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B cell activating factor (BAFF) attenuates immunosuppressive monocytes in the melanoma tumor micro-environment

ABSTRACT: Emerging evidence indicates BAFF to be an important cytokine influencing anti-tumoral immunity. We generated a BAFF-overexpressing B16.F10 (BAFF) melanoma cell model and found that a significant survival advantage was conferred to C57BL/6 mice inoculated with BAFF cells. BAFF tumors had decreased myeloid infiltrates with lower PD-L1 expression. Monocyte depletion and anti-PD-L1 antibody treatment confirmed the functional significance on the phenotype. RNA-Seq analysis confirmed that monocytes isolated from BAFF tumors where characterized by a decreased exhaustive phenotype and enriched for in genes activating adaptive immune responses and NF- signaling. We wondered about the clinical relevance of BAFF plasma levels in melanoma patients. Evaluation of late stage metastatic melanoma patients treated with inhibitors of the PD-1/PD-L1 axis demonstrated a stratification of patients with high and low BAFF plasma levels, the former of which experienced lower responses to anti-PD-1 immunotherapies. In summary, we have shown that BAFF, through effects on tumor infiltrating monocytes not only impacts primary tumor growth but as biomarker can contribute to predicting response to anti-PD1 immunotherapy in later stages of advanced disease.

ORGANISM(S): Mus musculus

PROVIDER: GSE179670 | GEO | 2022/08/31

REPOSITORIES: GEO

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Project description:Tumor cells modulate host immunity by secreting extracellular vesicles (EV) and soluble factors in circulation. Their interactions with myeloid cells could lead to the generation of myeloid-derived suppressor cells (MDSC), which strongly inhibit the anti-tumor function of T and NK cells. We demonstrated previously that EV derived from mouse and human melanoma cells induced such immunosuppressive activity via upregulating the expression of programmed cell death ligand 1 (PD-L1) on myeloid cells that was dependent on the heat-shock protein 90a (HSP90a) in EV and on the toll-like receptor (TLR) on myeloid cells. Here, we investigated whether soluble HSP90α could convert monocytes into immunosuppressive MDSC. CD14+ monocytes were isolated from the peripheral blood of healthy donors, incubated with human rHSP90α alone or in the presence of inhibitors of TLR4 signaling and analyzed by flow cytometry. Inhibition of T cell proliferation assay was applied to assess immunosuppressive function of rHSP90α-treated monocytes. The concentration of HSP90α was measured by ELISA in plasma of advanced melanoma patients and correlated with clinical outcome. We found that the incubation of monocytes with rHSP90α for 16 h resulted in a strong upregulation of PD-L1 expression, whereas ROS and NO production as well as the expression of arginase-1, adenosine producing ectoenzymes CD39 and CD73 remained unchanged. The PD-L1 upregulation can be blocked by anti-TLR4 antibodies and an NF-κB inhibitor. After longer incubation (for 24h), rHSP90α-treated monocytes downregulated HLA-DR expression and acquired an augmented viability and resistance to apoptosis. Moreover, these monocytes were converted into MDSC indicated by their capacity to inhibit T cell proliferation mediated by TLR4 signaling as well as PD-L1 and indolamin-2,3-Dioxygenase (IDO) 1 expression. Higher levels of HSP90α in plasma of melanoma patients correlated with augmented PD-L1 expression on circulating monocytic (M) MDSC. Furthermore, melanoma patients with high levels of HSP90α displayed shorter progression-free survival (PSF) upon the treatment with immune checkpoint inhibitors (ICI).

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B cell activating factor (BAFF) attenuates immunosuppressive monocytes in the melanoma tumor micro-environment

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