Delimiting CD34+ Stromal Cells/Telocytes Are Resident Mesenchymal Cells That Participate in Neovessel Formation in Skin Kaposi Sarcoma

Kaposi sarcoma (KS) is an angioproliferative lesion in which two main KS cell sources are currently sustained: endothelial cells (ECs) and mesenchymal/stromal cells. Our objective is to establish the tissue location, characteristics and transdifferentiation steps to the KS cells of the latter. For this purpose, we studied specimens of 49 cases of cutaneous KS using immunochemistry and confocal and electron microscopy. The results showed that delimiting CD34+ stromal cells/Telocytes (CD34+SCs/TCs) in the external layer of the pre-existing blood vessels and around skin appendages form small convergent lumens, express markers for ECs of blood and lymphatic vessels, share ultrastructural characteristics with ECs and participate in the origin of two main types of neovessels, the evolution of which gives rise to lymphangiomatous or spindle-cell patterns—the substrate of the main KS histopathological variants. Intraluminal folds and pillars (papillae) are formed in the neovessels, which suggests they increase by vessel splitting (intussusceptive angiogenesis and intussusceptive lymphangiogenesis). In conclusion, delimiting CD34+SCs/TCs are mesenchymal/stromal cells that can transdifferentiate into KS ECs, participating in the formation of two types of neovessels. The subsequent growth of the latter involves intussusceptive mechanisms, originating several KS variants. These findings are of histogenic, clinical and therapeutic interest.