A humanized immunotoxin directed against the Lewis Y antigen conjugated with calicheamicin, a hydrophobic enediyne antibiotic, with potential antineoplastic activity. CMD193 binds to the Lewis Y antigen, a tetrasaccharide expressed on the cell surfaces of many tumor cell types. Upon binding, CMD-193 is internalized, thereby delivering the attached calicheamicin to Lewis Y antigen-expressing tumor cells. Calicheamicin binds non-covalently to the minor groove of DNA and prompts conformational changes and DNA oxidation, thereby inhibiting DNA synthesis and inducing apoptosis.