In vivo potentiation of concanavalin A-bound L1210 vaccine by antimacrophage agents.

Carrageenan potentiated in vivo the primary and secondary responses by concanavalin A (Con A)-bound L1210 murine leukemia vaccine and induced in histocompatible animals enhanced immune resistance to subsequent inoculations of live L1210 cells. This enhancement was critically dependent on the vaccine preparation and the administration timing of carrageenan. Carrageenan potentiated Con A-free vaccine to a much lesser extent if at all, than did Con A-bound vaccine, and it was effective only on the day of or one day after vaccine administration. This enhancement was L1210 specific as evidenced by the lethal growth of P388 leukemia cells in animals inoculated with Con A-bound L1210 vaccine and carrageenan. This is explicable by the increase of spleen but not peritoneal exudate effector cells as measured by suppression of in vitro L1210 cell growth. The following findings suggested that potentiation of Con A-bound vaccine by carrageenan was achieved by affecting suppressor macrophages. Silica and trypan blue, other antimacrophage agents, potentiated Con A-bound vaccine. The enhancement was nullified by the macrophage-stabilizing agent, poly-2-vinylpyridine N-oxide. This hypothesis was further evidenced by the following findings. Phagocytic peritoneal cells induced by Con A-bound vaccine and adhering to the plastic vessel suppressed in vitro spleen cell blastogenesis. Antimacrophage agents abrogated not only production but also activity of these suppressor cells. The combined administration of Con A-bound L1210 vaccine and carrageenan produced an enhanced antitumor immune response and prolonged the life span of tumor-bearing animals marginally but significantly.