转移性黑素瘤引流淋巴结缺氧微环境诱导PD-L1阳性巨噬细胞的作用及其机制研究

Based on literature and our previous findings, hypoxia induced HIF-1α expression has been shown to be critical for the development of immune-suppressive microenvironment in melanoma. Hypoxia via HIF-1α overexpression promotes myeloid-derived suppressor cells (MDSCs) to express PD-L1, and differentiate into tumor-associated macrophages (TAMs), further facilitating tumor metastasis. Moreover, lymph node subcapsular sinus (SCS) CD169+ macrophages play an important role in preventing melanoma metastasis. However, whether hypoxia within tumor draining lymph nodes (TDLNs) of metastatic melanoma, has an impact on SCS CD169+ macrophages is unclear. We infer that elevated HIF-1α in melanoma TDLNs could increase PD-L1 expression on both SCS CD169+ and monocyte-derived macrophages and induce their differentiation into PD-L1+ macrophages with a TAM-like phenotype. Furthermore, these PD-L1+ macrophages could suppress the effector function of CD8+ T cells and affect the activation and function of Tregs, ultimately induce the immune suppressive microenvironment in TDLNs and promote melanoma metastasis. Therefore, lymph node samples from melanoma patients and mice model will be investigated to verify the hypothesis and reveal its underlying mechanism. This will provide a promising strategy in the immunotherapy of melanoma by targeting PD-L1+ macrophages.

文献报道及我们前期研究证明，缺氧时HIF-1α表达上调在黑素瘤肿瘤局部抑制性免疫微环境的形成中起重要作用。缺氧时MDSCs内HIF-1α表达上调可促进PD-L1表达，诱导其向TAM转化，促进肿瘤转移。SCS CD169+巨噬细胞在抑制黑素瘤转移中起重要作用。但黑素瘤发生淋巴结转移时，TDLNs中缺氧微环境是否对SCS CD169+巨噬细胞产生影响尚不清楚。我们推测转移性黑素瘤TDLNs缺氧微环境下，HIF-1α可上调SCS CD169+巨噬细胞和循环中单核细胞来源的巨噬细胞PD-L1的表达使之分化为PD-L1+巨噬细胞，进而向类似TAM的表型和功能转化，抑制CD8+T细胞的功能，同时影响Tregs的活化和功能，促进TDLNs中抑制性免疫微环境的形成和黑素瘤转移。基于此，本课题设计通过动物模型结合临床标本验证上述假设与揭示其机制，为以PD-L1+巨噬细胞为靶点的免疫治疗提供新的思路。

文献报道及我们的前期研究表明，缺氧时HIF-1α表达上调在黑素瘤肿瘤局部抑制性免疫微环境的形成中起重要作用。缺氧时MDSCs内HIF-1α表达上调可促进PD-L1表达，诱导其向TAM转化，促进肿瘤转移。近年来，研究发现缺氧条件下可激活细胞内TREM2相关信号通路。我们的研究证实，在人黑素瘤组织中有TREM2+巨噬细胞浸润。随黑素瘤模型鼠肿瘤进展，肿瘤组织局部的TREM2+巨噬细胞浸润增加，且高表达PD-L1和CD206，表现为免疫抑制表型，进而促进肿瘤进展。同时，我们的体外研究证实，TREM2高表达于M2型巨噬细胞，并可调控M2型巨噬细胞的表型和功能。为以TREM2+巨噬细胞为靶点的肿瘤免疫治疗提供了依据。最后，我们构建基于氧化锌的多功能纳米粒子靶向黑素瘤免疫抑制性微环境，能被TAMs在内的多种免疫细胞所吞噬摄取，产生免疫原性细胞死亡，激活树突状细胞，增加CD8+T细胞的浸润，进而高效杀伤肿瘤细胞并抑制黑素瘤转移。我们的研究不仅为以肿瘤相关巨噬细胞为靶点的免疫治疗提供了新的思路，并构建纳米载药系统高效抗肿瘤，促进黑素瘤免疫治疗的临床转化。

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