Abstract 18036: Exosomes From Human CD34+ Cells Mediate Angiogenic Effects in vitro and in vivo
In preclinical studies and early phase clinical trials, CD34+ cells have been shown to induce neovascularization in ischemic tissue, improving perfusion and function. Several reports have suggested that paracrine factors are responsible for some or all of the angiogenic effects induced by CD34+ cell transplantation. We hypothesized that human adult CD34+ cells mediate at least a part of their therapeutic function by secreting exosomes (Exo).
Methods and Results: We isolated Exo from the conditioned media of G-CSF mobilized adult human peripheral blood (PB) CD34+ cells and compared their angiogenic potency with intact CD34+ cells. PB mononuclear cells (MNC) and MNC Exo were used as controls. Exo purified from both CD34+ cells and MNC were shown to be a homogenous population 30–100nm diameter, have defined cup shaped morphology, and contain known Exo-specific proteins such as TSG101 and CD63 surface marker as shown by electron microscopy, Western blot and flow cytometry. The total amount of protein secreted in CD34+ Exo was 5-fold higher than the total protein in CD34+ cells, and about 50% higher than the MNC Exo. CD34+ Exo carry CD34 lineage markers including CD34 protein and CD34 mRNA. Compared to CD34+ cells, CD34+ Exo significantly increase the proliferation of human umbilical-vein endothelial cells (HUVECs) (32±8 % v 43±8%, p<0.01), and significantly induce tube formation of HUVECs (13±8 v 43±9 tubes, p<0.001) in in vitro Matrigel tube formation assay. Furthermore, the tube formation induced by CD34+ Exo was dose-dependent and similar to angiogenic effect of 100X number of intact CD34+ cells. MNC Exo did not induce tube formation. In-vivo, neovascularization and incorporation of mouse endothelial (CD31+) cells were significantly higher with CD34+ Exo than with CD34+ cells (7±1.5 % v 2±0.4%, p<0.1) as shown by Matrigel-plug assay.
Conclusions: These data indicate that CD34+ Exo induce angiogenic activity in the absence of CD34+ cells, which suggest the Exo as important mediators of the angiogenic effects associated with CD34+ cell therapy. This hypothesis is currently being tested in in vivo ischemic models. We speculate that Exo derived from CD34+ cells may represent a suitable replacement to progenitor-cell transplantation for therapeutic angiogenesis.
- © 2010 by American Heart Association, Inc.