Administration of VE-cadherin antibody abrogates the effect of EPC infusions on hematopoietic recovery. PB WBCs, neutrophil counts, and platelet counts were measured over time in BALB/c mice that were irradiated with 550 cGy TBI and then treated systemically with either EPCs alone, EPCs plus VE-cadherin antibody, VE-cadherin antibody alone, or PBS as described in “Methods.” VE-cadherin treatments are represented by red arrows. (A) Comparison in WBC (Ai), neutrophils (Aii), and platelet count (Aiii) recovery in mice treated with EPCs alone versus mice treated with EPCs plus VE-cadherin treatments. Mice that were treated with EPCs plus VE-cadherin antibody (gray line) demonstrated significantly delayed recovery of WBCs and platelets compared with mice treated with EPCs alone (blue line). *P < .001 and P = .006 for differences in WBCs at days 14 and 17 (Ai). Platelet recovery was significantly delayed in mice treated with EPCs plus VE-cadherin versus mice treated with EPCs alone (Aiii). *P = .01, P = .002, and P < .001 for differences in platelet counts at days 14, 17, and 21. (B) Treatment with VE-cadherin antibody alone (red line) delayed WBC, neutrophil, and platelet recovery in irradiated mice compared with irradiated control mice (black line). *P = .003 and P = .002 for differences in WBCs at days 14 and 17 (Bi WBCs). *P = .002 and P = .007 for differences in neutrophil counts between VE-cadherin antibody–treated mice and controls at days 14 and 17 (Bii Neutrophils). *P = .03, P < .001, and P = .01 for differences in platelet counts between VE-cadherin antibody–treated mice and controls at days 14, 17, and 21. ∧P = .01 for increase in platelet count in VE-cadherin antibody–treated mice versus controls at day 10 (Biii Platelets). Data points represent the means plus or minus SEM of n = 10 to 15 mice per time point.