A Lactate-induced SREBF2-dependent genetic program drives an immunotolerant dendritic cell population during cancer progression [Spatial transcriptomics]

Dendritic cells (cDCs) are essential mediators of anti-tumor immunity. Cancers have developed mechanisms to render DCs dysfunctional within the tumor microenvironment. Utilizing CD63 as a unique surface marker, we demonstrate that mature regulatory DCs (mregDCs) suppress DC antigen cross-presentation while driving TH2 and regulatory T cell differentiation within tumor-draining lymph node tissues. Transcriptional and metabolic studies show that mregDC functionality is dependent upon the mevalonate biosynthetic pathway and the master transcription factor, SREBP2. Melanoma-derived lactate activates DC SREBP2 in the tumor microenvironment (TME) and drives mregDC development from conventional DCs. DC-specific genetic silencing and pharmacologic inhibition of SREBP2 promotes anti-tumor CD8+ T cell activation and suppresses melanoma progression. CD63+ mregDCs reside within the sentinel lymph nodes of melanoma patients. Collectively, this work describes a tumor-driven SREBP2-dependent program that promotes CD63+ mregDC development and function while serving as a promising therapeutic target for overcoming immune tolerance in the TME. scRNAseq of dendritic cells (DCs) sorted from the tumor draining lymph node or non-draining lymph node of Tyrosinase-driven Cre Recombinase BRAFV600E, PTEN-/- mice on a C57Bl6 background, as well as Dcs sorted from the inguinal lymph node of non-tumor bearing wildtype mice. Additionally, scATACseq was performed on DCs sorted from the tumor draining lymph node of Tyrosinase-driven Cre Recombinase BRAFV600E, PTEN-/- mice. scRNAseq was also performed on dendritic cells sorted from the sentinel lymph node of human melanoma patients in addition to spatial transcriptomics of the sentinel lymph node of human melanoma patients.

树突状细胞（dendritic cells, cDCs）是抗肿瘤免疫的核心介导因子。肿瘤已演化出多种机制，使肿瘤微环境中的树突状细胞功能失调。本研究以CD63作为独特的表面标志物，证实成熟调节性树突状细胞（mature regulatory DCs, mregDCs）可抑制树突状细胞的抗原交叉呈递，并在肿瘤引流淋巴结组织中促进辅助性T细胞2（TH2）及调节性T细胞的分化。转录组与代谢组研究显示，mregDC的功能依赖于甲羟戊酸生物合成通路及关键转录因子SREBP2。黑色素瘤分泌的乳酸可在肿瘤微环境（tumor microenvironment, TME）中激活树突状细胞的SREBP2，进而促使常规树突状细胞向mregDC分化。对SREBP2进行树突状细胞特异性基因沉默或药物抑制，可增强抗肿瘤CD8+ T细胞的活化并抑制黑色素瘤进展。CD63阳性的mregDC存在于黑色素瘤患者的前哨淋巴结中。综上，本研究揭示了一种肿瘤驱动的、依赖SREBP2的调控程序，该程序可促进CD63+ mregDC的生成与功能，同时有望成为逆转肿瘤微环境免疫耐受的潜在治疗靶点。本研究的单细胞RNA测序（scRNAseq）样本包括：从C57Bl6背景下、由酪氨酸酶（Tyrosinase）驱动Cre重组酶表达的BRAFV600E、PTEN敲除（PTEN-/-）小鼠的肿瘤引流淋巴结及非引流淋巴结中分选的树突状细胞，以及从无肿瘤野生型小鼠的腹股沟淋巴结中分选的树突状细胞。此外，本研究还对上述BRAFV600E、PTEN-/-小鼠的肿瘤引流淋巴结中分选的树突状细胞开展了单细胞ATAC测序（scATACseq）。同时，本研究还对人类黑色素瘤患者前哨淋巴结中分选的树突状细胞进行了单细胞RNA测序，并对该类患者的前哨淋巴结开展了空间转录组测序。