CTLA-4 Blockade of Natural Killer Cells Increases Cytotoxicity against Acute Lymphoid Leukaemia Cells Neda

Objective: There is interest in using cytotoxic T lymphocyte antigen-4 (CTLA-4) immunotherapy to treat blood cancers.Unfortunately, patients with acute lymphoblastic leukaemia (ALL) frequently exhibit resistance to treatment and naturalkiller (NK) cell exhaustion. This study aims to increase the cytotoxic potency of natural killer cells by using CTLA-4 toblock the Nalm-6 leukaemia cell line.Materials and Methods: In this experimental study, NK cells were purified from the peripheral blood mononuclear cells(PBMCs) of 10 healthy people and assessed by flow cytometry for purity and viability. The purified cells were activatedovernight at 37°C and 5% CO2 with interleukin-15 (IL-15, 10 ng/ml) followed by evaluation of expressions of CTLA-4,activating and inhibitory receptors, and the release of interferon gamma (IFN-γ) and granzyme B (GZM B). CTLA-4expression on NK cells from recurrent ALL patients was also evaluated. Finally, the cytotoxic activity of NK cells wasassessed after the CTLA-4 blockade.Results: The purity of the isolated cells was 96.58 ± 2.57%. Isolated NK cells activated with IL-15 resulted in significantlyhigher CTLA-4 expression (8.75%, P lt;0.05). Similarly, CTLA-4 expression on the surface of NK cells from patientswith ALL was higher (7.46%) compared to healthy individuals (1.46%, P lt;0.05). IL-15 reduced NKG2A expression(P lt;0.01), and increased expressions of NKP30 (P lt;0.05) and NKP46 (P lt;0.01). The activated NK cells released moreIFN-γ (P lt;0.5) and GZM B (P lt;0.01) compared to unactivated NK cells. Blockade of CTLA-4 enhanced the NK cellkilling potential against Nalm-6 cells (56.3%, P lt;0.05); however, IFN-γ and GZM B levels were not statistically differentbetween the blocked and non-blocked groups.Conclusion: Our findings suggest that CTLA-4 blockage of Nalm-6 cells causes an increase in antitumour activity ofNK cells against these cells. Our study also provides evidence for the potential of cancer immunotherapy treatmentusing blocking anti-CTLA-4 mAbs.