Immunogenicity and amplifier cell production by tumor vaccines enhanced by concanavalin A

The induction of immune resistance to L1210 murine leukemia by 3 types of L1210 vaccines was compared under conditions in which in vitro cell proliferation and transplantability to mice were completely suppressed. L1210 cells treated with glutaraldehyde plus concanavalin A (ConA) were more potent in inducing antitumor immunity than those treated with Vibrio cholerae neuraminidase or mitomycin C (MMC). This and the finding that cell-bound ConA enhanced the immunogenic potency of MMC- or formaldehyde-treated L1210 vaccines indicate that ConA endowed the cells with additional potency in inducing antitumor immunity. ConA-free and ConA-bound vaccine cells took up the same amount of anti-L1210 antibody, suggesting that cell-bound ConA did not increase tumor-associated antigen molecules on the tumor cell surface. However, adoptively transferred spleen cells of mice sensitized with ConA-bound, but not ConA-free, vaccine amplified the vaccine-induced antitumor immunity in the recipients. These donor spleen cells suppressed the in vitro proliferation of live L1210 cells no more than non-primed spleen cells, nor was their amplifying activity abrogated by treatment with anti-Lyt-2.1 antibody and rabbit sera as a source of complement. This indicated that cytotoxic T cells and/or their precursors were not involved in the observed amplification. This as well as the finding that their amplifying activity was completely abrogated by treatment with rabbit anti-mouse brain-associated T cell antigen antisera and rabbit sera as a source of complement, led us to conclude that amplifier T cell production, associated with vaccine-bound ConA, was responsible for the enhanced immunogenic potency of ConA-bound vaccines.