NK cells play a significant role in immunosurveillance at the early stage of MLL-AF9 acute myeloid leukemia via CD226/CD155 interactions.

Acute myeloid leukemia (AML) is an aggressive hematological malignancy, and the mechanism underlying immune system involvement in leukemia development is unclear. In the present study, we utilized a myeloid/lymphoid or mixed-lineage leukemia; translocated to, 3 (MLLT3/MLL-AF9)-induced AML mouse model with or without exposure to irradiation. We found that the leukemia cells could survive and expand in hosts with intact immune systems, whereas leukemia progression was accelerated in mice with impaired immune systems. Moreover, the leukemia cells escaped from host immunosurveillance via editing their immunogenicity, including the up-regulation of an inhibitory antigen (i.e., CD47) and the down-regulation of active antigens (i.e., CD86, CD54, retinoic acid early transcript (RAE), histocompatibility 2, D region locus b (H2-Db) and H2-Dd). Natural killer (NK) cells were activated in the early phase of AML progression, whereas T cells were stimulated in the late phase. Furthermore, NK cell depletion showed that NK cells were necessary for the elimination of leukemia cells in our AML mouse model. Notably, CD155/CD226 primarily mediated the interaction between NK cells and leukemia cells and contributed to the antitumor effects of NK cells during the early phase of AML. Clinical data from patients with diverse hematological malignancies showed that CD155 expression was decreased in hematological malignancies. Taken together, our results demonstrate that NK cells play a pivotal role in immunosurveillance against leukemia cells during the early stage of AML primarily through the CD226/CD155 interaction; however, NK cells are not sufficient to eliminate leukemia cells.

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