Efalizumab is an immunosuppressive recombinant humanized IgG1 monocolonal antibody (150 Kd) that binds to human CD11a (1) and is used for the treatment of plaque psoriasis. Efalizumab was derived from the humanization of the murine efalizuman monoclonal antibody MHM24, which recognizes human and chimpanzee CD11a. Humanization of MHM24 was accomplished by grafting the murine complementarity determining regions (hypervariable region) into consensus human IgG1/ heavy and light chain sequences (Werther et al 1996). These same consensus human immunoglobulin sequences have been successfully used in the humanization of other murine antibodies, including those targeted to HER2 and IgE. Efalizumab inhibits the binding of LFA-1 to intercellular adhesion molecule-1 (ICAM-1) thereby inhibiting the adhesion of leukocytes to other cell types.