Human CD34^– mononuclear cells also home to peripheral tumor vasculature. (A) Intravital microscopy of CMTMR-labeled CD34^– mononuclear cells homing to tumor vessels. Shown are peripheral and central tumor vascular beds as well as neighboring fat-pad at 20 minutes after injection in animals injected with CMTMR-labeled CD34^– mononuclear cells (arrowheads). Magnification, ×200. Tumor center and periphery at 72 hours after injection of cells are also shown. (B) Average number of CMTMR CD34^– cells in the tumor center, tumor periphery, and fat-pad per ×200 field ± SEM after 15 minutes. *P < 0.0009. (C) Postmortem tumor section shows CD34^– cells (red; arrows) at the GFP⁺ (green) tumor periphery (left). Magnification, ×400. Also shown are CD31⁺ blood vessels (red) at the GFP⁺ (green) tumor periphery (right). Magnification, ×200.