Immunologic enhancement of B16 melanoma growth

In certain experimental tumor models, tumor growth is less pronounced in immune deficient animals. Characteristically, tumors such as the murine B16 melanoma and Lewis lung carcinoma (3LL) are weakly antigenic. We proposed that with such tumors that are weakly antigenic, growth is enhanced by T-cell factors. Young mice were inoculated with irradiated B16 cells in complete Freunds adjuvant (CFA) on three occasions, each separated by 2 weeks. Specific antibody (IgG) to B16 membrane antigens was detected by an enzyme-linked immunosorbent assay (ELISA) after the first injection, and it continued to rise for 6 weeks. B16 growth was compared in 20 mice that had received irradiated B16 in CFA or CFA alone by the same schedule previously. Despite the previous sensitization, the rates of tumor appearance and growth were similar. In an additional experiment involving 23 mice that had received B16 immunization, the period of time in which a palpable tumor developed after the injection of viable B16 cells did not correlate with anti-B16 antibody level. It appeared that detectable antibody to B16 antigens was of little consequence. To explain why B16 primary growth and metastases were reduced in immune deficient hosts, we proposed that lymphocytes might enhance tumor growth. To demonstrate this, splenic lymphocytes from tumor-bearing (B16 or 3LL) or control mice were injected with B16 cells into young, immune competent hosts. Tumors (B16) developed earlier and growth was more rapid in mice that received spleen cells from tumor-bearing (B16) mice. Subsequent cell depletion experiments to determine the mediator of tumor enhancement implicated a T-cell fraction that was neither of T-helper nor T-suppressor cell type phenotypically. Immune deficiency states that are associated with dysfunction of those cells that account for tumor enhancement might explain the reduced tumor aggressiveness that is observed frequently in these conditions.