Multiple injections of 3 m KCI extracts of SV40-induced hamster sarcoma cells were found to have no inhibitory effect on tumor growth in syngeneic hamsters following homologous tumor challenge. When a single injection of the same extract was administered in the range of 0.5 mg of antigen protein, a significant delay in the appearance of tumors was repeatedly observed, and a significant number of challenged animals failed to develop tumors in two of three experiments. Subsequent studies established that a single injection of the tumor cell extract generally conferred 20 to 40% permanent protection, always with a marked delay in tumor appearance. The immunity was specific in that neither immunization with normal muscle extracts nor heterologous tumor challenge resulted in protection or delay in tumor appearance. Higher or lower amounts of homologous, soluble tumor transplantation antigen given in a single injection were either without effect or promoted tumor development. The resistance observed in animals receiving a single dose of soluble tumor antigen could only be detected if the hamsters were challenged with 5 × 105 tumor cells. Challenge with only 104 tumor cells did not lead to the detection of resistance. The immunity induced by a single optimal dose of tumor antigen could be transferred to normal, uninjected hamsters at 20 days postsensitization with lymph node cells but not with peritoneal exudate cells from injected donors, suggesting that the immunity detected in animals immunized with soluble tumor extracts was cell mediated. Taken together, these data indicate that antigen dose, regimen of administration to the host, and the challenge level used to detect transplantation resistance are all important parameters to detect transplantation resistance are all important parameters to consider when using cell-free, tumor-associated transplantation antigens. These data strongly support and extend an earlier related report derived in another model with a chemically induced tumor.

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This research was supported by NIH Grant CA2 2674 from the National Cancer Institute, and by Department of Energy, Contract EE 77S05-5601.

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