Generation of functional blood vessels from a single c-kit+ adult vascular endothelial stem cell

Isolation of vascular endothelial cells from intact and injured murine brain cortex-technical issues and pitfalls in FACS analysis of the nervous tissue

CNS endothelial cells (CNS-ECs), one of the main non-neural CNS cell populations, play a vital role in physiology, pathology, and regeneration of the nervous system. Therefore, there is an urgent need to enhance our knowledge on their biology to elucidate mechanisms responsible for the blood brain barrier function in normal and pathological conditions, interaction between brain endothelium and neural stem cells in the neurogenic niche, the paracrine processes in the brain and spinal cord, etc. Here, we described a novel, simple, and efficient protocol for isolation of endothelial, vessel-forming cells from the murine CNS, which is based on Sca-1 expression. Using this newly described protocol we were able to detect and sort viable, highly pure CNS-ECs with minimal contamination by cells of non-endothelial origin. This method will increase the availability of CNS-ECs for in vitro research. Moreover, we compared phenotype of CNS-ECs isolated from neonatal mice and adult intact and injured brain looking for the cells of endothelial precursor characteristic, such as those found in the bone marrow and circulating in the bloodstream after organ injuries. We have found that neonatal brain capillaries contain proportion of endothelial precursor cells (Sca-1(+) , CD45(-) , c-Kit(+) ). Such precursors were also found in adult brain cortex, both in intact and injured brain. Finally, we discuss several crucial technical issues concerning CNS tissue preparation for flow cytometry analysis and cell sorting as well as nonspecific antibody binding caused by inflammatory microglia/macrophages which should be avoided in order to reliable isolation of pure CNS cells for downstream procedures including cell transplantation-based translational studies.

Endothelial progenitor cells and vascular repair

PURPOSE OF REVIEW

This review identifies recent advances in the field of vascular repair by regenerative endothelial cells and endothelial progenitor cells (EPCs).

RECENT FINDINGS

A growing number of studies indicate that bone marrow-derived circulating EPCs do not engraft into blood vessels, but that such circulating cells may regulate vascular repair via paracrine mechanisms. Novel modes of paracrine regulation are being uncovered, such as the release of endothelial cell-derived microparticles or microvesicles that contain microRNAs which can promote vascular repair. Instead of circulating cells, tissue-resident endothelial cells or EPCs may primarily drive the restoration of vascular function after endothelial injury. In addition to the generation of endothelial cells/EPCs from pluripotent stem cells, direct reprogramming of fibroblasts to endothelial cells/EPCs is becoming an important source of regenerative vascular cells.

SUMMARY

Ongoing efforts to understand the mechanisms that regulate vascular repair by resident regenerative vascular cells as well as their generation from fibroblasts and pluripotent stem cells will form the basis of future regenerative therapies.

Curtailing endothelial TGF-β signaling is sufficient to reduce endothelial-mesenchymal transition and fibrosis in CKD

Excessive TGF-β signaling in epithelial cells, pericytes, or fibroblasts has been implicated in CKD. This list has recently been joined by endothelial cells (ECs) undergoing mesenchymal transition. Although several studies focused on the effects of ablating epithelial or fibroblast TGF-β signaling on development of fibrosis, there is a lack of information on ablating TGF-β signaling in the endothelium because this ablation causes embryonic lethality. We generated endothelium-specific heterozygous TGF-β receptor knockout (TβRII(endo+/-)) mice to explore whether curtailed TGF-β signaling significantly modifies nephrosclerosis. These mice developed normally, but showed enhanced angiogenic potential compared with TβRII(endo+/+) mice under basal conditions. After induction of folic acid nephropathy or unilateral ureteral obstruction, TβRII(endo+/-) mice exhibited less tubulointerstitial fibrosis, enhanced preservation of renal microvasculature, improvement in renal blood flow, and less tissue hypoxia than TβRII(endo+/+) counterparts. In addition, partial deletion of TβRII in the endothelium reduced endothelial-to-mesenchymal transition (EndoMT). TGF-β-induced canonical Smad2 signaling was reduced in TβRII(+/-) ECs; however, activin receptor-like kinase 1 (ALK1)-mediated Smad1/5 phosphorylation in TβRII(+/-) ECs remained unaffected. Furthermore, the S-endoglin/L-endoglin mRNA expression ratio was significantly lower in TβRII(+/-) ECs compared with TβRII(+/+) ECs. These observations support the hypothesis that EndoMT contributes to renal fibrosis and curtailing endothelial TGF-β signals favors Smad1/5 proangiogenic programs and dictates increased angiogenic responses. Our data implicate endothelial TGF-β signaling and EndoMT in regulating angiogenic and fibrotic responses to injury.

The Wilms' tumour suppressor Wt1 is a major regulator of tumour angiogenesis and progression

Angiogenesis, activation of metastasis and avoidance of immune destruction are important for cancer progression. These biological capabilities are, apart from cancer cells, mediated by different cell types, including endothelial, haematopoietic progenitor and myeloid-derived suppressor cells. We show here that all these cell types frequently express the Wilms' tumour suppressor Wt1, which transcriptionally controls expression of Pecam-1 (CD31) and c-kit (CD117). Inducible conditional knockout of Wt1 in endothelial, haematopoietic and myeloid-derived suppressor cells is sufficient to cause regression of tumour vascularization and an enhanced immune response, leading to decreased metastasis, regression of established tumours and enhanced survival. Thus, Wt1 is an important regulator of cancer growth via modulation of tumour vascularization, immune response and metastasis formation.

Circulating mouse Flk1+/c-Kit+/CD45- cells function as endothelial progenitors cells (EPCs) and stimulate the growth of human tumor xenografts

Background

Endothelial progenitor cells (EPCs) have been demonstrated to have stem-cell like as well as mature endothelial functions. However, controversy remains as to their origins, immunophenotypic markings, and contribution to the tumor vascular network and tumor survival.

Methods

Flow cytometric analysis and sorting was used to isolate Flk-1+/c-Kit+/CD45- cells. Matrigel and methycellulose assays, flow cytometry, and gene array analyses were performed to characterize several murine EPC cell populations. Human tumor xenografts were used to evaluate the impact of EPCs on tumor growth and vascular development.

Results

Flk-1+/c-Kit+/CD45- cells were present at low levels in most murine organs with the highest levels in adipose, aorta/vena cava, and lung tissues. Flk-1+/c-Kit+/CD45- cells demonstrated stem cell qualities through colony forming assays and mature endothelial function by expression of CD31, uptake of acLDL, and vascular structure formation in matrigel. High passage EPCs grown in vitro became more differentiated and lost stem-cell markers. EPCs were found to have hemangioblastic properties as demonstrated by the ability to rescue mice given whole body radiation. Systemic injection of EPCs increased the growth of human xenograft tumors and vessel density.

Conclusions

Flk-1+/C-Kit+/CD45- cells function as endothelial progenitor cells. EPCs are resident in most murine tissue types and localize to human tumor xenografts. Furthermore, the EPC population demonstrates stem-cell and mature endothelial functions and promoted the growth of tumors through enhanced vascular network formation. Given the involvement of EPCs in tumor development, this unique host-derived population may be an additional target to consider for anti-neoplastic therapy.

Endothelial progenitor cells: from senescence to rejuvenation

Discovered more than 15 years ago, endothelial progenitor cells attract both basic and translational researchers. It has become clear that they represent a heterogeneous population of endothelial colony-forming cells, early or late outgrowth endothelial cells, or blood outgrowth endothelial cells, each characterized by differing proliferative and regenerative capacity. Scattered within the vascular wall, these cells participate in angiogenesis and vasculogenesis and support regeneration of epithelial cells. There is growing evidence that this cell population is impaired during the course of chronic cardiovascular and kidney disease when it undergoes premature senescence and loss of specialized functions. Senescence-associated secretory products released by such cells can affect the neighboring cells and further exacerbate their regenerative capacity. For these reasons, adoptive transfer of endothelial progenitor cells is being used in more than 150 ongoing clinical trials of diverse cardiovascular diseases. Attempts to rejuvenate this cell population either ex vivo or in situ are emerging. The progress in this field is paramount to regenerate the injured kidney.

In utero depletion of fetal hematopoietic stem cells improves engraftment after neonatal transplantation in mice

Although in utero hematopoietic cell transplantation is a promising strategy to treat congenital hematopoietic disorders, levels of engraftment have not been therapeutic for diseases in which donor cells have no survival advantage. We used an antibody against the murine c-Kit receptor (ACK2) to deplete fetal host hematopoietic stem cells (HSCs) and increase space within the hematopoietic niche for donor cell engraftment. Fetal mice were injected with ACK2 on embryonic days 13.5 to 14.5 and surviving pups were transplanted with congenic hematopoietic cells on day of life 1. Low-dose ACK2 treatment effectively depleted HSCs within the bone marrow with minimal toxicity and the antibody was cleared from the serum before the neonatal transplantation. Chimerism levels were significantly higher in treated pups than in controls; both myeloid and lymphoid cell chimerism increased because of higher engraftment of HSCs in the bone marrow. To test the strategy of repeated HSC depletion and transplantation, some mice were treated with ACK2 postnatally, but the increase in engraftment was lower than that seen with prenatal treatment. We demonstrate a successful fetal conditioning strategy associated with minimal toxicity. Such strategies could be used to achieve clinically relevant levels of engraftment to treat congenital stem cell disorders.

Characteristic of c-Kit+ progenitor cells in explanted human hearts

According to literature data, self-renewing, multipotent, and clonogenic cardiac c-Kit⁺ progenitor cells occur within human myocardium. The aim of this study was to isolate and characterize c-Kit⁺ progenitor cells from explanted human hearts. Experimental material was obtained from 19 adult and 7 pediatric patients. Successful isolation and culture was achieved for 95 samples (84.1 %) derived from five different regions of the heart: right and left ventricles, atrium, intraventricular septum, and apex. The average percentage of c-Kit⁺ cells, as assessed by FACS, ranged between 0.7 and 0.9 %. In contrast to published data we do not observed statistically significant differences in the number of c-Kit⁺ cells between disease-specific groups, parts of the heart or sexes. Nevertheless, c-Kit⁺ cells were present in significant numbers (11–24 %) in samples derived from three explanted pediatric hearts. c-Kit⁺ cells were also positive for CD105 and a majority of them was positive for CD31 and CD34 (83.7 ± 8.6 and 75.7 ± 11.4 %, respectively). Immunohistochemical analysis of the heart tissue revealed that most cells possessing the c-Kit antigen were also positive for tryptase, a specific mast cell marker. However, flow cytometry analysis has shown cultured c-Kit⁺ cells to be negative for hematopoietic marker CD45 and mast cell marker CD33. Isolated c-Kit⁺ cells display mesenchymal stem cell features and are thought to differentiate into endothelial cells.

c-Kit identifies a subpopulation of mesenchymal stem cells in adipose tissue with higher telomerase expression and differentiation potential

The stromal vascular fraction (SVF) of adipose tissue is an easy to obtain source of adipose tissue-derived stem cells (ADSCs). We and others have achieved significant but suboptimal therapeutic effects with ADSCs in various settings, mainly due to low rates of differentiation into specific cell types and with the downside of undesired side effects as a consequence of the undifferentiated ADSCs. These data prompted us to find new stem cell-specific markers for ADSCs and/or subpopulations with higher differentiation potential to specific lineages. We found a subpopulation of human ADSCs, marked by c-Kit positiveness, resides in a perivascular location, and shows higher proliferative activity and self-renewal capacity, higher telomerase activity and expression, higher in vitro adipogenic efficiency, a higher capacity for the maintenance of cardiac progenitors, and higher pancreatogenic and hepatogenic efficiency independently of CD105 expression. Our data suggests that the isolation of ADSC subpopulations with anti-c-Kit antibodies allows for the selection of a more homogeneous subpopulation with increased cardioprotective properties and increased adipogenic and endodermal differentiation potential, providing a useful tool for specific therapies in regenerative medicine applications.

c-Kit immunoexpression delineates a putative endothelial progenitor cell population in developing human lungs

Expression of c-Kit and its ligand, stem cell factor (SCF), in developing human lung tissue was investigated by immunohistochemistry. Twenty-eight human fetal lungs [age range 13 to 38 gestational wk (GW)] and 12 postnatal lungs (age range 1-79 yr) were evaluated. We identified c-Kit(+) cells in the lung mesenchyme as early as 13 GW. These mesenchymal c-Kit(+) cells in the lung did not express mast cell tryptase or α-smooth muscle actin. However, these cells did express CD34, VEGFR2, and Tie-2, indicating their endothelial lineage. Three-dimensional reconstructions of confocal laser scanning images revealed that c-Kit(+) cells displayed a closed-end tube formation that did not contain hematopoietic cells. From the pseudoglandular phase to the canalicular phase, c-Kit(+) cells appeared to continuously proliferate, to connect with central pulmonary vessels, and finally, to develop the lung capillary plexus. The spatial distribution of c-Kit- and SCF-positive cells was also demonstrated, and these cells were shown to be in close association. Our results suggest that c-Kit expression in early fetal lungs marks a progenitor population that is restricted to endothelial lineage. This study also suggests the potential involvement of c-Kit signaling in lung vascular development.

CXCR4 inhibition ameliorates severe obliterative pulmonary hypertension and accumulation of C-kit⁺ cells in rats

Successful curative treatment of severe pulmonary arterial hypertension with luminal obliteration will require a thorough understanding of the mechanism underlying the development and progression of pulmonary vascular lesions. But the cells that obliterate the pulmonary arterial lumen in severe pulmonary arterial hypertension are incompletely characterized. The goal of our study was to evaluate whether inhibition of CXC chemokine receptor 4 will prevent the accumulation of c-kit⁺ cells and severe pulmonary arterial hypertension. We detected c-kit⁺⁻ cells expressing endothelial (von Willebrand Factor) or smooth muscle cell/myofibroblast (α-smooth muscle actin) markers in pulmonary arterial lesions of SU5416/chronic hypoxia rats. We found increased expression of CXC chemokine ligand 12 in the lung tissue of SU5416/chronic hypoxia rats. In our prevention study, AMD3100, an inhibitor of the CXC chemokine ligand 12 receptor, CXC chemokine receptor 4, only moderately decreased pulmonary arterial obliteration and pulmonary hypertension in SU5416/chronic hypoxia animals. AMD3100 treatment reduced the number of proliferating c-kit⁺ α-smooth muscle actin⁺ cells and pulmonary arterial muscularization and did not affect c-kit⁺ von Willebrand Factor⁺ cell numbers. Both c-kit⁺ cell types expressed CXC chemokine receptor 4. In conclusion, our data demonstrate that in the SU5416/chronic hypoxia model of severe pulmonary hypertension, the CXC chemokine receptor 4-expressing c-kit⁺ α-smooth muscle actin⁺ cells contribute to pulmonary arterial muscularization. In contrast, vascular lumen obliteration by c-kit⁺ von Willebrand Factor⁺ cells is largely independent of CXC chemokine receptor 4.

Circulating and tissue resident endothelial progenitor cells

Progenitor cells for the endothelial lineage have been widely investigated for more than a decade, but continue to be controversial since no unique identifying marker has yet been identified. This review will begin with a discussion of the basic tenets originally proposed for proof that a cell displays properties of an endothelial progenitor cell. We then provide an overview of the methods for putative endothelial progenitor cell derivation, expansion, and enumeration. This discussion includes consideration of cells that are present in the circulation as well as cells resident in the vascular endothelial intima. Finally, we provide some suggested changes in nomenclature that would greatly clarify and demystify the cellular elements involved in vascular repair.

A single-arm phase II Austrian/German multicenter trial on continuous daily sunitinib in primary glioblastoma at first recurrence (SURGE 01-07)

BACKGROUND

Due to the redundancy of molecular pathways simultaneously involved in glioblastoma growth and angiogenesis, therapeutic approaches intervening at multiple levels seem particularly appealing.

METHODS

This prospective, multicenter, single-arm phase II trial was designed to evaluate the antitumor activity of sunitinib, an oral small-molecule inhibitor of several receptor tyrosine kinases, in patients with first recurrence of primary glioblastoma using a continuous once-daily dosing regimen. Patients received a starting dose of sunitinib 37.5 mg, followed by a maintenance dose between 12.5 mg and 50 mg depending on drug tolerability. The primary endpoint was a 6-month progression-free survival (PFS) rate. Secondary endpoints included median PFS, overall survival (OS), safety/toxicity, quality of life, and translational studies on the expression of sunitinib target molecules.

RESULTS

Forty participants were included in this study, and no objective responses were detected. PFS6 was 12.5%, median PFS 2.2 months, and median OS 9.2 months. Five participants (12.5%) showed prolonged stable disease ≥6 months with a median PFS of 16.0 months (range, 6.4-41.4 mo) and a median OS of 46.9 months (range, 21.2-49.2 mo) for this subgroup. c-KIT expression in vascular endothelial cells (n = 14 participants) was associated with improved PFS. The most common toxicities were fatigue/asthenia, mucositis/dermatitis, dysesthesias, gastrointestinal symptoms, cognitive impairment, leukoctopenia, and thrombocytopenia. Two participants (5%) terminated treatment due to toxicity.

CONCLUSION

Continuous daily sunitinib showed minimal antiglioblastoma activity and substantial toxicity when given at higher doses. High endothelial c-KIT expression may define a subgroup of patients who will benefit from sunitinib treatment by achieving prolonged PFS. ClinicalTrials.gov Identifier: NCT00535379.

Characterization of ion currents of murine CD117(pos) stem cells in vitro and their modulation under AT2 R stimulation

AIM

Hematopoietic stem cells, especially CD117(pos) cells, have been found to possess a regenerative potential in various tissues, in particular cardiac muscle. However, the characterization of the relevant ion currents of stem cells prior to implantation lacks documentation. Activation of angiotensin II type 2 receptor (AT2 R) can lead to further cell differentiation and receptor auto-expression and might thus influence electrophysiological properties of CD117(pos) stem cells. This study was designed to functionally characterize membrane currents of CD117(pos) cells under normal and AT2 R-stimulated conditions.

METHODS

CD117(pos) murine bone marrow stem cells were isolated with MACS technique and stimulated for the AT2 R with angiotensin II and losartan for 3-5 days prior to patch-clamp measurements. RT-PCR was used to determine channel expression. Endothelial properties were analysed with immunocytochemistry and acLDL uptake assay.

RESULTS

A well-expressed inward rectifying current (IKir ) was identified in cultured CD117(pos) cells. Furthermore, a ZD 7288 (HCN channel blocker)-sensitive current component was isolated. Voltage-dependent potassium currents and chloride currents were less expressed. A small fraction of cells demonstrated voltage- and time-dependent inward currents. In AT2 R-stimulated cells inward rectifying the hyperpolarization-induced inward currents were slightly attenuated on the translational level but showed increased mRNA expression. Cultured CD117(pos) cells express CD31 and VEGFR-2 and significantly increased the uptake of acLDL.

CONCLUSIONS

CD117(pos) cells do not have properties of action potential-generating cells and moderately change their excitability during AT2 R stimulation. Electrophysiological and molecular properties of control and AT2 R-stimulated cells point to a differentiation to vascular endothelial cells. This could increase beneficial vascularization in injured tissues.

Concise review: endothelial stem and progenitor cells and their habitats

Recent studies on the stem cell origins of regenerating tissues have provided solid evidence in support of the role of the resident cells, rather than bone marrow-derived or transplanted stem cells, in restoring tissue architecture after an injury. This is also true for endothelial stem and progenitor cells: local pools exist in the vascular wall, and those cells are the primary drivers of vascular regeneration. This paradigm shift offers an opportunity to rethink and refine our understanding of the multiple therapeutic effects of transplanted endothelial progenitor cells, focusing on their secretome, sheddome, intercellular communicational routes, and other potential ways to rejuvenate and replenish the pool of resident cells. The dynamics of vascular wall resident cells, at least in the adipose tissue, may shed light on the origins of other cells present in the vascular wall-pericytes and mesenchymal stem cells. The fate of these cells in aging and disease awaits elucidation.

Intra-abdominal fat depots represent distinct immunomodulatory microenvironments: a murine model

White adipose tissue (WAT) is a multi-faceted endocrine organ involved in energy storage, metabolism, immune function and disease pathogenesis. In contrast to subcutaneous fat, visceral fat (V-WAT) has been associated with numerous diseases and metabolic disorders, indicating specific functions related to anatomical location. Although visceral depots are often used interchangeably in V-WAT-associated disease studies, there has been a recent subdivision of V-WAT into "true visceral" and non-visceral intra-abdominal compartments. These were associated with distinct physiological roles, illustrating a need for depot-specific information. Here, we use FACS analysis to comparatively characterize the leukocyte and progenitor populations in the stromal vascular fraction (SVF) of peritoneal serous fluid (PSF), parametrial (pmWAT), retroperitoneal (rpWAT), and omental (omWAT) adipose tissue from seven-month old C57BL/6 female mice. We found significant differences in SVF composition between all four microenvironments. PSF SVF was comprised almost entirely of CD45(+) leukocytes (>99%), while omWAT contained less, but still almost two-fold more leukocytes than pmWAT and rpWAT (75%, 38% and 38% respectively; p<0.01). PmWAT was composed primarily of macrophages, whereas rpWAT more closely resembled omWAT, denoted by high levels of B1 B-cell and monocyte populations. Further, omWAT harbored significantly higher proportions of T-cells than the other tissues, consistent with its role as a secondary lymphoid organ. These SVF changes were also reflected in the gene expression profiles of the respective tissues. Thus, intra-abdominal fat pads represent independent immunomodulatory microenvironments and should be evaluated as distinct entities with unique contributions to physiological and pathological processes.

Restitutio ad integrum: a dream or a real possibility?

The subject of organ regeneration has attracted substantial investigative attention and has been extensively reviewed. Therefore, I shall focus on several only recently emerged issues and on those aspects of stem cell-mediated regeneration which, although are important in my opinion, have nevertheless evaded the radar of scientific pursuit. Specifically, I shall describe the recent work on the prominence of local lineage-restricted stem cells, as opposed to the bone marrow-derived or circulating ones, in regeneration. This will be followed by an attempt to re-interpret a bulk of published data on the beneficial effects of cell therapy with the focus on the secretome of stem cells. Multiple factors that conspire to cause insufficient or failed regeneration in adult mammals will be screened with emphasis placed on the mechanical forces, senescence and exhaustion, each leading to phenotypical switch and/or stem cell incompetence. Finally, I shall enumerate several potential pathways to induce or restore stem cell competence. Although a significant amount of work has been performed in the non-renal field, I would hope that some of the mechanisms and concepts discussed herein will eventually trickle into kidney regeneration.

Mouse models for studying angiogenesis and lymphangiogenesis in cancer

The formation of new blood vessels (angiogenesis) is required for the growth of most tumors. The tumor microenvironment also induces lymphangiogenic factors that promote metastatic spread. Anti-angiogenic therapy targets the mechanisms behind the growth of the tumor vasculature. During the past two decades, several strategies targeting blood and lymphatic vessels in tumors have been developed. The blocking of vascular endothelial growth factor (VEGF)/VEGF receptor-2 (VEGFR-2) signaling has proven effective for inhibition of tumor angiogenesis and growth, and inhibitors of VEGF-C/VEGFR-3 involved in lymphangiogenesis have recently entered clinical trials. However, thus far anti-angiogenic treatments have been less effective in humans than predicted on the basis of pre-clinical tests in mice. Intrinsic and induced resistance against anti-angiogenesis occurs in patients, and thus far the clinical benefit of the treatments has been limited to modest improvements in overall survival in selected tumor types. Our current knowledge of tumor angiogenesis is based mainly on experiments performed in tumor-transplanted mice, and it has become evident that these models are not representative of human cancer. For an improved understanding, angiogenesis research needs models that better recapitulate the multistep tumorigenesis of human cancers, from the initial genetic insults in single cells to malignant progression in a proper tissue environment. To improve anti-angiogenic therapies in cancer patients, it is necessary to identify additional molecular targets important for tumor angiogenesis, and to get mechanistic insight into their interactions for eventual combinatorial targeting. The recent development of techniques for manipulating the mammalian genome in a precise and predictable manner has opened up new possibilities for the generation of more reliable models of human cancer that are essential for the testing of new therapeutic strategies. In addition, new imaging modalities that permit visualization of the entire mouse tumor vasculature down to the resolution of single capillaries have been developed in pre-clinical models and will likely benefit clinical imaging.

Vascular repair and regeneration as a therapeutic target for pulmonary arterial hypertension

The last decade has seen substantial changes in our understanding of the pathobiology of pulmonary arterial hypertension (PAH), a severe and devastating disease without curative treatment. It is now accepted that injury to the endothelial cells of the pulmonary arteries is central for the subsequent development of lumen-obliterative lung vascular lesions. A variety of circulating and lung-resident progenitor and stem cells likely contribute to vascular integrity, and evidence for the presence of cells expressing stem and progenitor cell markers is found inside and in the immediate vicinity of pulmonary vascular lesions in PAH. The currently available vasodilator therapies mainly target enhanced vasoconstriction in the lung circulation and help to maintain or improve right ventricular function, but do not treat pulmonary vascular remodeling, the underlying cause of the disease. Vascular gene therapy and cell therapy with progenitor and stem cells is a progressing field in the context of the development of novel treatment options for PAH, but the majority of the studies are currently performed at the level of preclinical studies in animal models. The current review provides an overview of the current knowledge on cell- and gene therapy-based approaches for vascular repair and regeneration in PAH.