Recombinant humanized IgG4, kappa antibody conjugated with a cytotoxic antitumor antibiotic, calicheamicin, isolated from fermentation of a bacterium, Micromonospora echinospora ssp. calichensis. The antibody portion of Mylotarg binds specifically to the CD33 antigen, The anti-CD33 hP67.6 antibody is produced by mammalian cell suspension culture using a myeloma NS0 cell line. Gemtuzumab ozogamicin (trade name Mylotarg) was withdrawn in 2010 when a clinical trial showed the drug increased patient death and exhibited no advantages over traditional cancer therapies.