The immunomodulatory role of tumor Syndecan-1 (CD138) on ex vivo tumor microenvironmental CD4(+) T cell polarization in inflammatory and non-inflammatory breast cancer patients

Herein, we aimed to identify the immunomodulatory role of tumor Syndecan-1 (CD138) in the polarization of CD4(+) T helper (Th) subsets isolated from the tumor microenvironment of inflammatory breast cancer (IBC) and non-IBC patients. Lymphocytes and mononuclear cells isolated from the axillary tributaries of non-IBC and IBC patients during modified radical mastectomy were either stimulated with the secretome as indirect co-culture or directly co-cultured with control and Syndecan-1-silenced SUM-149 IBC cells. In addition, peripheral blood mononuclear cells (PBMCs) of normal subjects were used for the direct co-culture. Employing flow cytometry, we analyzed the expression of the intracellular IFN-γ, IL-4, IL-17, and Foxp3 markers as readout for basal and co-cultured Th(1), Th(2), Th(17), and T(reg) CD4(+) subsets, respectively. Our data revealed that IBC displayed a lower basal frequency of Th(1) and Th(2) subsets than non-IBC. Syndecan-1-silenced SUM-149 cells significantly upregulated only T(reg) subset polarization of normal subjects relative to controls. However, Syndecan-1 silencing significantly enhanced the polarization of Th(17) and T(reg) subsets of non-IBC under both direct and indirect conditions and induced only Th(1) subset polarization under indirect conditions compared to control. Interestingly, qPCR revealed that there was a negative correlation between Syndecan-1 and each of IL-4, IL-17, and Foxp3 mRNA expression in carcinoma tissues of IBC and that the correlation was reversed in non-IBC. Mechanistically, Syndecan-1 knockdown in SUM-149 cells promoted Th(17) cell expansion via upregulation of IL-23 and the Notch ligand DLL4. Overall, this study indicates a low frequency of the circulating antitumor Th(1) subset in IBC and suggests that tumor Syndecan-1 silencing enhances ex vivo polarization of CD4(+) Th(17) and T(reg) cells of non-IBC, whereby Th(17) polarization is possibly mediated via upregulation of IL-23 and DLL4. These findings suggest the immunoregulatory role of tumor Syndecan-1 expression in Th cell polarization that may have therapeutic implications for breast cancer.