Antitumor effects of antibody-diphtheria toxin conjugates. II. Immunotherapy with conjugates directed against tumor antigens induced by simian virus 40.

Hamster and rabbit antibodies against antigens on the surface of simian virus 40 (SV40)-transformed hamster sarcoma or lymphoma cells were purified by immunoadsorption on SV40-transformed cells and conjugated to diphtheria toxin with glutaraldehyde. Treatment with a single dose of antibody-toxin conjugate partially protected hamsters concurrently challenged with 10(3) SV40-transformed sarcoma cells, as evidenced by a reduction in tumor incidence, an increase in tumor latency, and a prolongation of the life-spans of hamsters that developed tumors. Treatment of established sarcomas was ineffective, but repeated treatment with the conjugates induced complete regressions in 20-56% of hamsters bearing established transplants in the SV40-induced lymphoma.