CXCR4 and pulmonary arterial hypertension: Functional studies using late-outgrowth progenitor cells from familial PAH patients (with BMPR2 gene mutations) demonstrated the presence of hyperproliferative endothelial phenotype (CD45+/CD133+/c-kit+/CXCR4+) in remodeled pulmonary arteries, occlusive and plexiform lesions, with impaired ability to form vascular networks and altered BMPR2 pathway [18].