免疫检查点抑制剂 (ICIs) 已成为错配修复缺陷/微卫星不稳定性高 (dMMR/MSI-H) 结直肠癌 (CRC) 患者的标准治疗方法。然而，仍然缺乏对 ICI 反应的生物标志物。前瞻性入组了 42 名接受新辅助 PD-1 阻断治疗的 dMMR CRC 患者。为了确定新辅助治疗病理完全缓解（pCR）的生物标志物，我们分析了基于下一代测序的基因组和转录组图谱，以及基于多重免疫荧光（mIF）染色的免疫细胞密度。对我们之前的研究中的单细胞RNA测序和GSE178341以及mIF进行综合分析，以进一步探讨肿瘤微环境（TME）对pCR反应的重要性。肿瘤组织和血浆样本的肿瘤突变负担pCR 组和非 pCR 组之间的差异相当，而 HLA-DQA1 和 HLA-DQB1 在 pCR 组中显着过表达。基因特征富集分析显示，pCR组中T细胞受体途径、抗原呈递途径等途径显着富集。此外，较高的预先存在的 CD8 T 细胞密度与 pCR 反应相关（767.47/mm2 vs. 326.64/mm2，P=0.013 Wilcoxon 检验）。进一步整合分析显示，低PD-1表达的CD8 T细胞（PD-1lo CD8 T细胞）表达高水平的TRGC2、CD160、KLRB1以及低水平的增殖和耗竭基因，与pCR反应显着相关。 dMMR CRC 中的特征，特别是 CD8 T 细胞与 ICI 的 pCR 反应相关。 dMMR CRC 内 TME 的异质性可能有助于区分对新辅助 ICI 完全缓解的患者。

Immune checkpoint inhibitors (ICIs) have become the standard of care for patients with mismatch repair-deficient/microsatellite instability-high (dMMR/MSI-H) colorectal cancer (CRC). However, biomarkers of response to ICIs are still lacking.Forty-two patients with dMMR CRC treated with neoadjuvant PD-1 blockade were prospectively enrolled. To identify biomarkers of pathological complete response (pCR) to neoadjuvant therapy, we analyzed genomic and transcriptomic profiles based on next-generation sequencing, and immune cell density based on multiplex immunofluorescence (mIF) staining. An integrated analysis of single-cell RNA sequencing from our previous study and GSE178341, as well as mIF was performed to further explore the significance of the tumor microenvironment (TME) on pCR response.The tumor mutation burden of both tumor tissue and plasma blood samples was comparable between the pCR and non-pCR groups, while HLA-DQA1 and HLA-DQB1 were significantly overexpressed in the pCR group. Gene signature enrichment analysis showed that pathways including T cell receptor pathway, antigen presentation pathway were significantly enriched in the pCR group. In addition, higher pre-existing CD8+ T cell density was associated with pCR response (767.47 per.mm2 vs. 326.64 per.mm2, P=0.013 Wilcoxon test). Further integrated analysis showed that CD8+ T cells with low PD-1 expression (PD-1lo CD8+ T cells) expressing high levels of TRGC2, CD160, KLRB1 and low levels of proliferated and exhausted genes were significantly associated with pCR response.Immune-associated transcriptomic features, particularly CD8+ T cells were associated with pCR response to ICI in dMMR CRC. Heterogeneity of TME within dMMR CRC may help to discriminate patients with complete response to neoadjuvant ICI.