Expression of pro- and anti- apoptotic proteins and apoptosis in circulating CD8⁺ T cells of patients with the head and neck squamous cell carcinoma (SCCHN)

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Objectives: We have reported earlier that in patients with SCCHN, tumor-infiltrating lymphocytes and peripheral blood lymphocytes undergo spontaneous apoptosis leading to dysregulation of the immune system. While the death receptor-dependent pathway of apoptosis was suggested to be partially responsible for tumor-induced death, the mechanisms of spontaneous apoptosis of circulating T cells remain undefined. We studied the involvement of the mitochondria-dependent apoptotic pathway in the apoptosis of circulating T cells in patients with SCCHN. Methods: Peripheral blood mononuclear cells (PBMC) were obtained from 18 patients with SCCHN and 8 age- and sex-matched normal controls (NC). Multicolor flow cytometry was used to distinguish CD3⁺CD8⁺CCR7⁺ from CD3⁺CD8⁺CCR7^- cells, and Annexin V binding, bcl-2, bax and CD95 expression in these subsets were determined. The mitochondrial transmembrane potential (ΔΨm) was also measured in these T-cell subsets. Results: Relative to NC, the ratio of CD3⁺CD8⁺CCR7^- to CD3⁺CD8⁺CCR7⁺ T cells was significantly increased in patients with SCCHN (1.0 ± 0.5 vs 4.3 ± 4.0, p = 0.032), suggesting an expansion in the effector T-cell compartment. However, Annexin V binding to CD3⁺CD8⁺CCR7^- T-cell subset was significantly greater in patients than NC (51.5% ± 20.7 vs 24.7% ± 10.3, p = 0.002). Annexin V binding was also greater in the CD3⁺CD8⁺CCR7⁺ T-cell subset of patients relative to NC (33.5% ± 20.6 vs 5.4% ± 2.0, p < 0.001). In both CCR7⁺ and CCR7^- subsets of CD8+ T-cells, bax expression was increased relative to NC while that of bcl-2 remained unchanged and the bcl-2/bax ratio negatively correlated with Annexin V binding, while the bcl-2/bax ratio significantly downregulated only in CD3⁺CD8⁺CCR7⁺ T cell subset of patients as compared with NC (3.13 ± 0.99 vs 3.98 ± 0.48). Furthermore, CD95 expression significantly increased in patients relative to NC only in the CD3⁺CD8⁺CCR7⁺ T cell subset (42.5% ± 20.2 vs 12.1% ± 8.6, p < 0.001), suggesting a greater susceptibility to mitochondria- and Fas-mediated apoptosis of these cells. Interestingly, ΔΨm did not show differences between cancer patients and NC. Conclusion: The dysregulation of bax, a pro-apoptotic member of the bcl-2 family, strongly correlated with spontaneous apoptosis of CD3⁺CD8⁺ T cells in patients with SCCHN and this suggested that the mitochondrial pathway was involved in demise of these circulating cells, especially of the CD3⁺CD8⁺CCR7⁺ T-cell subset in patients with SCCHN.