PURPOSE: Treatment options are limited for patients with high-risk myelodysplastic syndrome (MDS). The azanucleosides, azacitidine and decitabine, are front-line therapy for MDS that induce promoter demethylation and gene expression of the highly immunogenic tumor antigen NY-ESO-1. We demonstrated that AML patients receiving decitabine exhibit induction of NY-ESO-1 expression in circulating blasts. We hypothesized that vaccinating against NY-ESO-1 in MDS patients receiving decitabine would capitalize upon induced NY-ESO-1 expression in malignant myeloid cells to provoke an NY-ESO-1-specific-MDS directed cytotoxic T-cell immune response. EXPERIMENTAL DESIGN: In a phase I study, 9 MDS patients received an HLA unrestricted NY-ESO-1 vaccine (CDX-1401 + poly-ICLC) in a non-overlapping schedule every four weeks with standard dose decitabine. RESULTS: Analysis of samples serially obtained from the 7 patients who reached the end-of-study demonstrated induction of NY-ESO-1 expression in 7/7 patients and NY-ESO-1 specific CD4+ and CD8+ T-lymphocyte responses in 6/7 and 4/7 of the vaccinated patients respectively. Myeloid cells expressing NY-ESO-1, isolated from a patient at different time-points during decitabine therapy, were capable of activating a cytotoxic response from autologous NY-ESO-1-specific T-lymphocytes. Vaccine responses were associated with a detectable population of CD141Hi conventional dendritic cells, which are critical for the uptake of NY-ESO-1 vaccine and have a recognized role in anti-tumor immune responses. CONCLUSION: These data indicate that vaccination against induced NY-ESO-1 expression can produce an antigen-specific immune response in a relatively non-immunogenic myeloid cancer and highlight the potential for induced-antigen directed immunotherapy in a group of patients with limited options.