Gallic acid potentiates the tumour-killing function of CD8+ T cells in gastric cancer.

[OBJECTIVE] To investigate the effect of gallic acid (GA) monomer on the cytotoxic function of tumour-infiltrating CD8+ T cells in gastric cancer and explore the underlying mechanisms.

[METHODS] Tumour-infiltrating CD8+ T cells were isolated from tumour tissues of patients with gastric adenocarcinoma using fluorescence-activated cell sorting. The purified CD8+ T cells were then co-incubated with GA at five different concentrations (0, 1, 2, 4, and 8 μM) for two incubation periods (24 and 48 h). Subsequently, the cytotoxic activity of tumour-infiltrating CD8+ T cells against gastric cancer cells was assessed using high-content live-cell tracking and cell counting assays. The apoptosis rates of gastric cancer cells were measured, and the expression of apoptosis-related factors caspase-3(p17), Bax, and Bcl-2 was analysed at both the transcriptional and protein levels. Additionally, secretion of IL-2, IL-4, IL-6, IFN-γ, TNF-α, and IL-17 by tumour-inflitrating CD8+ T cells was evaluated to elucidate the potential mechanisms of GA-mediated immunomodulation.

[KEY FINDINGS] GA significantly enhanced the tumour-killing capacity of tumour-infiltrating CD8+ T cells (cell viability: 51.64% in the intervention group vs. 100% in the control group at 48 h), leading to increased gastric cancer cell apoptosis (apoptotic rate: 38.81% in the intervention group vs. 15.19% in the control group). Western blot and qRT-PCR results showed that the apoptosis executor, caspase-3(p17), and apoptotic molecular switch, Bax, were increased, while the anti-apoptotic protein, Bcl-2, was decreased. The augmented cytotoxicity of tumour-infiltrating CD8+ T cells was associated with statistically significant elevated secretions of pro-inflammatory cytokines Interferon-γ (IFN-γ) (3.97 pg/ml in the intervention group vs. 3.12 pg/ml in the control group), Tumor Necrosis Factor-α (TNF-α) (4.45 pg/ml in the intervention group vs. 3.88 pg/ml in the control group), and Interleukin-2 (IL-2) (5.82 pg/ml in the intervention group vs. 5.22 pg/ml in the control group). In contrast, the expression of IL-17A (43.74 pg/ml in the intervention group vs. 49.38 pg/ml in the control group) and IL-6 (4.13 pg/ml in the intervention group vs. 4.61 pg/ml in the control group) showed statistically significant decreases.

[CONCLUSION] GA restored the impaired cytotoxic function of tumour-infiltrating CD8+ T cells in gastric cancer. These findings position GA as a potential novel immunomodulatory agent for improving anti-tumour immunity in gastric cancer treatment.