Non-cytotoxic activity of pyran copolymer-induced macrophages associated with potentiation of tumour vaccine in recipient mice.

Mice inoculated with both L1210 murine tumour vaccine and pyran copolymer were more resistant to L1210 than those inoculated with either of these agents alone. Rabbit anti-mouse thymocyte globulin and silica reduced the augmented resistance of these mice, suggesting the involvement of activated anti-tumour T cells and macrophages in the augmented resistance. We studied the activation of these two cells separately and examined the possible contribution of pyran copolymer-induced peritoneal cells to the augmented resistance to an inoculation of live tumour. Pyran copolymer-induced peritoneal cells endowed the tumour vaccine-primed mice, but not unprimed mice, with resistance to implanted L1210 and, among those peritoneal cell populations, macrophages but not T cells were responsible for this effect since the activity was associated with a cell population which was adherent to nylon wool columns, sensitive to silica and insensitive to anti-Thy 1.2 antibody plus complement. The pyran copolymer-induced peritoneal cells had very little antiproliferative activity when tested against L1210 in vitro and mice inoculated with these peritoneal cells did not survive a challenge of live L1210 cells much longer (less than 1 day) than L1210 inoculated control mice. Furthermore, the survival of L1210 vaccine-primed mice inoculated with one-tenth the amount of live L1210 (10(2)) was still much shorter than that of mice primed with L1210 vaccine plus pyran copolymer and challenged with ten times as many (10(3)) live L1210 cells. Therefore, direct tumoricidal activity was probably not a major factor in the in vivo immunological augmenting activity of the pyran copolymer-induced macrophages.