We investigated how the graft-versus-leukemia (GVL) effect is attenuated in the tumor microenvironment using a murine model of non-myeloablative allo-HSCT (NM-HSCT) plus delayed donor leukocyte infusion (DLI) in a haploidentical B6→F1 strain combination. In-line with aggravated leukemia growth, the proportions of effector T cells expressing IFN-γ (Teffs) in spleen were reduced and attenuated GVL activity was found to be accompanied by a rebound in CD4(+)Foxp3(+) regulatory T cells (Tregs) in tumor-draining lymph nodes and tumor tissues. DLI-derived Tregs and Teffs may be potential indicators of presence of leukemic progression after DLI in this GVL model.
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