Patients with relapsed or refractory (r/r) acute myeloid leukemia (AML) have very poor long-term outcomes. Allogeneic stem cell transplantation (allo-SCT) can potentially cure some of these patients who are able to achieve a second or greater remission with salvage chemotherapy. Unfortunately, several barriers exist to transplantation and not all patients with r/r AML are able to proceed to allo-SCT. Therefore, novel therapies to decrease the risk of relapse in these patients are urgently needed. Wilms tumor 1 (WT1) protein has emerged as an encouraging vaccine target in AML due to its overexpression in leukemic blast cells and near absence in normal hematopoietic cells. Maintenance therapy with galinpepimut-S, a multivalent heteroclitic WT1 peptide vaccine, holds promise in early phase trials, in patients with AML by inducing a strong innate immune response against the WT1 antigen, leading to the design of this international, open-label, randomized clinical trial, named REGAL. Clinical trial registration: https://clinicaltrials.gov/study/NCT04229979. The clinical trial identifier is NCT04229979.