Expressions of programmed death 1 and its ligand in acute myeloid leukemia patients and their effect on anti-tumor effect of programmed death receptor 1-positive natural killer cells in vitro / 白血病·淋巴瘤

ABSTRACT

Objective:To investigate the expression of programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) pathway in patients with acute myeloid leukemia (AML) and its relationship with clinical features and prognosis, and to examine its effect on PD-1-positive natural killer (NK) cells against AML cells in vitro.Methods:The bone marrow samples of 65 AML patients and the peripheral blood of 32 AML patients diagnosed in Affiliated Cancer Hospital of Zhengzhou University from July 2019 to December 2020 were prospectively collected, and the peripheral blood of 24 healthy people was taken as healthy control. The expression level of PD-L1 in bone marrow tumor cells and expression level of PD-1 in peripheral blood NK cells were detected by flow cytometry. The correlations of PD-1 expression in bone marrow tumor cells and PD-1 expression in NK cells with the clinicopathological features, curative effect and prognosis of patients were analyzed. Flow cytometry was used to detect the expression level of PD-L1 in AML cell line THP-1 (target cells) and the expression level of PD-L1 in NK cell line NKL (effector cells). THP-1 cells treated with and without 25 μmol/L of PD-L1 inhibitor fraxinellone were used as experimental group and control group, and co-cultured with NKL cells at different effector-to-target ratios. The apoptosis of THP-1 cells and the expression of NKG2D in NKL cells were detected by flow cytometry, the cell proliferation status was detected by CCK-8 and the cell proliferation inhibition rate was calculated; the levels of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) in the supernatant of co-culture system were detected by enzyme-linked immunosorbent assay (ELISA).Results:The proportion of AML patients with PD-L1-positive expression in bone marrow tumor cells was higher than that in the healthy control group [38.5% (25/65) vs. 8.3% (2/24), P = 0.029]. The proportion of AML patients with PD-1-positive expression in peripheral blood NK cells was higher than that in the healthy control group [40.6% (13/32) vs. 12.5% (3/24), P = 0.035]. There were no statistical differences in sex, age, hemogram, proportion of primordial cells, risk stratification, chromosomal karyotype, gene mutation (except NPM1 gene), fusion gene and French-American-British cooperative group (FAB) typing between patients with PD-L1 positive and negative in bone marrow tumor cells and between patients with PD-1 positive and negative in peripheral blood NK cells (all P > 0.05). In relapsed/refractory patients, the proportion of patients with PD-L1-positive expression in bone marrow tumor cells was higher than that in newly treated patients [58.8% (10/17) vs. 31.2% (15/48), P = 0.045]. There was no significant difference in the proportion of patients with PD-1-positive expression in peripheral blood NK cells between relapsed/refractory patients and newly treated patients [(38.5% (5/13) vs. 42.1% (8/19), P = 0.837]. There was no statistical difference in complete remission (CR) rate between PD-L1 positive and negative patients [69.6% (16/23) vs. 74.3% (26/35), P > 0.05]. There was no statistical difference in CR rate between PD-1 positive and negative patients [66.7% (8/12) vs. 70.6% (12/17), P > 0.05]. There was no statistical difference in recurrence rate after CR between PD-L1 positive and negative patients [12.5% (2/16) vs. 19.2% (5/26), P > 0.05]. There was no statistical difference in recurrence rate after CR between PD-1 positive and negative patients [25.0% (2/8) vs. 16.7% (2/12), P > 0.05]. Flow cytometry showed that the positive rate of PD-1 in NKL cells was (67±6)% and the positive rate of PD-L1 in THP-1 cells was (85±5)%. After co-culture with NKL cells, the apoptotic rate and proliferation inhibition rate of THP-1 cells were higher in the experimental group compared with the control group, the expression of NKG2D on the surface of NKL cells was elevated, and the levels of IFN-γ and TNF-α in the co-culture supernatant were increased. Conclusions:In AML patients, the expression of PD-L1 in bone marrow tumor cells is high, and the expression of PD-1 in peripheral blood NK cells is also high. The expression of PD-L1 in bone marrow tumor cells of relapsed/refractory AML patients is higher than that of newly treated patients. Inhibition of PD-L1 expression in THP-1 cells can enhance the tumor killing activity of NKL cells in vitro. The mechanism may be that inhibition of PD-L1 expression in THP-1 cells up-regulates the expression of NKL cell activated receptor NKG2D and promotes the secretion of IFN- γ and TNF- α.