Abstract 5626: Acquisition of lymphatic phenotype in bone marrow endothelial progenitors is regulated by immunosuppressive Th2 cytokines

Abstract

Abstract Introduction: Myeloid-lymphatic endothelial progenitors (M-LECPs) significantly contribute to expansion of tumor lymphatics and metastasis to lymph nodes. Bone marrow (BM) generated M-LECPs are a subset of M2-type of tumor-associated macrophages (TAMs) that heavily infiltrate breast and other human cancers. The M2-type of TAMs is primarily induced by immunosuppressive Th2 cytokines IL-4, IL-13, and IL-10. The goal of this study was to determine whether Th2 factors also promote the lymphatic phenotype in precursors of M-LECPs. Methods: Mouse BM cells were differentiated into M-LECPs by priming with CSF-1 followed by activation of LPS-TLR4 pathway. Transcripts of IL-4, IL-13, and IL-10 were measured by qPCR, and their proteins secreted into conditioned medium were detected by ELISA. The levels of receptors for Th2 cytokines IL-4, IL-13, and IL-10 as well as for stem cells (CD117, Sca-1), M2-TAMs (CD204, CD206) and lymphatic endothelial cells (Lyve-1, podoplanin, integrin-9a, collectin-12 and stabilin-1) were quantified by qPCR and flow cytometry. Impact of TLR4 induced autocrine IL-10 pathway was determined by analyzing the surface markers and gene profiles of differentiated M-LECPs in the presence of IL-10 blocking or control antibodies. Tumor levels of Th2 cytokines and expression of Th2 receptors in Lyve-1+ progenitors were detected by ELISA and immunofluorescence, respectively. Results: More than 95% of myeloid precursors treated with CSF-1 and LPS upregulated all three Th2 receptors and IL-10 but not IL-4 or IL-13 ligands. All receptors were functional as indicated by upregulation of M2, immunosuppressive, lymphatic and stem markers in cells co-treated with exogenous Th2 ligands as compared with CSF-1 alone. Blocking autocrine IL-10 significantly suppressed both M2-specific and pro-lymphatic differentiation. Tumor-infiltrating M-LECPs expressed Th2 receptors as well as all corresponding ligands including IL-4 and IL-13 that were absent in the BM cells. Conclusion: These data present a novel evidence that activation of immunosuppressive Th2 pathways in BM myeloid precursors induces both the M2-type and lymphatic phenotype. Expansion of lymphatics can enhance tumor immunosuppression by physical removal of immunostimulatory cells. These findings suggest that targeting Th2 pathways can simultaneously relieve immunosuppression and inhibit differentiation of pro-lymphatic progenitors that promote metastasis. Citation Format: Maria Espinoza Gonzalez, Lisa Volk-Draper, Nihit Bhattarai, Sophia Ran. Acquisition of lymphatic phenotype in bone marrow endothelial progenitors is regulated by immunosuppressive Th2 cytokines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5626.