Circulating human hematopoietic stemcells, identified by their CD34 antigenicity, have been shown to contribute to peripheral vasculogenesis as evidenced by their incorporation into actively growing vessels of experimentally induced ischemic hind limbs. The purpose of the present studywas to test whether CD34+ cells migrate, differentiate and assemble into new vessels at sites of myocardial injury. Hearts of 17 athymic mice were injured by multiple transmyocardial punctures with a 25g needle; 2 athymic mice underwent shamoperations. Two days later, themain experimental group of 8 mice received an intravenous injection (via the tail vein) of approximately 2×105 CD34+ cells
isolated from normal human donors which were labeled with the fluorescent dye DiI. The other mice were divided into 4 other groupswhich served as controls. These consisted of 2 shamoperated mice followed by DiI labeled CD34+ cell injections, 2 mice with myocardial injuries without any cell injections, 5 mice with myocardial injury plus injection ofDiI labeled peripheral mononuclear cells after extraction of CD34+ cells and 2 mice with myocardial injury followed by intravenous injection of DiI (no cells). Mice were sacrificed 14 days later and histologic analysis, including
immunostaining and in situ hybridization, was performed. DiI fluorescence was identified exclusively in the injured regions of the hearts.Within these regions, capillaries and larger vessels were identified which were lined with elongated, flattened DiI+ cells; in many instances these vessels were completely composed of the DiI+ cells. Co-localization ofDiI fluorescence and factor VIII, CD31 and HLA1 confirmed that these were the injected human cells which had been incorporated into, or perhaps formed, vascular structures. A large number ofDiI+ cells localized to the interstitial areas of the injury also stained positive for factor VIII, CD31 and eNOS gene expression even though they did not incorporate into vessels nor take on the appearance of endothelial cells. Lung, kidney, liver and spleen of all animals and hearts of shamoperated animals were devoid ofDiI+ fluorescence. Thus, exogenous endothelial progenitor cells migrate to injured myocardium. Complete vessels can be formed de novo in the heart from these cells (true
vasculogenesis). The use of exogenous progenitor cells may provide be useful as one component of strategies to form new vessels in the hearts of patients with severe coronary artery disease.
Tags: Cell Therapy, stem cell