Effect of horse antibody to rat alpha‐fetoprotein upon the growth of AH‐66 in donryu rats

Studies were undertaken to evaluate whether the intraperitoneal administration of horse antibody to rat alpha‐fetoprotein (HabRatAFP) would inhibit or prevent the growth of AH‐66 tumor cells inoculated into Donryu male rats. In animals inoculated with tumor subcutaneously there was 100% tumor growth in uninjected control animals and the administration of HabRatAFP prevented tumor growth in 7/24 (29%) of the animals. When animals were inoculated with tumor intraperitoneally, the inhibition of tumor growth by Hab‐RatAFP only occurred at tumor‐cell doses of 50,000, 10,000, and 5,000. In these three groups, 15/35 (43%) of those animals treated with Hab‐RatAFP did not develop tumor whereas 1/36 (3%) of the normal horse‐serum treated animals did not develop tumor. The majority of those animals which were cured of their tumors by Hab RatAFP treatment resisted tumor rechallenge. Studies were done to elucidate the mechanisms responsible for the anti‐tumor effect of HabRatAFP. AH‐66 tumor cells which were placed into millipore chambers, implanted intraperitoneally, were killed by the intraperitoneal administration of HabRatAFP. Studies were conducted to see if treatment with HabRatAFP to rat AFP might increase the immunogenicity of an inoculum of X‐irradiated tumor cells. In one experiment, no animals which received only X‐irradiated tumor cells resisted tumor rechallenge with 5 × 106 tumor cells whereas 6/11 (54.5%) of those animals which received X‐irradiated tumor cells and treatment with HabRatAFP resisted tumor rechallenge.