Bulk TCRseq analysis on CD8+ T cells in FSCN1-KI bone marrow chimera mice following anti-CD4 and anti-PDL1 mAb treatment. Bulk TCRseq analysis on CD8+ T cells in FSCN1-KI bone marrow chimera mice following anti-CD4 and anti-PDL1 mAb treatment

The repertoire of tumor-infiltrating T cells is a novel perspective to characterize effective anti-tumor T cell responses. Previous studies reported that the oligoclonal expansion in tumor T-cell repertoire is associated with anti-tumor effects. However, the contribution of the expansion of diverse T-cell clones remained unclear. We demonstrated that the polyclonal fraction of tumor-reactive T-cell repertoire consisting of relatively minor clones, increased in tumor-bearing mice treated with anti-PD-L1 or anti-CD4 monoclonal antibodies (mAbs), while the oligoclonal fraction consisting of major clones was unchanged. Moreover, the polyclonal fraction was enriched with progenitor exhausted T cells, essential for a durable anti-tumor response, and more dependent on CCR7+ migratory dendritic cells, responsible for priming tumor-reactive T cells in the tumor-draining lymph node (dLN). These results proposed that the expansion of diverse tumor-reactive clones, “clonal spreading,” is an important mechanism by which anti-PD-L1 and anti-CD4 treatments exert robust and durable anti-tumor T-cell responses. Overall design: CD8+ T cells from tumor, and CD8+ CD44high T cells from draining lymph node (dLN) were collected from B16F10 tumor-bearing Fscn1 knock-in BMC mice treated with anti-CD4 monoclonal antibody (mAb), anti-PD-L1 mAb or combination of anti-CD4 and anti-PD-L1 mAbs, with or without diphtheria toxin (DT) administration. Bulk TCR sequencing was performed, and T cell clones that overlap between tumor and dLN were identified.

肿瘤浸润T细胞库（tumor-infiltrating T cell repertoire）是表征有效抗肿瘤T细胞应答的全新视角。既往研究表明，肿瘤T细胞库中的寡克隆扩增（oligoclonal expansion）与抗肿瘤效应相关，然而多样化T细胞克隆扩增的具体贡献仍不明确。本研究证实，经抗PD-L1或抗CD4单克隆抗体（monoclonal antibodies, mAbs）处理的荷瘤小鼠（tumor-bearing mice）体内，由相对次要克隆构成的肿瘤反应性T细胞库多克隆组分（polyclonal fraction）占比升高，而由优势克隆构成的寡克隆组分则无显著变化。此外，该多克隆组分富含前体耗竭T细胞（progenitor exhausted T cells）——这类细胞对持久抗肿瘤应答至关重要，且更依赖于CCR7+迁移性树突状细胞（CCR7+ migratory dendritic cells）；后者负责在肿瘤引流淋巴结（tumor-draining lymph node, dLN）中致敏肿瘤反应性T细胞。上述结果表明，多样化肿瘤反应性克隆的扩增（即“克隆扩散（clonal spreading）”）是抗PD-L1与抗CD4治疗介导强效且持久抗肿瘤T细胞应答的重要机制。
实验设计：从经抗CD4单克隆抗体（mAb）、抗PD-L1 mAb或抗CD4与抗PD-L1 mAb联合处理，且予以或不予以白喉毒素（diphtheria toxin, DT）给药的B16F10荷瘤Fscn1敲入骨髓嵌合（BMC）小鼠中，分别分离肿瘤组织中的CD8+ T细胞（CD8+ T cells）以及引流淋巴结（dLN）中的CD8+ CD44高表达T细胞（CD44high T cells）。随后开展批量TCR测序（bulk TCR sequencing），并鉴定出肿瘤与dLN之间共有的T细胞克隆。