三阴性乳腺癌（TNBC）是一种侵袭性乳腺癌亚型，预后较差，尤其是在转移性乳腺癌中。抗程序性细胞死亡蛋白 1/程序性死亡配体 1 (PD-L1) 免疫检查点抑制剂 (ICI) 联合化疗已证明在转移性 TNBC (mTNBC) 中具有良好的临床疗效，但仍存在未满足的需求。特别是对于 PD-L1 阴性肿瘤患者。 mTNBC 中 ICI 的耐药机制包括肿瘤微环境 (TME) 中存在免疫抑制性肿瘤相关巨噬细胞 (TAM)。 Eganelisib 是一种有效的、选择性的小分子 PI3K-γ 抑制剂，临床前研究表明，它可以通过减少骨髓细胞向肿瘤的募集、将 TAM 从免疫抑制性重编程为免疫激活表型以及增强 ICI 的活性来重塑 TME。这些研究为 2 期临床试验巨噬细胞重编程免疫肿瘤学 (MARIO-3，NCT03961698) 中一线 mTNBC 中 eganelisib 与抗 PD-L1 atezolizumab 和白蛋白结合型紫杉醇的联合临床评估提供了依据。我们在此首次展示 MARIO-3 研究的深入转化分析以及实体瘤 eganelisib 单药疗法 Ph1/b 研究的补充数据（MARIO-1，NCT02637531）。配对治疗前和治疗后肿瘤活检通过多重免疫荧光 (n=11)、使用 GeoMx 数字空间分析 (n=12) 的空间转录组学和 PD-L1 免疫组织化学 (n=18) 来分析免疫表型。使用流式细胞术和多重细胞因子分析对外周血样本进行分析。MARIO-3 的配对肿瘤活检结果揭示了 TAM 重编程、免疫激活和细胞外基质 (ECM) 重组的基因特征。对 PD-L1 阴性肿瘤的分析显示，ECM 基因特征在基线时升高，但在治疗后下降。无论基线 PD-L1 状态如何，都会观察到免疫激活的基因特征，并且发生在无进展生存期较长的患者中。外周血分析揭示了全身免疫激活。这是首个转化分析报告，包括首创 PI3K-γ 抑制剂 eganelisib 与 atezolizumab 和白蛋白结合型紫杉醇联合用于一线 mTNBC 的 2 期临床研究中的配对肿瘤活检。这些结果支持 eganelisib 作为 TAM 重编程免疫疗法的作用机制，并支持将 eganelisib 与 ICI 和化疗联合治疗 TAM 驱动的 ICI 耐药适应症的基本原理。© 作者（或其雇主）2024 . 根据 CC BY-NC 允许重复使用。禁止商业再利用。请参阅权利和权限。英国医学杂志出版。

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with a poor prognosis particularly in the metastatic setting. Treatments with anti-programmed cell death protein-1/programmed death-ligand 1 (PD-L1) immune checkpoint inhibitors (ICI) in combination with chemotherapies have demonstrated promising clinical benefit in metastatic TNBC (mTNBC) but there is still an unmet need, particularly for patients with PD-L1 negative tumors. Mechanisms of resistance to ICIs in mTNBC include the presence of immunosuppressive tumor-associated macrophages (TAMs) in the tumor microenvironment (TME). Eganelisib is a potent and selective, small molecule PI3K-γ inhibitor that was shown in preclinical studies to reshape the TME by reducing myeloid cell recruitment to tumors and reprogramming TAMs from an immune-suppressive to an immune-activating phenotype and enhancing activity of ICIs. These studies provided rationale for the clinical evaluation of eganelisib in combination with the anti-PD-L1 atezolizumab and nab-paclitaxel in firstline mTNBC in the phase 2 clinical trial MAcrophage Reprogramming in Immuno-Oncology-3 (MARIO-3, NCT03961698). We present here for the first time, in-depth translational analyses from the MARIO-3 study and supplemental data from eganelisib monotherapy Ph1/b study in solid tumors (MARIO-1, NCT02637531).Paired pre-treatment and post-treatment tumor biopsies were analyzed for immunophenotyping by multiplex immunofluorescence (n=11), spatial transcriptomics using GeoMx digital spatial profiling (n=12), and PD-L1 immunohistochemistry, (n=18). Peripheral blood samples were analyzed using flow cytometry and multiplex cytokine analysis.Results from paired tumor biopsies from MARIO-3 revealed gene signatures of TAM reprogramming, immune activation and extracellular matrix (ECM) reorganization. Analysis of PD-L1 negative tumors revealed elevated ECM gene signatures at baseline that decreased after treatment. Gene signatures of immune activation were observed regardless of baseline PD-L1 status and occurred in patients having longer progression-free survival. Peripheral blood analyses revealed systemic immune activation.This is the first report of translational analyses including paired tumor biopsies from a phase 2 clinical study of the first-in-class PI3K-γ inhibitor eganelisib in combination with atezolizumab and nab-paclitaxel in frontline mTNBC. These results support the mechanism of action of eganelisib as a TAM-reprogramming immunotherapy and support the rationale for combining eganelisib with ICI and chemotherapy in indications with TAM-driven resistance to ICI.© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.