Stage related PD-L1 expression in Kaposi sarcoma tumor microenvironment.

Background The immune checkpoint molecule PD-L1 represents an important target in oncological immune therapy. The aim of our study was to evaluate PD-L1 expression and the composition of the tumor microenvironment (TME) in Kaposi sarcoma. Methods Immunohistochemical stains were performed for PD-L1, CD3, CD33, CD68, and CD168 in 24 Kaposi sarcoma samples. In PD-L1-positive cases, the double stains for PD-L1, CD31, podoplanin, and HHV8 were added. Results PD-L1 was observed in 71% of the samples and was predominantly located in the TME. PD-L1 expression was significantly higher in nodular stage than in patch/plaque stage. The TME consisted of CD68+/CD163+ -macrophages, CD33+ myloid-derived suppressor cells and monocytes and CD3+ T-cells. The TME showed a peritumoral distribution in nodular stage, in contrast to a diffuse distribution in patch/plaque stage. In 12 samples (50%), no plasma cells were found. Conclusion In nodular stage of KS, the TME is pushed back in the periphery of the tumor nodules. The PD-L1-positive TME between the tumor cells might protect them from the immune attack. An anti-PD-L1 treatment might be promising in KS patients.