Pooled F(ab')2 fragments of three MAbs against distinct
epitopes of
carcinoembryonic antigen (CEA) were used for
radioimmunotherapy of nude mice bearing a subcutaneous human colon
carcinoma xenograft. 9-10 d after
transplantation when
tumor nodules were in exponential growth, 36 mice were treated by
intravenous injection of different amounts of 131I-labeled MAb F(ab')2. All 14 mice injected with a single dose of 2,200 (n = 10) or 2,800 microCi (n = 4) showed complete
tumor remission. 8 of the 10 mice treated with 2,200 microCi survived in good health for 1 yr when they were killed and shown to be
tumor free. Four of nine other mice treated with four fractionated doses of 400 microCi showed no
tumor relapse for more than 9 mo. In contrast, all 15 mice injected with 1,600-3,000 microCi 131I-control
IgG F(ab')2 showed
tumor growth retardation of only 1-4 wk, and 15 of 16 mice injected with unlabeled anti-CEA MAb F(ab')2 showed unmodified
tumor progression as compared with untreated mice. From tissue radioactivity distributions it was calculated that by an injection of 2,200 microCi 131I-MAb F(ab')2 a mean dose of 8,335 rad was selectively delivered to the
tumor, while the tissue-absorbed radiation doses for the normal organs were: peripheral blood, 2,093; stomach, 1,668; kidney, 1,289; lung, 1,185; liver, 617; spleen, 501; small intestine, 427; large intestine, 367; bone, 337; and muscle, 198. These treatments were well tolerated since out of 19 mice with complete
tumor remission only 4 required
bone marrow transplantation and 17 were in good health for 6-12 mo of observation. The results demonstrate the selective destruction of established human colon
carcinoma transplants by
intravenous injection of either single or fractionated doses of 131I-MAb F(ab')2.