Effect of monoamine oxidase A on anti-cancer immunity of CD8+ T cells in cholangiocarcinoma

Objective To investigate the effect of monoamine oxidase A (MAOA) in cholangiocarcinoma on anti-tumor immunity of CD8+ T cells. Methods We established stably inducible MAOA expression human cholangiocarcinoma cell lines by transfecting Tet-on 3G system. CD8+ T cells were isolated from peripheral blood donated by healthy donors. After coculture with above celllines for 48 h, CD8+ T cells were analyzed by flow cytometry to detect the expression of granzyme B, perforin, programmed death 1 (PD-1), cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), as well as apoptosis rate. Enzyme linked immunosorbent assay (ELISA) was applied to assess the excretion of IFN-γ from CD8+ T cells. Lactate dehydrogenase (LDH) test was performed to evaluate the cytotoxicity against the mixed cultured tumor cells by CD8+ T cells. Results CD8+ T cells in mock transfected groups expressed lower level of granzyme B (44.2% vs. 51.5%, P=0.000), perforin (51.8% vs. 74.3%, P=0.000), expressed higher level of PD-1 and CTLA-4 (81.70% vs. 21.30%, P=0.000; 16.00% vs. 8.49%, P=0.000 respectively), secreted fewer IFN-γ (7 562.0±927.5) pg/ml vs. (10 107.0±1 162.0) pg/ml, P=0.229) and had a higher apoptosis rate (26.43% vs. 13.35%, P=0.000), and the cytotoxicity CD8+ T cells was also suppressed [(12.70±1.49)% vs. (22.88±2.93)%, P=0.036]. Conclusion Down-regulation of MAOA in cholangiocarcinoma would impede anti-tumour immunity of CD8+ T cells. Key words: Monoamine oxidase A; Cholangiocarcinoma; CD8+ T cells; Tumor immunity