Because of the observed significant preclinical activity in AML and CMML, clinical activity in chemorefractory patients with AML, the association of toxicities with steroid exposure, and association of the drug level with antibody titer that could be decreased with DT388GMCSF exposure, the current follow up phase I trial is designed based on a new administration and is a dose - finding trial also aimed to better determine and control side effects, improve drug pharmacokinetics and provide initial insight into antileukemic activity of this novel agent, delivered at a prolonged intermittent schedule.