The mechanisms underlying the efficacy of anti-programmed cell death protein 1 (PD-1) and anti-cytotoxic T lymphocyte-associated protein 4 (CTLA-4) therapy are incompletely understood. Here, by immune profiling responding PD-1⁺CD8⁺ T (T_Resp) cell populations from patients with advanced melanoma, we identified differential programming of T_Resp cells in response to combination therapy, from an exhausted toward a more cytotoxic effector program. This effect does not occur with anti-PD-1 monotherapy. Single-cell transcriptome and T cell receptor repertoire analysis was used to identify altered effector programming of expanding PD-1⁺CD8⁺ T cell clones with distinct regulon usage, STAT1 and STAT3 utilization and antitumor specificity connected to interleukin (IL)-21 signaling in combination and anti-CTLA-4 monotherapy. Therapeutic efficacy of CTLA-4 blockade was lost in B16F10 melanoma models with either Il21r⁻ deficiency or anti-IL-21 receptor blockade. Together, these results show how IL-21 signaling to T_Resp is critical for anti-CTLA-4-based checkpoint therapies and highlight major signaling differences to anti-PD-1 monotherapy.

抗程序性细胞死亡蛋白 1 （PD-1） 和抗细胞毒性 T 淋巴细胞相关蛋白 4 （CTLA-4） 治疗疗效的潜在机制尚不完全清楚。在这里，通过免疫分析反应来自晚期黑色素瘤患者的 PD-1 ⁺ CD8 ⁺ T （T _Resp ） 细胞群，我们确定了 T _Resp 细胞响应联合治疗的差异编程，从耗竭到更具细胞毒性的效应程序。这种效果不会发生在抗 PD-1 单药治疗中。单细胞转录组和 T 细胞受体库分析用于鉴定扩增的 PD-1 ⁺ CD8 ⁺ T 细胞克隆的效应程序改变，这些克隆具有不同的调节子使用、STAT1 和 STAT3 利用以及与白细胞介素 （IL）-21 信号传导联合抗 CTLA-4 单药治疗相关的抗肿瘤特异性。CTLA-4 阻断的治疗效果在 Il21r ⁻ 缺陷或抗 IL-21 受体阻断的 B16F10 黑色素瘤模型中丢失。总之，这些结果显示了 IL-21 信号转导对 _Resp 基于抗 CTLA-4 的检查点治疗至关重要，并突出了与抗 PD-1 单药治疗的主要信号转导差异。