Minor histocompatibility antigens (mHags) play a major role in graft rejection, the induction of detrimental graft-vs-host disease (GVHD), and the development of the beneficial graft-vs-leukemia (GVL) effect after allogeneic stem cell transplantation (SCT). mHags can be defined as amino acid polymorphisms in cellular proteins that can lead to differential presentation of antigenic peptides in HLA molecules and therefore to differential recognition by T cells. The tissue distribution of the mHags and the HLA molecules by which they can be presented play a significant role in the clinical outcome of T-cell responses against these antigens. In part, differential recognition by T cells of mHags specifically expressed in hematopoietic cells, including the malignant cells from the recipient may result in GVL reactivity without concurrent GVHD. Furthermore, T-cell responses against proteins solely expressed in hematopoietic cell lineages from which the malignancy is derived may be appropriate mediators of GVL reactivity without GVHD induction. Characterization of clinical immune responses in patients treated for relapsed leukemia after allogeneic SCT with donor lymphocyte infusion in the absence of GVHD may lead to the characterization of new mHags that can be exploited to generate tumor-specific immune responses. By in vitro generation of T-cell responses against defined mHags, the efficacy and specificity of cellular immunotherapy against hematologic malignancies in the context of allogeneic transplantation may be improved.