The effect of a
muramyl dipeptide derivative (B30-MDP) on the augmentation of antitumour immunity against highly metastatic L5178Y-ML25 mouse
lymphoma cells was examined in CDF1 (Balb/c x DBA/2) mice. Mice immunized with a mixture of X-irradiated tumour cells (10(3)) and
B30-MDP (100 micrograms) on 7 days prior to challenge by viable tumour cells displayed a significant decrease in
metastasis towards the target organs, liver and spleen, compared with that of untreated mice. Immunization of mice with the mixture on day 5 or 7 after tumour challenge, when the level of
glutamic-pyruvic transaminase (GPT) and
glutamic-oxaloacetic transaminase (GOT) in sera of mice inoculated with viable tumour cells was observed to be normal, caused less
metastasis than immunization with X-irradiated tumour cells alone. Sensitization with X-irradiated tumour cells admixed with
B30-MDP induced almost two times higher cytotoxicity of spleen cells against L5178Y-ML25
lymphoma cells than sensitization with X-irradiated tumour cells without
B30-MDP. In contrast, cytotoxic activity of spleen cells against another target, L1210
lymphoma cells derived from BDF1 mice, was not observed by immunization with X-irradiated L5178Y-ML25 cells with or without
B30-MDP. Specific lysis by splenic cells of the immunized mice against L5178Y-ML25 cells decreased to the normal level when T cells were deleted from the immunized spleen cells by the treatment of rabbit anti-mouse Thy1.2 antibody and rabbit
complement. These results indicate that
B30-MDP is able to augment a specific tumour immunity due to the enhancement of cytotoxicity mediated by T lymphocytes, and is useful as an immunopotentiating agent for active immunization of inactivated tumour cells.