Purpose: The therapeutic effect of allogeneic hematopoietic stem cell transplantation (HSCT) for patients with myeloid malignancies has been attributed in part to a graft-versus-leukemia effect that is dependent on donor T lymphocytes. CD8⁺ T-cell responses to MHC class I–restricted tumor epitopes, not just allogeneic antigens, may help mediate antileukemia effects after HSCT, but the specificity and function of such cells are not completely understood.

Experimental Design: We examined the diversity, phenotype, and functional potential of leukemia-associated antigen-specific CD8⁺ T cells in patients with myeloid leukemia following allogeneic HSCT. Screening for antigen-specific T cells was accomplished with a peptide/MHC tetramer library.

Results: Patients with acute myelogenous leukemia or chronic myelogenous leukemia in remission following HSCT exhibited significant numbers of peripheral blood CD8⁺ T cells that recognized varying combinations of epitopes derived from leukemia-associated antigens. However, these cells failed to proliferate, release cytokines, or degranulate in response to antigen-specific stimuli. As early as 2 months after HSCT, CD8⁺ T cells from patients were predominantly CD28⁻ CD57⁺ and had relatively short telomeres, consistent with cellular senescence.

Conclusions: Circulating leukemia-specific CD8⁺ T cells are prominent in myeloid leukemia patients after HSCT, but such cells are largely functionally unresponsive, most likely due to replicative senescence. These findings carry important implications for the understanding of the graft-versus-leukemia effect and for the rational design of immunotherapeutic strategies for patients with myeloid leukemias.