Hematopoietic stem cell transplantation represents a treatment option that can result in significant improvements, and in many cases cures, for a variety of hematologic malignancies. In the autologous and syngeneic HSCT settings, the efficacy is attributed almost solely to the ability of high-dose chemotherapy and radiotherapy to overcome resistant mechanisms within malignant cells; however, relapse of disease remains the primary reason for treatment failure. Relapse is significantly less in the allogeneic HSCT setting. This reduction in relapse rates is attributed to a T cell-mediated GVL effect, but it comes at the expense of GVHD, resulting in high treatment-related morbidity and mortality. Advances in the understanding of T cell biology and tumor immunology, which includes identification of immunogenic cancer antigens and an increased ability to identify and expand T cells with tumor reactivity, will lead to the translation of the GVL effect into the syngeneic and autologous HSCT settings. Current studies of adoptive cellular therapy in solid tumors, particularly melanoma, suggest that this is highly possible.110 In the allogeneic HSCT setting, the situation is somewhat reversed, as clinical applications and success at treating malignancy leads the scientific understanding of the biol-

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