAR) and protect against c omplement- mediated inflammatory tissue damage. Similarly, recombinant solu ble forms of the immunoglobulin receptor Fc gamma RII (rsFc gamma RII) can attenuate antibody-mediated inflammatory responses. We have produced and te sted the function of novel recombinant chimeric proteins that, incorporate the functional domains of both CD46 (membrane cofactor protein, MCP) and th e low affinity human IgG receptor Fc gamma RII (CD32). Methods. Two recombinant soluble chimeric proteins (CD46:FcR and FcR:CD46) were designed and produced using a human cell expression system. Their abil ity to protect cells against complement-mediated lysis (through the CD46 do main) and bind human IgG (through the Fc receptor domain) was assessed in v itro. They were also tested in vivo in the rat reverse passive Arthus react ion and a murine model of hyperacute cardiac transplant rejection. Results. In vitro, the functional domains of the chimeric proteins each ret ained their activity. In vivo, the serum half-life of the recombinant chime ric proteins in mice was more than either rsCD46 or rsFc gamma RII, In the rat reverse passive Arthus reaction, intradermal injection of each recombin ant protein substantially reduced inflammatory skin edema (>50%) and polymo rphonuclear neutrophil infiltration (>90%). In the hyperacute rejection mod el, i.v. treatment with FcR:CD46 prevented complement-mediated rejection, m acroscopic bruising, edema, and thrombosis more effectively than rsCD46. Conclusions. CD46/Fc gamma RII bifunctional proteins have an improved abili ty to control complement-mediated hyperacute graft rejection and have thera peutic potential in other conditions involving antibody-mediated inflammati on.