Autologous dendritic cell (DC) vaccination is a promising strategy for adjuvant cancer therapy in the setting of minimal residual disease (MRD). We performed a phase I/II trial in patients with acute myeloid leukemia (AML) where patients received intradermal injections of autologous DC loaded with mRNA coding for the Wilms' tumor protein (WT1). WT1 is highly overexpressed in leukemia and the level of WT1 RNA in peripheral blood is a useful biomarker for molecular diagnosis en follow-up in the MRD setting. We want to prospectively monitor WT1 RNA expression in the peripheral blood of vaccinated and non-vaccinated AML patients in order to evaluate its predictive value as a biomarker for relapse and to assess the clinical efficacy of DC vaccination in acute myeloid leukemia patients. We believe, on the basis of already available evidence, that the use of WT1 both as a target for immunotherapy as well as a biomarker not holds promise to assess the efficacy of new experimental therapeutic interventions such as DC vaccination.