The immune system exerts a protective role against cancer, mainly via the capacity of the CD8⁺ cytotoxic T lymphocytes to recognize and kill cancer cells.¹ However, cancer cells often develop mechanisms to escape the immune surveillance leading, thus, to the development of metastases.² One of the escape mechanisms is the activation of the programmed cell death-1 (PD-1) receptor, an inhibitory immune checkpoint, mostly expressed on the surface of T-cells. The engagement between the PD-1 receptor and its ligands, PD-L1 or PD-L2,³ results in the suppression of effector cell function via the induction of anergy, apoptosis, inhibition of their proliferation and secretion of inflammatory cytokines such as interferon gamma (IFN-γ), interleukin (IL)-4 and IL-2.⁴ PD-1 and PD-L1 are typically expressed on both activated and exhausted immune cells (ICs) and are upregulated under the influence of IFN-γ.⁵

中文翻译：

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未接受化疗的非小细胞肺癌中的 CD8+ PD-1+ T 细胞和 PD-L1+ 循环肿瘤细胞：它们的临床相关性？

免疫系统对癌症发挥保护作用，主要是通过CD8 ⁺细胞毒性 T 淋巴细胞识别和杀死癌细胞的能力。¹然而，癌细胞通常会发展出逃避免疫监视的机制，从而导致转移的发展。²逃逸机制之一是激活程序性细胞死亡-1 (PD-1) 受体，这是一种抑制性免疫检查点，主要在 T 细胞表面表达。PD-1 受体与其配体 PD-L1 或 PD-L2, ^{3之间的结合导致}通过以下途径抑制效应细胞功能诱导无反应性、细胞凋亡、抑制其增殖和炎性细胞因子如干扰素 γ (IFN-γ)、白细胞介素 (IL)-4 和 IL-2 的分泌。⁴ PD-1 和 PD-L1 通常在激活和耗尽的免疫细胞 (IC) 上表达，并在 IFN-γ 的影响下上调。⁵