What role does gemtuzumab ozogamicin have in the treatment of acute myelogenous leukemia?

Gemtuzumab ozogamicin (GO) is a novel, targeted chemotherapy designed to treat acute myeloid leukemia (AML). GO consists of an antitumor antibiotic, calicheamicin, linked to a humanized monoclonal antibody against CD33. It has been approved in the United States since 2000 to treat CD33+ AML in first relapse in older adults who are not candidates for cytotoxic therapy. Beyond this indication, the role of GO is evolving. Single-agent GO has a limited role in de novo AML. Incorporation of GO into standard induction treatment in de novo and relapsed AML is feasible. Comparative phase III studies of such an approach are ongoing. GO is associated with serious toxicities, such as infusional reactions, transient liver function test abnormalities, and veno-occlusive disease of the liver, especially in patients who undergo hematopoietic stem cell transplantation.

Preliminary Results of the Safety of Immunotherapy with Gemtuzumab Ozogamicin following Reduced Intensity Allogeneic Stem Cell Transplant in Children with CD33+ Acute Myeloid Leukemia

PURPOSE

Myeloablative allogeneic stem cell transplantation (SCT) has been successful in the treatment of childhood acute myeloid leukemia (AML), but may be associated with significant toxicity and recurrent disease. Reduced-intensity allogeneic SCT may offer a less toxic approach to patients with AML. Targeted immunotherapy with gemtuzumab ozogamicin has been shown to be safe, well tolerated in children, and, as a single agent, gemtuzumab ozogamicin has induced responses in 30% of patients with recurrent CD33+ AML. There are no safety data with gemtuzumab ozogamicin post allogeneic SCT in children. Therefore, we explored the feasibility and toxicity of targeted immunotherapy following reduced-intensity allogeneic SCT in children with CD33+ AML.

EXPERIMENTAL DESIGN

Eight patients with CD33+ AML received a reduced-intensity allogeneic SCT following fludarabine 30 mg/m2 for 6 days and busulfan 3.2 mg/kg (<4 years, 4 mg/kg/d) for 2 days. Donor sources included six 6/6 HLA-matched related peripheral blood stem cells, one 6/6 sibling cord blood, and one 4/6 unrelated cord blood.

RESULTS

Day 30 and day 60 donor chimerisms in seven of eight evaluable patients were 96 +/- 2% (n = 7) and 94 +/- 3% (n = 6), respectively. Five of six patients (too early for one patient) received two doses of gemtuzumab ozogamicin and one patient received only one dose. After each dose, all patients developed grade 4 neutropenia, with recovery on median days 16 and 13, respectively, after dose 1 and dose 2. Grade 4 thrombocytopenia was only observed in 2 of 11 gemtuzumab ozogamicin courses. No patients have developed dose-limiting toxicity secondary to gemtuzumab ozogamicin.

CONCLUSIONS

The administration of gemtuzumab ozogamicin post reduced-intensity allogeneic SCT in children with average risk AML is feasible and well tolerated with minimal toxicity. The maximal tolerated dose has yet to be determined for gemtuzumab ozogamicin post reduced-intensity allogeneic SCT in children with CD33+ AML. Additional studies in a larger group of patients will be required to adequately assess the safety of this approach.