Fig. 5.

PD-L1 expression in CSC increases in the presence of MDSC in vitro and in vivo. a, b In vitro PD-L1 expression in ovarian cancer cells according to ALDH activity. Ovarian cancer cells were co-cultured with MDSC that had been isolated from spleens of mice bearing HM-1-GCSF-derived tumors. The EpCAM⁺ CD45⁻ cells were gated using flow cytometry and ALDH-high cells were then detected using an Aldefluor assay. After ALDH-high cells and ALDH-low cells were separately sorted by flow cytometry, the PD-L1 expression was compared by qRT-PCR. a Experimental schema. b PD-L1 expression assessed by qRT-PCR (n = 5). Bars, SD. *p < 0.05, according to two-sided Student’s t test. c The expression of ALDH1 and PD-L1 in ovarian cancer (mice model). The expression of ALDH1 (red) and PD-L1 (green) in HM-1-GCSF-derived tumors was assessed by immunofluorescence staining. The nuclei were stained with DAPI (blue). Images show typical co-expression of ALDH1 and PD-L1 (indicated with arrows). Bar, 20 μm. d The interactions between CSC and MDSC in the ovarian tumor microenvironment in mice. The expression of ALDH1 (red) and Ly6G (green) in HM-1-GCSF-derived tumors was assessed by immunofluorescence staining. The nuclei were stained with DAPI (blue). ALDH-high cells were located close to the Ly6G-positive cells in HM-1-GCSF-derived tumors. Bar, 20 μm