In addition to CD4⁺ T cells and neutralizing antibodies, CD8⁺ T cells contribute to protective immune responses against SARS-CoV-2 in patients with coronavirus disease 2019 (COVID-19), an ongoing pandemic disease. In patients with COVID-19, CD8⁺ T cells exhibiting activated phenotypes are commonly observed, although the absolute number of CD8⁺ T cells is decreased. In addition, several studies have reported an upregulation of inhibitory immune checkpoint receptors, such as PD-1, and the expression of exhaustion-associated gene signatures in CD8⁺ T cells from patients with COVID-19. However, whether CD8⁺ T cells are truly exhausted during COVID-19 has been a controversial issue. In the present review, we summarize the current understanding of CD8⁺ T-cell exhaustion and describe the available knowledge on the phenotypes and functions of CD8⁺ T cells in the context of activation and exhaustion. We also summarize recent reports regarding phenotypical and functional analyses of SARS-CoV-2-specific CD8⁺ T cells and discuss long-term SARS-CoV-2-specific CD8⁺ T-cell memory.

除了 CD4 ⁺ T 细胞和中和抗体之外，CD8 ⁺ T 细胞还有助于 2019 年冠状病毒病 (COVID-19)（一种持续流行性疾病）患者针对 SARS-CoV-2 的保护性免疫反应。在 COVID-19 患者中，尽管 CD8 ⁺ T 细胞的绝对数量减少，但通常观察到表现出激活表型的 CD8 ⁺ T 细胞。此外，一些研究报告了抑制性免疫检查点受体（例如 PD-1）的上调，以及 COVID-19 患者的 CD8 ⁺ T 细胞中与衰竭相关的基因特征的表达。然而，CD8 ⁺ T细胞在COVID-19期间是否真正耗尽一直是一个有争议的问题。在本综述中，我们总结了目前对 CD8 ⁺ T 细胞耗竭的理解，并描述了在激活和耗竭背景下 CD8 ⁺ T 细胞的表型和功能的现有知识。我们还总结了最近有关 SARS-CoV-2 特异性 CD8 ⁺ T 细胞表型和功能分析的报告，并讨论了 SARS-CoV-2 特异性 CD8 ⁺ T 细胞的长期记忆。