The vascular nature of lung-resident mesenchymal stem cells.

Human lungs bear their own reservoir of endogenous mesenchymal stem cells (MSCs). Although described as located perivascular, the cellular identity of primary lung MSCs remains elusive. Here we investigated the vascular nature of lung-resident MSCs (LR-MSCs) using healthy human lung tissue. LR-MSCs predominately reside within the vascular stem cell niche, the so-called vasculogenic zone of adult lung arteries. Primary LR-MSCs isolated from normal human lung tissue showed typical MSC characteristics in vitro and were phenotypically and functionally indistinguishable from MSCs derived from the vascular wall of adult human blood vessels (VW-MSCs). Moreover, LR-MSCs expressed the VW-MSC-specific HOX code a characteristic to discriminate VW-MSCs from phenotypical similar cells. Thus, LR-MSC should be considered as VW-MSCs. Immunofluorescent analyses of non-small lung cancer (NSCLC) specimen further confirmed the vascular adventitia as stem cell niche for LR-MSCs, and revealed their mobilization and activation in NSCLC progression. These findings have implications for understanding the role of MSC in normal lung physiology and pulmonary diseases, as well as for the rational design of additional therapeutic approaches.

Direct conversion of human fibroblasts into therapeutically active vascular wall-typical mesenchymal stem cells.

Cell-based therapies using adult stem cells are promising options for the treatment of a number of diseases including autoimmune and cardiovascular disorders. Among these, vascular wall-derived mesenchymal stem cells (VW-MSCs) might be particularly well suited for the protection and curative treatment of vascular damage because of their tissue-specific action. Here we report a novel method for the direct conversion of human skin fibroblasts towards MSCs using a VW-MSC-specific gene code (HOXB7, HOXC6 and HOXC8) that directs cell fate conversion bypassing pluripotency. This direct programming approach using either a self-inactivating (SIN) lentiviral vector expressing the VW-MSC-specific HOX-code or a tetracycline-controlled Tet-On system for doxycycline-inducible gene expressions of HOXB7, HOXC6 and HOXC8 successfully mediated the generation of VW-typical MSCs with classical MSC characteristics in vitro and in vivo. The induced VW-MSCs (iVW-MSCs) fulfilled all criteria of MSCs as defined by the International Society for Cellular Therapy (ISCT). In terms of multipotency and clonogenicity, which are important specific properties to discriminate MSCs from fibroblasts, iVW-MSCs behaved like primary ex vivo isolated VW-MSCs and shared similar molecular and DNA methylation signatures. With respect to their therapeutic potential, these cells suppressed lymphocyte proliferation in vitro, and protected mice against vascular damage in a mouse model of radiation-induced pneumopathy in vivo, as well as ex vivo cultured human lung tissue. The feasibility to obtain patient-specific VW-MSCs from fibroblasts in large amounts by a direct conversion into induced VW-MSCs could potentially open avenues towards novel, MSC-based therapies.