外泌体相关基因风险模型的鉴定，以评估三阴性乳腺癌的肿瘤免疫微环境并预测预后。

BACKGROUND: As a kind of small membrane vesicles, exosomes are secreted by most cell types from multivesicular endosomes, including tumor cells. The relationship between exosomes and immune response plays a vital role in the occurrence and development of tumors. Nevertheless, the interaction between exosomes and the microenvironment of tumors remains unclear. Therefore, we set out to study the influence of exosomes on the triple-negative breast cancer (TNBC) microenvironment. METHOD: One hundred twenty-one exosome-related genes were downloaded from ExoBCD database, and IVL, CXCL13, and AP2S1 were final selected because of the association with TNBC prognosis. Based on the sum of the expression levels of these three genes, provided by The Cancer Genome Atlas (TCGA), and the regression coefficients, an exosome risk score model was established. With the median risk score value, the patients in the two databases were divided into high- and low-risk groups. R clusterProfiler package was employed to compare the different enrichment ways between the two groups. The ESTIMATE and CIBERSORT methods were employed to analyze ESTIMATE Score and immune cell infiltration. Finally, the correlation between the immune checkpoint-related gene expression levels and exosome-related risk was analyzed. The relationship between selected gene expression and drug sensitivity was also detected. RESULTS: Different risk groups exhibited distinct result of TNBC prognosis, with a higher survival rate in the low-risk group than in the high-risk group. The two groups were enriched by immune response and biological process pathways. A better overall survival (OS) was demonstrated in patients with high scores of immune and ESTIMATE rather than ones with low scores. Subsequently, we found that CD4-activated memory T cells and M1 macrophages were both upregulated in the low-risk group, whereas M2 macrophages and activated mast cell were downregulated in the low-risk group in patients from the TCGA and GEO databases, respectively. Eventually, four genes previously proposed to be targets of immune checkpoint inhibitors were evaluated, resulting in the expression levels of CD274, CTLA4, LAG3, and TIM3 being higher in the low-risk group than high-risk group. CONCLUSION: The results of our study suggest that exosome-related risk model was related to the prognosis and ratio of immune cell infiltration in patients with TNBC. This discovery may make contributions to improve immunotherapy for TNBC.

背景：外泌体作为一种小膜囊泡，由包括肿瘤细胞在内的大多数细胞类型从多泡内体中分泌。外泌体与免疫反应之间的关系在肿瘤的发生和发展中起着至关重要的作用。然而，外泌体与肿瘤微环境之间的相互作用尚不清楚。因此，我们着手研究外泌体对三阴性乳腺癌（TNBC）微环境的影响。

方法：从 ExoBCD 数据库中下载了 121 个外泌体相关基因，最终选择了 IVL、CXCL13 和 AP2S1，因为它们与 TNBC 预后有关。基于 TCGA 提供的这三个基因的表达水平总和及其回归系数，建立了一个外泌体风险评分模型。根据两个数据库中患者的中位风险评分值，将其分为高风险组和低风险组。使用 R clusterProfiler 包比较两组之间的不同富集方式。采用 ESTIMATE 和 CIBERSORT 方法分析 ESTIMATE 评分和免疫细胞浸润。最后，分析免疫检查点相关基因表达水平与外泌体相关风险的相关性。还检测了选定基因表达与药物敏感性的关系。

结果：不同风险组的 TNBC 预后结果明显不同，低风险组的生存率高于高风险组。两组通过免疫反应和生物过程途径富集。与低评分组相比，高评分组的患者具有更好的总生存期（OS）。随后，我们发现 TCGA 和 GEO 数据库中的低风险组中 CD4 激活的记忆 T 细胞和 M1 巨噬细胞均上调，而低风险组中 M2 巨噬细胞和激活的肥大细胞下调。最后，评估了先前提出的四个作为免疫检查点抑制剂靶点的基因，结果表明低风险组中 CD274、CTLA4、LAG3 和 TIM3 的表达水平高于高风险组。

结论：本研究结果表明，外泌体相关风险模型与 TNBC 患者的预后和免疫细胞浸润比例有关。这一发现可能有助于改善 TNBC 的免疫治疗。