Distribution and pharmacokinetic of CD20-Flex BiFP. (A) The distribution of CD20-Flex BiFP. BALB/c mice bearing A20-CD20 tumors were intravenously injected with 0.1 mL (2×10⁶ counts per minute/mouse) of ¹²⁵I-labeled rituximab, Flex-Ig, or CD20-Flex BiFP. At 24 hours after injection, the animals were sacrificed and different tissue samples were collected and assayed for radioactivity. Data are presented as %ID/g of tissue and values are the mean ± SD derived from 3 organs of 3 different animals. (B) Groups of 8-week-old female Imprinting Control Region mice were injected with 10 mg/kg rituximab, Flex-Ig, or CD20-Flex BiFP via the tail vein. Antibody concentrations in plasma were determined. Each data point is the mean ± SD of the measurements of 3 samples from 3 different animals.