Phase II Trial of WT1 Analog Peptide Vaccine in Patients with Acute Myeloid Leukemia (AML) in Complete Remission (CR)

Abstract 3624

WT1 is a transcription factor which has been implicated in leukemogenesis and has been used as a marker of minimal residual disease (MRD). We previously demonstrated the feasibility of vaccinating AML patients in CR with a multivalent WT1 peptide vaccine and inducing immune responses. In an effort to further explore the safety and efficacy of this approach, we are conducting a Phase II study in which the vaccine is administered to AML patients in first CR and who completed all planned postremission chemotherapy. Eligible patients had WT1 transcript detectable by RT-PCR. The vaccine consisted of 4 native and derived WT1 peptides administered with the immune adjuvants Montanide and GM-CSF. Patients received 6 vaccinations over 10 weeks. Early toxicity was assessed at weeks 2 and 4. Immune responses were evaluated at week 12 by CD4+ T cell proliferation, CD3+ T cell interferon-g interferon release (ELISPOT) and WT1 peptide tetramer staining. Patients who were clinically stable and without disease recurrence could continue with up to 6 more vaccinations administered approximately every month. To date, 12 patients have been accrued to the study (6-M, 6-F; median age – 66 years, range 26–73 years). Cytogenetic subtypes varied among the study patients (Favorable-3, Intermediate-5, Unfavorable-4). The median time to vaccination after achieving CR was 7.5 months (range: 3–22 months). One patient was removed early because of relapse prior to receiving the first vaccination. Four patients have received at least 6 vaccines and 2 others have completed 12 vaccinations. Eight patients are alive without evidence of disease. One of these patients has an HLA-A02 subtype and was found to have developed T cells reactive with WT1-A (native peptide) HLA tetramers following 6 vaccinations which persisted (at a lower level) until after the 12th vaccination. Three patients relapsed during vaccination (after 1, 5 and 11 vaccines) and 2 of the 3 have died. Two of the relapsed patients who had sample available for immunologic evaluation, did not develop a CD4+ response to any of the peptides tested. Two other patients discontinued vaccination because of toxicity (hypersensitivity/pain with GM-CSF administration). Both remain in CR. No episodes of anaphylaxis or generalized urticaria were observed. Neither median disease free survival nor overall survival has been reached in this small cohort of patients. These preliminary findings demonstrate that the WT1 peptide vaccine is relatively well tolerated and has immunologic activity. Trial accrual is ongoing and further follow-up is required before any beneficial effect on outcome can be determined.