In the present manuscript, we identify PDGFRA(+)/SCA-1(+) bone marrow-derived mesenchymal stem cells (Pα(+)S MSCs) as KS spindle cell progenitors and we also identify pro-angiogenic environmental conditions typical of KS as critical for KSHV sarcomagenesis. The gene discussed is PDGFRA; the disease is Kaposi's sarcoma.