To date, the overall response rate of PD-1 blockade remains unsatisfactory, partially due to limited understanding of tumor immune microenvironment (TIME). B-cell lymphoma 9 (BCL9), a key transcription co-activator of the Wnt pathway, is highly expressed in cancers. By genetic depletion and pharmacological inhibition of BCL9 in tumors, we found that BCL9 suppression reduced tumor growth, promoted CD8⁺ T cell tumor infiltration, and enhanced response to anti-PD-1 treatment in mouse colon cancer models. To determine the underlying mechanism of BCL9’s role in TIME regulation, single-cell RNA-seq was applied to reveal cellular landscape and transcription differences in the tumor immune microenvironment upon BCL9 inhibition. CD155-CD226 and CD155-CD96 checkpoints play key roles in cancer cell/CD8⁺ T cell interaction. BCL9 suppression induces phosphorylation of VAV1 in CD8⁺ T cells and increases GLI1 and PATCH expression to promote CD155 expression in cancer cells. In The Cancer Genome Atlas database analysis, we found that BCL9 expression is positively associated with CD155 and negatively associated with CD226 expression. BCL9 is also linked to adenomatous polyposis coli (APC) mutation involved in patient survival following anti-PD-1 treatment. This study points to cellular diversity within the tumor immune microenvironment affected by BCL9 inhibition and provides new insights into the role of BCL9 in regulating CD226 and CD96 checkpoints

迄今为止，PD-1 阻断剂的总体反应率仍然不能令人满意，部分原因是对肿瘤免疫微环境 (TIME) 的了解有限。B 细胞淋巴瘤 9 (BCL9) 是 Wnt 通路的关键转录共激活因子，在癌症中高度表达。通过肿瘤中 BCL9 的基因耗竭和药理学抑制，我们发现 BCL9 抑制降低了肿瘤生长，促进了 CD8 ⁺ T 细胞肿瘤浸润，并增强了小鼠结肠癌模型对抗 PD-1 治疗的反应。为了确定 BCL9 在 TIME 调节中作用的潜在机制，应用单细胞 RNA-seq 来揭示 BCL9 抑制后肿瘤免疫微环境中的细胞景观和转录差异。CD155-CD226 和 CD155-CD96 检查点在癌细胞/CD8 ^{+中起关键作用}T细胞相互作用。BCL9 抑制诱导 CD8 ⁺ T 细胞中 VAV1 的磷酸化并增加 GLI1 和 PATCH 表达以促进癌细胞中 CD155 的表达。在癌症基因组图谱数据库分析中，我们发现 BCL9 表达与 CD155 呈正相关，与 CD226 表达呈负相关。BCL9 还与涉及抗 PD-1 治疗后患者生存的腺瘤性结肠息肉 (APC) 突变有关。该研究指出了受 BCL9 抑制影响的肿瘤免疫微环境中的细胞多样性，并为 BCL9 在调节 CD226 和 CD96 检查点中的作用提供了新的见解