Seattle Genetics, Inc. (Nasdaq:SGEN) announced today that it has initiated a phase I clinical trial of SGN-33, a humanized anti-CD33 monoclonal antibody, for patients with acute myeloid leukemia (AML) or myelodysplastic syndromes (MDS). The study is designed to evaluate the safety, pharmacokinetic profile and antitumor activity of escalating doses of SGN-33.