The present invention provides recombinant peptides that specifically and selectively bind to the human milk fat globule (HMFG) antigen, BA46. In particular, the present invention provides recombinant variants of the Mc3 antibody, including humanized versions of Mc3. The variant Mc3 peptides are particularly useful for diagnostic, prognostic, and therapeutic applications in the field of breast cancer.The present invention also provides methods for the humanization of antibodies such as murine monoclonal antibodies. The novel humanization methods are applied to the production of humanized Mc3 antibodies and it is shown that these humanized antibodies retain the ability to engage in high affinity binding to their cognate antigen. Such humanization enables the use of these antibodies for immunodiagnostic and immunotherapeutic applications in humans.