Umbilical Cord Blood CD133⁺ Stem Cells Exhibit Vasculogenic Capacity In Vitro and Augment Neovasculogenesis In Vivo in a Murine Model of Vascular Ischemia.

Recent reports have utilized a variety of cell types for cellular therapy in mediating therapeutic angiogenesis in response to ischemia. We sought to assess the vasculogeneic potential of selected CD133⁺ hematopoietic stem cells (HSC) from umbilical cord blood (UCB) utilizing in vitro functional assays and an in vivo murine hind-limb ischemia model.

Methods & Results: Mononuclear cells (MNC) from UCB or bone marrow (BM) were incubated with CD133⁺ conjugated magnetic beads, followed by automated sorting through magnetic columns (Miltenyi). Routine yield of CD133⁺ cells was 0.5±0.2% of UCB MNC and 0.7±0.3% of BM MNC, with a purity of 79±2% (UCB, n=30) and 84±5% (BM, n=12). Surface expression in the UCB CD133⁺ population was 3.6±1.5% KDR(VEGFR2), 8.7± 3.8% CXCR4 and 22.7±2.8% CD105 compared to 9.2±1.8% KDR, 14.4±1.3% CXCR4 and 23.7±2.3% CD105 in the BM CD133⁺ population. We measured chemotactic migration of cells towards SDF-1 (100ng/mL) compared to control wells containing media alone. The fold increase over control was 4.9±2.9 UCB MNC, 1.8±0.7 UCB CD133⁺ and 8.3±1.7 BM CD133⁺ (n=3). Angiogenic protein assays of CD133⁺ cells demonstrated elevated levels of IL-8 production as compared to MNC (10³+/−380 pg/mL greater in CD133⁺ than MNC from the same UCB unit) when cultured for 24h in basal media. NOD/SCID mice underwent ligation of the right femoral artery and were given cells or vehicle control via intracardiac injection immediately following injury. Mice were given 1 x 10⁶ MNC or 0.5 x 10⁶ CD133⁺ cells. Laser Doppler flow measurements were obtained from both limbs each week for 6 weeks and the ratio of perfusion in the ischemic/healthy limb was calculated. At 28 days, perfusion ratios were statistically higher in study groups receiving UCB CD133⁺ cells, 0.55±0.06 (n=9), BM CD133⁺ cells 0.47±0.07 (n=8), BM MNC 0.48±0.8 (n=6) compared to cytokine controls 0.37±0.03 (n=12, p<0.05). Mice receiving UCB MNC did not show statistically significant improvement in measured blood flow over control animals 0.42±0.05 (n=8, p=0.34). At sacrifice, bone marrow was harvested to assess engraftment of human cells by flow cytometric analysis. Mice injected with UCB CD133⁺ cells showed 19±4.9% positive huCD45 cells compared to 2.5±0.6% for UCB MNC, 1.6±0.4% for BM CD133+ cells and 2.3±0.3% for BM MNC (n=3). Histological studies from day 42 tissue samples of muscle distal to arterial ligation were evaluated for capillary density. Control animals had capillary density of 131±6.9 cells/mm². Capillary density was statistically higher that controls in animals receiving UCB CD133⁺ (320±18; p<0.0001), BM CD133⁺+ (183±9.3; p<0.0001), and UCB MNC (164±10.5; p=0.011). Mice treated with BM MNC (135±9.4) did not have a statistically significant increase in capillary density from controls (p=0.73). In addition, animals treated with either UCB or BM-derived CD133⁺ cells had statistically higher capillary density than unselected MNC (p=<0.0001 and p=0.0004, respectively).

Conclusions: In vitro functional assays showed that UCB-derived CD133⁺ HSC demonstrate enhanced homing capability (migration) as well as the potential for cellular recruitment (via IL-8 production) for angiogenesis in response to ischemia. Furthermore, UCB derived CD133⁺ HSC mediate significantly improved blood flow in an in vivo murine hind-limb injury model of ischemia, indicating the greater vasculogenic potential of selected CD133⁺ cells from of this stem cell source.