The ability to conjugate an antibody to another protein or molecule is critically important for many applications in life science research, diagnostics, and therapeutics. Antibody conju- gates have become one of the most important classes of biological agents associated with tar- geted therapy for cancer and other diseases. There literally are dozens of markers that have been identified on tumor cells to which monoclonal antibodies have been developed for tar- geted therapy (Carter et al., 2004). The preparation of antibody conjugates to find and destroy cancer cells in vivo has become one of the leading strategies of research into investigational new drugs (McCarron et al., 2005). In most cases, the site-specific delivery of drugs involves the successful development of defined monoclonal antibody conjugates that can target diseased cells without affecting normal ones.