Increased Frequency and Vasculogenic Potential of Endothelial Colony-Forming Cells in Patients with Kaposi's Sarcoma.

Kaposi's sarcoma (KS) is characterized by hyperproliferation of spindle cells that have an endothelial origin and assume their characteristic features upon infection with human herpesvirus-8, the causative agent for KS. The multifocal nature of KS suggests that spindle cells derive from circulating HHV8-infected precursors that yet lack identification. We investigated whether endothelial colony-forming cells (ECFCs) obtained from KS patients may be putative precursors of spindle cells by assessing whether their in vitro behavior may evoke the in vivo behavior of KS spindle cells. We isolated and cultured ECFCs from the blood of 83 patients with classic KS and compared them with ECFCs obtained from 86 healthy donors. ECFCs were highly increased in the blood of classic KS patients; they showed higher proliferative and vasculogenic potential and higher production of IL-6 than control ECFCs. Similarly to spindle cells in KS lesions, a variable proportion of cells within each ECFC colony expressed the human herpesvirus-8 latency-associated nuclear antigen. ECFCs obtained from classic KS patients evoked KS spindle cell behavior, thus supporting the hypothesis that ECFCs may be putative precursors of spindle cells. ECFCs can therefore represent a noninvasive tool for studying KS and screening drug activity, thus possibly guiding personalized care for KS patients.