PD-1 blockade potentially enhances adoptive cytotoxic T cell potency in a human acute myeloid leukaemia animal model

Objectives: Acute myeloid leukaemia (AML) is a malignant haematological disease that remains difficult to cure. Cytotoxic T cell (CTL) adoptive infusion therapy may be conducive to tumour remission by boosting physical immunity. Furthermore, programmed death receptor-1 (PD-1) blockade immunotherapy has shown tremendous success in many cancer therapies. Method: We attempted to combine these two immunotherapy strategies to intervene in AML by generating AML cellspecific cytotoxic T lymphocytes in vitro and in vivo with an AML cell strain expressing specific antigens. Results: First, we observed that peripheral blood mononuclear cells (PBMCs) could be induced to generate large numbers of CD8(+) CTL cells through immune stimulation. In addition, these CD8(+) cells could effectively recognize a human AML cell line and exert cytotoxicity. In animal tests, PD-1 blockade combined with CTL infusion could induce significantly more AML tumour reduction than either treatment alone. This synergistic effect was thought to be connected to immune modulation enhancement, as regulatory T cells (Tregs) in the peripheral blood (PB) were found to be suppressed. Conclusions: This finding suggested the potential application of PD-1 blockade in AML. The present work demonstrated an excellent synergistic tumour therapeutic effect of PD-1 blockade and CTL therapy compared with either treatment alone.