The immunological graft-versus-leukemia (GVL) effect seen after allogeneic stem cell transplantation suggests that stimulating the patient's own T cell responses to hematological malignancies might also retard disease progression and even achieve disease remissions. Wilm's Tumor 1 (WT1) was identified as a target vaccine antigen because this antigen is over-expressed by cluster of differentiation 34 (CD34) plus stem cells of most patients with myeloid and lymphoid malignancies but not by normal marrow cells. A human leukocyte antigen (HLA-A0201) restricted peptide derived from the Wilm's Tumor (WT) protein is anticipated to induce T cell response against MDS and leukemic cells while sparing normal cells. Of note, about 40% of the population is HLA-A0201 positive.