背景：细胞分裂周期34（Cell division cycle 34, CDC34）是一种E2泛素连接酶，参与底物蛋白的蛋白酶体降解，并能够稳定多种关键蛋白，包括表皮生长因子受体（Epidermal growth factor receptor , EGFR），从而促进肺癌等肿瘤的发生发展。研究表明，CDC34在多种癌症中表现出过表达，其在肿瘤细胞生长和存活中的重要作用已被广泛关注。然而，CDC34在肿瘤免疫微环境中的作用仍然不明确，尤其是在乳腺癌等实体肿瘤中的免疫逃逸机制中其潜在的作用尚未被深入探讨。

方法：本研究首先通过使用癌症基因组图谱（The Cancer Genome Atlas , TCGA）数据集，分析了CDC34在不同类型癌症中的表达情况，并评估了CDC34与免疫逃逸相关通路之间的关系。为进一步探讨CDC34在肿瘤免疫微环境中的具体作用，我们利用公开的单细胞RNA测序数据，分析了CDC34在乳腺癌样本中的表达情况及其对免疫细胞肿瘤浸润的影响。在细胞和小鼠模型中，我们通过沉默或过表达CDC34的细胞，研究了其对巨噬细胞吞噬活性及分化簇47（Cluster of differentiation 47, CD47）的调节作用。通过免疫共沉淀、蛋白质印迹和邻位连接技术分析（Proximity ligation assays, PLA），我们进一步探讨了CDC34与缺氧诱导因子1a（Hypoxia-inducible factor 1α, HIF1a）之间的相互作用。通过多重免疫组化（Multiplex immunohistochemistry,  mIHC）染色方法，评估了137例人乳腺癌样本中CDC34、CD47的表达及效应T细胞的浸润情况。

结果：通过对TCGA数据集的分析，我们发现CDC34在乳腺癌样本中呈显著上调，与患者的总生存期呈负相关。此外，CDC34的表达与巨噬细胞对癌细胞的吞噬活性呈负相关，表明CDC34在免疫逃逸中的潜在作用。进一步的实验结果显示，CDC34通过蛋白酶体泛素化途径稳定HIF1a，在转录水平上调癌细胞CD47表达，从而促进癌细胞逃避巨噬细胞的吞噬。抑制CDC34的表达能够显著增强巨噬细胞的吞噬活性，抑制肿瘤生长，并与抗PD-L1抗体在小鼠乳腺癌模型中产生抗肿瘤协同效应。进一步对临床样本分析显示，CDC34在137名乳腺癌患者中有66例（48.2%）表现出高表达，并与患者的总生存期呈负相关。CDC34的高表达与CD47的上调呈正相关，而与CD8⁺颗粒酶B阳性T细胞浸润呈负相关。在免疫治疗前的肿瘤样本中，免疫治疗的非应答者表现出较高的CDC34表达和较低的CD8⁺ T细胞肿瘤浸润率，与应答者相比具有显著差异。

结论：本研究揭示了CDC34在乳腺癌免疫逃逸中的关键作用，CDC34通过调控HIF1a-CD47轴，抑制巨噬细胞的吞噬活性，并通过抑制CD8⁺ T细胞的肿瘤浸润与激活，进一步削弱了适应性免疫反应。CDC34的双重作用使其成为乳腺癌免疫逃逸的重要调控因子，并且可能成为乳腺癌免疫治疗的潜在靶点。

Background: Cell division cycle 34 (CDC34) is an E2 ubiquitin-conjugating enzyme involved in the proteasomal degradation of substrate proteins. It can stabilize key proteins, including the epidermal growth factor receptor (EGFR), promoting the development of lung cancer and other malignancies. CDC34 is overexpressed in various cancers and plays a critical role in tumor cell growth and survival. However, its role in the tumor immune microenvironment, particularly in immune evasion mechanisms in solid tumors like breast cancer, remains poorly understood. Methods: This study analyzed CDC34 expression across different cancer types using the Cancer Genome Atlas (TCGA) dataset and examined its association with immune evasion pathways. To explore the role of CDC34 in the tumor immune microenvironment, we analyzed publicly available single-cell RNA sequencing data to assess CDC34 expression and its impact on immune cell infiltration in breast cancer samples. We also used cell and mouse models to investigate the regulatory effects of CDC34 on macrophage phagocytic activity and CD47 expression. Co-immunoprecipitation, Western blotting, and proximity ligation assays (PLA) were employed to examine interactions between CDC34 and hypoxia-inducible factor 1α (HIF1α). Additionally, we evaluated CDC34 and CD47 expression and effector T cell infiltration in 137 human breast cancer samples through multiplex immunohistochemistry. Results: TCGA dataset analysis revealed significant upregulation of CDC34 in breast cancer samples, which was negatively correlated with overall patient survival. CDC34 expression was also inversely correlated with macrophage phagocytic activity, indicating its potential role in immune evasion. Further experiments showed that CDC34 stabilizes HIF1α, which transcriptionally upregulates CD47 in cancer cells, leading to immune evasion by inhibiting macrophage phagocytosis. Silencing CDC34 significantly enhanced macrophage phagocytic activity, suppressed tumor growth, and produced a synergistic effect with anti-PD-L1 antibodies in a mouse breast cancer model. Analysis of clinical samples revealed that 48.2% of 137 breast cancer patients showed CDC34 overexpression, which was associated with poor survival. High CDC34 expression was correlated with elevated CD47 levels and reduced CD8+ granzyme B+ T cell infiltration. Notably, non responders to immunotherapy had higher CDC34 expression and lower CD8+ T cell infiltration compared to responders. Conclusion: This study highlights the crucial role of CDC34 in immune evasion in breast cancer. By regulating the HIF1α-CD47 axis, CDC34 suppresses macrophage phagocytic activity and inhibits CD8+ T cell infiltration and activation, further weakening the adaptive immune response. CDC34’s dual role makes it a key factor in immune evasion and a potential therapeutic target for breast cancer immunotherapy