Distribution of mu-IgG1k anti-huCD20 (C2B8, ibritumomab-tiuxetan). (A) A group of 30 mice received 130 μCi radiolabeled ibritumomab and biodistribution was assessed by immunoscintigraphy. Amount of radioactivity was correlated with tumor burden (r2 = 0.97). (B) Radioactivity decreased with time for mice with high (> 3 × 106 AU) (●) and intermediate (from 0.15 × 106 to 3 × 106 AU) (△) tumor burden, whereas it increased for mice with low (< 0.15 × 106 AU) ( □ ) tumor burden. (C,D) To evaluate antibody tissue distribution, a group of mice (n = 20) received 400 μCi radiolabeled ibritumomab and were killed on day 1. Involved nodes identified and quantified by BLI were then collected, and radioactivity was evaluated on 3-μm cuts. The gray level code indicates range of radioactivity in lymph nodes from low (white) to high (black). The radioactive intensity was measured on a diameter and reported below. The smallest nodes showed a homogeneous antibody distribution, whereas no radioactivity was found in the middle of the biggest nodes. Blood vessels (*) and radioactivity were colocalized at the peripheral of the nodes. Results shown are representative of independent experiments.
