PDGFRA and Kaposi's sarcoma: In contrast, KSHV-infected PDGFRA-positive (Pα(+)S) MSCs cultured in pro-angiogenic KS-like conditions (K-Pα(+)S KS) were the only cells to form colonies in soft agar (Fig 1E), suggesting that the KS-like culture conditions conferred malignant phenotypic characteristics to K-Pα(+)S MSCs.