Blocking SDF-1α activity inhibits BM contribution to tumor neovascularization. After LLC inoculation, mice were treated with intratumoral anti–SDF-1α antibodies to block BM contribution (n = 5). (A-B) Tumors treated with anti–SDF-1α contained significantly lower numbers of BM-derived cells throughout the tumor mass seen visually (A; scale bars represent 100 μm) and by counting GFP⁺ cell numbers in standardized field sizes (B; *P < .05). (C-D) Treated mice also had significantly fewer cells integrated within blood vessel walls (C) and decreased MVD (D) compared with control tumors (*P < .05). (E) Animals treated with anti–SDF-1α antibodies (♦) also generated significantly smaller tumors in comparison with controls (●; *P < .05). (F) The growth kinetics of LLCs in culture with various doses of anti–SDF-1α antibodies (0 to 50 μg/mL) were similar over the range of concentrations tested. No cytotoxicity was observed at 0 (○), 12.5 (□), 25 (▵), and 50 μg/mL (x) of the anti–SDF-1α antibodies in growth media (n = 4).