Treatment of tumor-bearing mice with L19–IL-2 or D1.3–IL-2 fusion proteins.

(A) Upper part: treatment schedule of mice. Treatment began 72 hours after F9 murine teratocarcinoma implantation in syngeneic mice; mice received daily intravenous injections of 12 μg L19–IL-2 or D1.3–IL-2 corresponding to 72 000 IU, or saline for 6 consecutive days. Animals were killed on the 10th day. The photograph shows the F9 tumors dissected from the different groups of animals. (B) Immunohistochemistry using a rat antimouse CD 45R/B220 antibody of the F9 tumor from a mouse treated with D1.3–IL-2 (i) and from a mouse treated with L19-IL-2 (ii). Scale bar indicates 30 μm.