IL-10-Engineered Human CD4(+) Tr1 Cells Eliminate Myeloid Leukemia in an HLA Class I-Dependent Mechanism

T regulatory cells (Tregs) play a key role in modulating T cell responses. Clinical trials showed that Tregs modulate graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, their ability to mediate anti-leukemic activity (graft-versus-leukemia [GvL]) is largely unknown. Enforced interleukin-10 (IL-10) expression converts human CD4(+) T cells into T regulatory type 1 (Tr1)-like (CD4(IL-10)) cells that suppress effector T cells in vitro and xenoGvHD in humanized mouse models. In the present study, we show that CD4(IL-10) cells mediate anti-leukemic effects in vitro and in vivo in a human leukocyte antigen (HLA) class I-dependent but antigen-independent manner. The cytotoxicity mediated by CD4(IL-10) cells is granzyme B (GzB) dependent, is specific for CD13(+) target cells, and requires CD54 and CD112 expression on primary leukemic target blasts. CD4(IL-10) cells adoptively transferred in humanized mouse models directly mediate anti-tumor and anti-leukemic effects. In addition, when co-transferred with peripheral blood mononuclear cells (PBMCs), CD4(IL-10) cells contribute to the GvL activity but suppress xenoGvHD mediated by the PBMCs. These findings provide for the first time a strong rationale for CD4(IL-10) cell immunotherapy to prevent GvHD and promote GvL in allo-HSCT for myeloid malignancies.