In vivo and in vitro activity of an immunoglobulin Fc fragment (Fcab) with engineered Her-2/neu binding sites.

Antigen-binding Fc fragments (Fcabs) are a new unique class of immunotherapeutics. They are small (50 kD) fully functional antibody alternatives that bind antigen and elicit effector functions such as antibody-dependent cytotoxicity (ADCC) and complement-dependent cytotoxicity. Since Fcabs carry the natural FcRn binding site of antibodies, they have very favorable pharmacokinetics.