Monoclonal antibodies for the treatment of acute myeloid leukemia

Currently, patients with acute myeloid leukemia (AML) are treated with cytotoxic chemotherapy and hematopoietic stem cell transplantation (HSCT). With this approach, the majority of patients still die of their disease because of both treatment-related mortality and relapse. Recently, monoclonal antibodies and immunoconjugates have been developed which potentially may increase the efficacy of treatment and decrease morbidity and mortality by specifically targeting the malignant cell. Unconjugated monoclonal antibodies have shown only moderate activity. A second, more effective, approach involves antibody conjugation with radioactive particles or chemotherapeutic agents, such as, immunotoxins, targeted delivery of cell killing. The antigens CD33, CD45, and CD66, are three antigens to which monoclonal antibodies have been directed. Most experience has been with gemtuzumab ozogamicin (Mylotarg) which is an immunoconjugate of an anti-CD33 antibody chemically linked to a potent cytotoxic agent, calicheamicin. Gemtuzumab ozogamicin appears to be particularly active in patients with acute promyelocytic leukemia, possibly related to the high expression of the CD33 antigen on the cell surface. Although gemtuzumab ozogamicin has activity as a single agent, the most promising result may be seen when this agent is combined with conventional cytotoxic chemotherapy. Preliminary studies have suggested a high complete remission rate and randomized clinical trials are underway. A unique potential toxicity has been identified, namely venoocclusive disease or sinusoidal obstructive syndrome which may be problematic among patients who subsequently undergo HSCT. An additional strategy includes radiolabeled monoclonal antibodies to intensify the conditioning regimen prior to HSCT. The most promising results have been obtained with radiolabeled anti-CD45 antibodies.