Acquisition of suppressive function by CD4+ conventional T cells limits anti-tumor immunity driven by Treg depletion [RNA-seq]

Regulatory T (Treg) cells are essential for immune homeostasis but inhibit immune rejection of cancer. Strategies to disrupt Treg-mediated cancer immunosuppression have been met with limited clinical success, but the underlying mechanisms for this failure are poorly understood. By modeling Treg-targeted immunotherapy in mice, we find that a subset of CD4+ Foxp3- conventional T (Tconv) cells with potent suppressive function undergoes activation and expansion upon depletion of Foxp3+ Treg cells and limits therapeutic efficacy. We noted that Foxp3- Tconv cells within tumors adopt a Treg-like transcriptional profile upon Treg depletion and acquire suppressive function. This is attributable to a Th2-like subset of CD4+ Tconv cells marked by expression of (C-C motif) receptor 8 (CCR8) and enriched in Treg-associated transcripts. CCR8+ Tconv cells are found in mouse and human tumors. Upon Treg depletion, CCR8+ Tconv cells undergo systemic and intratumoral activation and expansion, resulting in IL-10 dependent suppression of anti-tumor immunity. Consequently, conditional deletion of Il10 within T cells augments anti-tumor efficacy upon Treg-depletion in mice, and antibody blockade of IL-10 signaling synergizes with Treg depletion to overcome treatment resistance. These findings reveal a secondary layer of immunosuppression by Tconv cells released upon therapeutic Treg depletion and suggest that broader consideration of suppressive function within the T cell lineage is required for development of effective Treg-targeted therapies. Overall design: Syngeneic B16-F10 melanoma cells were subcutaneously implanted into Foxp3EGFP-DTR mice and ablated Treg cells through administration of DTx. T cells were isolated by FACS and subjected to RNA-Seq analysis

调节性T（Regulatory T, Treg）细胞是维持免疫稳态的关键细胞群，但同时会抑制肿瘤的免疫排斥反应。旨在阻断Treg介导的肿瘤免疫抑制的治疗策略，临床转化成效始终有限，而其背后的失败机制尚未被充分阐明。本研究通过在小鼠体内构建靶向Treg的免疫治疗模型，发现一群具备强免疫抑制功能的CD4+ Foxp3- 常规T（conventional T, Tconv）细胞亚群，会在Foxp3+ Treg细胞被清除后发生活化与扩增，并限制治疗效果。我们观察到，肿瘤内的Foxp3- Tconv细胞在Treg细胞被清除后，会呈现出Treg样的转录组特征，并获得免疫抑制功能。这一现象可归因于一类以（C-C基序）受体8（C-C motif receptor 8, CCR8）表达为特征的CD4+ Tconv细胞的Th2样亚群，该亚群富含Treg相关的转录本。CCR8+ Tconv细胞可在小鼠与人类肿瘤中被检测到。当Treg细胞被清除后，CCR8+ Tconv细胞会发生全身性及瘤内的活化与扩增，进而通过依赖白细胞介素10（Interleukin-10, IL-10）的方式抑制抗肿瘤免疫反应。因此，在小鼠模型中，选择性敲除T细胞内的Il10基因可增强Treg清除疗法的抗肿瘤效果；而通过抗体阻断IL-10信号通路，可与Treg清除疗法产生协同作用，以克服治疗抗性。本研究揭示了治疗性清除Treg细胞后，被释放的Tconv细胞所介导的第二层免疫抑制机制，并提示开发高效的靶向Treg治疗策略时，需要更全面地考量T细胞谱系内的免疫抑制功能。实验设计：将同基因B16-F10黑色素瘤细胞皮下移植至Foxp3EGFP-DTR小鼠体内，通过注射白喉毒素（Diphtheria Toxin, DTx）清除Treg细胞。通过荧光激活细胞分选（Fluorescence-Activated Cell Sorting, FACS）分离T细胞，并进行RNA测序（RNA-Sequencing, RNA-Seq）分析。