Mesenchymal stem cells educate breast tumor associated macrophages to acquire increased immunosuppressive features

• Published in: The Journal of immunology (1950) Vol. 202; no. 1_Supplement; pp. 135 - 135.25
• Main Authors: BISWAS, SUBIR, Mandal, Gunjan, Chowdhury, Sougata Roy, Purohit, Suman, Payne, Kyle K., Galindo, Carmen Maria Anadon, Gupta, Arnab, Yu, Xiaoqing, Conejo-Garcia, Jose R., Bhattacharyya, Arindam
• Format: Journal Article
• Language: English
• Published: 01.05.2019
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.202.Supp.135.25

Abstract Breast cancer metastasis is known to be extensively promoted by immunosuppression. Here we describe a novel mechanism by which mesenchymal stem cell (MSC)-derived exosomes drive an immunosuppressive program within the breast tumor microenvironment. Initial q-PCR and immunophenotyping of human breast tumor samples, and TCGA data analysis confirmed a positive correlation between infiltrations of MSC and M2 macrophage phenotype, therefore we hypothesized that MSC promote M2 macrophage differentiation in breast tumors. We then performed a series of experiments in vitro and in vivo, and found that MSC-derived exosomes significantly promote differentiation of macrophages into PD-L1 expressing ‘M2-like’ phenotype, while also enhancing malignant progression of breast tumors, in vivo. Additionally, we observed increased invasive potential of tumor cells with higher expression of mesenchymal markers when induced with MSC-derived exosomes. Importantly, our observation of a significantly higher TGF-β production by tumor associated macrophages in exosome-induced tumors, with stronger PD-1 expression by intra-tumoral T cells, suggests TGF-β driven PD-1 upregulation. Blocking of PD-L1 abrogates exosome-induced tumor growth signifying the PD-L1/PD-1 checkpoint pathway is vital to MSC-induced tumor progression. Together, infiltration of MSCs within breast tumors drives the increased invasive potential as well as immune-checkpoint-mediated immunosuppression through inducing PD-L1 expression by tumor associated macrophages and PD-1 expression by T cells. Targeting infiltration of MSCs into the breast tumor therefore is a potential approach to reduce breast tumor metastases and improve efficacy of immunotherapies.