Abstract
Crude 3m KCI extracts of the chemically induced C3H/ HeJ fibrosarcomas, MCA‐F and MCA‐D, possess two immunobiologically active components upon fractionation by preparative isoelectric focusing. Strongly acidic (pl 2.5‐3.6) antigens induced potent tumor facilitation while mildly acidic (pl 5.8‐6.0) proteins engendered resistance to neoplastic cell challenge. The possibility that these proteins were tumor‐specific transplantation antigens (TSTA) was investigated in specificity tests using fractions prepared from the MCA‐F and MCA‐D. Pre‐treatment of individual groups of mice with the tumor‐facilitating and immunizing fractions from extracts of two antigenically different fibrosarcomas MCA‐F and MCA‐D followed 10 days later by challenge of all groups with both neoplasms revealed both responses to be specific for the tumor of origin. The immunizing fractions from MCA‐F and MCA‐D engendered 50% (p<0.01) and 60% (p<0.01) reduction in the growth of their respective tumor cell challenge. Facilitating antigens of both tumors specifically potentiated only the growth of their parent neoplasms by more than 75% (p<0.01). Non‐specific protection was not observed, demonstrating that both fractions bore TSTA activity. Both the resistant state and the condition of facilitated tumor growth engendered by the isolated tumor cell fractions could be adoptively transferred to normal syngeneic recipients via lymphoid cells, and the im‐munoprotective fraction evoked specific delayed‐type hypersensitivity in immunized hosts. Assessment of the activity of the partially purified TSTA revealed that the immunizing fraction of MCA‐F exhibited narrow range dose‐response properties. Immunoprotection was demonstrable within a restricted range whether the antigen was administered as whole cells, crude extract, or pIEF purified material. These results indicate that (1) separate tumor‐facilitating and immunizing activities are common features of carcinogen‐induced tumors; (2) the antigen‐induced facilitation of, and resistance to, tumor cell challenge is mediated by lymphoid cells; (3) both moieties display distinct antigenic specificity in vivo; and (4) the restricted range of immunoprotection is a property intrinsic to at least some carcinogen‐induced tumors and their antigenic subcellular fractions.