Specific tumor immunity induced with soluble materials: restricted range of antigen dose and of challenge tumor load for immunoprotection.

Immunogenic materials were solubilized from two methylcholanthrene-induced fibrosarcomas using 3 M KCl and were assessed for antigen activity in an immunoprotection assay. Mice which had been pretreated with a single injection of extract (0.1 to 2.0 mg protein) were challenged 10 days later with 10(3), 10(4), or 10(5) tumor cells. Optimal protection, as evidenced by survival, tumor incidence, and prolonged latent period before neoplastic outgrowth, was found after pretreatment with 0.5 mg of crude KCl extract and challenge with 10(4) tumor cells. These results further reinforce the weak nature of tumor-specific antigens as immunogens and show that only in very restricted circumstances can solubilized preparations administered without adjuvant induce immunoprotection in syngeneic hosts.