WT1-targeted dendritic cell vaccination as a postremission treatment to prevent or delay relapse in acute myeloid leukemia.

Abstract

2506 Background: Vaccination with tumor antigen-loaded dendritic cells (DC) holds promise for the adjuvant treatment of cancer. Methods: In a phase I/II trial, we investigated the effect of autologous DC vaccination in 17 patients with acute myeloid leukemia (AML) in remission but at very high risk of full relapse. Wilms’ tumor 1 protein (WT1) was chosen as immunotherapeutic target and introduced into the DC by mRNA electroporation. We are continuing a phase II trial, which is still recruiting. Results: Two out of 3 patients, who were in partial remission with chemotherapy-refractory disease, were brought into complete remission following 4 biweekly intradermal injections of WT1 mRNA-electroporated DC. In those 2 patients as well as in 6 other patients who were in complete remission but who had molecularly demonstrable residual disease, there was a return to normal of the AML-associated WT1 mRNA tumor marker following DC vaccination, compatible with reaching clinical and molecular remission in 8/17 patients. Among the 8 responders, there have been 2 relapses and 2 deaths. Of the 9 non-responders, 8 have relapsed and 7 have died. Of the 2 patients in partial remission who were brought into complete remission by DC vaccination, 1 has died following relapse. Median overall survival was 6 months in non-responders and 52 months in responders (p=0.0007). Median relapse-free survival was 3 months in non-responders as compared to 47 months in responders (p<0.0001). Clinical responses overall were correlated with elevated levels of activated natural killer (NK) cells post-vaccination. Long-term clinical responses, lasting for at least 3 years, were significantly correlated with an increase in polyepitope WT1-specific tetramer+ CD8+ T-cell frequencies. Conclusions: DC-based immunotherapy elicits both innate (NK) and adaptive (T cells) cellular responses correlated with clinical benefit. WT1 mRNA-transfected DC emerge as a feasible and effective strategy to control residual disease in AML, in particular as a post-remission treatment to prevent full relapse.