Abstract-Pulmonary arterial hypertension (PAH) is characterized by a progressive increase in pulmonary vascularresistance caused by narrowing and loss of pulmonary microvasculature, which in its late stages becomes refractory to traditional therapies. We hypothesized that bone marrow-derived endothelial progenitor cells (EPCs), which normally function to repair and regenerate blood vessels, would restore pulmonary hemodynamics and increase microvascular perfusion in the rat monocrotaline (MCT) model of PAH. Mononuclear cells were isolated from the bone marrow of syngeneic Fisher-344 rats by Ficoll gradient centrifugation and cultured for 7 to 10 days in endothelial growth medium. Fluorescently labeled endothelial-like progenitor cells (ELPCs) engrafted at the level of the distal pulmonary arterioles and incorporated into the endothelial lining in the MCT-injured lung. The administration of ELPCs 3 days after MCT nearly completely prevented the increase in right ventricular systolic pressure seen at 3 weeks with MCT alone (31.5Ϯ0.95 versus 48Ϯ3 mm Hg, respectively; PϽ0.001), whereas injection of skin fibroblasts had no protective effect (50.9Ϯ5.4 mm Hg). Delayed administration of progenitor cells 3 weeks after MCT prevented the further progression of PAH 2 weeks later (ie, 5 weeks after MCT), whereas only animals receiving ELPCs transduced with human endothelial NO-synthase (eNOS) exhibited significant reversal of established disease at day 35 (31Ϯ2 mm Hg, PϽ0.005) compared with day 21 (50Ϯ3 mm Hg). Fluorescent microangiography revealed widespread occlusion of pulmonary precapillary arterioles 3 weeks after MCT, whereas arteriolar-capillary continuity and microvascular architecture was preserved with the administration of syngeneic ELPCs. Moreover, the delivery of ELPCs to rats with established PAH resulted in marked improvement in survival, which was greatest in the group receiving eNOS-transduced cells. We conclude that bone marrow-derived ELPCs can engraft and repair the MCT-damaged lung, restoring microvasculature structure and function. Therefore, the regeneration of lung vascular endothelium by injection of progenitor cells may represent a novel treatment paradigm for patients with PAH. ( Key Words: progenitor cells Ⅲ pulmonary hypertension Ⅲ endothelium Ⅲ endothelial nitric oxide synthase P ulmonary arterial hypertension (PAH) is a devastating disease that in its most severe form, idiopathic PAH, leads to progressive debilitation and death, often within 2 to 3 years after its initial diagnosis. 1 Despite significant advances in the therapy of PAH during the last decade, the prognosis remains poor. Although the genetic basis for some patients with familial PAH has been elucidated, 2-4 how these mutations are causally linked to the development of PAH remains unclear. 5,6 Evidence from experimental models as well as lung specimens from patients with PAH underlines the importance of microvascular occlusion in the pathogenesis of this disease, 7 especially in its advanced stages; however, the precise mechanisms...

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We present a novel animal model for post-transplant obliterative airway disease in which the donor trachea is implanted into the recipient's lung parenchyma. Although this procedure is technically more challenging than the heterotopic model of implantation into a subcutaneous pouch, it has several important advantages some of which are the appropriate local environment and the possibility of local immunosuppressive therapy after transtracheal gene, cell or drug delivery. This model has revealed new insights into angiogenic potential of the pulmonary circulation.