多药耐药性 1 (MDR1) 转运蛋白限制乳腺癌 (BC) 治疗中使用的化疗药物（紫杉醇、蒽环类药物）在细胞内的积累。除了肿瘤细胞外，MDR1 还在免疫细胞亚群上表达，并赋予化疗耐药性。在人类 T 细胞中，大多数 CD8 T 细胞和 CD4 T 辅助 (Th) 细胞亚群都表达 MDR1。在这里，我们探讨了 MDR1 在 CD4 T 细胞上的表达、功能和调节，并研究了该群体在 BC 中对新辅助化疗 (NAC) 的反应中的作用。通过流式细胞术检测 BC 患者。通过流式细胞术和 RNA 测序 (RNA-seq)，这些特征被扩展到来自未经治疗的乳腺肿瘤的 CD4 Th 细胞。我们进行了体外极化测定，以破译 MDR1 对 CD4 Th 细胞的调节。我们在体外评估了化疗药物对 MDR1 CD4 Th 细胞的影响。我们在两个独立的 BC 队列以及 NAC 前后 BC 肿瘤活检的公共 RNA-seq 数据集中分析了 NAC 治疗对血液和肿瘤中 MDR1 CD4 Th 细胞的影响及其与治疗效果的关联。最后，我们对接受 NAC 治疗的患者的血液 CD4 记忆 T 细胞进行了单细胞 (sc) RNAseq，并将其与 scRNAseq 公共数据集相结合。MDR1 CD4 Th 细胞在 Th1.17 多功能细胞中高度富集，但也在 Th17 细胞中富集，在血液和未经治疗的乳腺肿瘤组织中。从机制上讲，在体外 Th17 或 Th1.17 极化过程中，肿瘤生长因子 (TGF)-β1 是 MDR1 诱导所必需的。在 NAC 治疗的患者中，紫杉醇体外和体内治疗后，MDR1 表达赋予 Th1.17 和 Th17 细胞选择性优势。 scRNAseq 证明 MDR1 与肿瘤 Th1.17 和具有细胞毒性细胞特征的 Th 相关。血液和肿瘤中 MDR1 CD4 Th1.17 和 Th17 细胞的富集与病理反应呈正相关。 NAC 耐药患者缺乏 Th1.17 和 Th17 的早期调节，因此主张将其用作化疗方案调整的生物标志物。MDR1 有利于 NAC 后血液和肿瘤中 Th1.17 和 Th17 的富集，这与临床反应相关。 © 作者（或其雇主）2023。根据 CC BY-NC 允许重复使用。不得商业再利用。请参阅权利和权限。由英国医学杂志出版。

Multidrug resistance-1 (MDR1) transporter limits the intracellular accumulation of chemotherapies (paclitaxel, anthracyclines) used in breast cancer (BC) treatment. In addition to tumor cells, MDR1 is expressed on immune cell subsets in which it confers chemoresistance. Among human T cells, MDR1 is expressed by most CD8+ T cells, and a subset of CD4+ T helper (Th) cells. Here we explored the expression, function and regulation of MDR1 on CD4+ T cells and investigated the role of this population in response to neoadjuvant chemotherapy (NAC) in BC.Phenotypic and functional characteristics of MDR1+ CD4 Th cells were assessed on blood from healthy donors and patients with BC by flow cytometry. These features were extended to CD4+ Th cells from untreated breast tumor by flow cytometry and RNA-sequencing (RNA-seq). We performed in vitro polarization assays to decipher MDR1 regulation on CD4 Th cells. We evaluated in vitro the impact of chemotherapy agents on MDR1+ CD4+ Th cells. We analyzed the impact of NAC treatment on MDR1+ CD4+ Th cells from blood and tumors and their association with treatment efficacy in two independent BC cohorts and in a public RNA-seq data set of BC tumor biopsies before and after NAC. Finally, we performed single cell (sc) RNAseq of blood CD4+ memory T cells from NAC-treated patients and combined them with an scRNAseq public data set.MDR1+ CD4 Th cells were strongly enriched in Th1.17 polyfunctional cells but also in Th17 cells, both in blood and untreated breast tumor tissues. Mechanistically, Tumor growth factor (TGF)-β1 was required for MDR1 induction during in vitro Th17 or Th1.17 polarization. MDR1 expression conferred a selective advantage to Th1.17 and Th17 cells following paclitaxel treatment in vitro and in vivo in NAC-treated patients. scRNAseq demonstrated MDR1 association with tumor Th1.17 and Th with features of cytotoxic cells. Enrichment in MDR1+ CD4+ Th1.17 and Th17 cells, in blood and tumors positively correlated with pathological response. Absence of early modulation of Th1.17 and Th17 in NAC-resistant patients, argue for its use as a biomarker for chemotherapy regimen adjustment.MDR1 favored the enrichment of Th1.17 and Th17 in blood and tumor after NAC that correlated to clinical response.© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.