Stage‐related PD‐L1 expression in Kaposi sarcoma tumor microenvironment

Abstract

Abstract 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.