[The synergistic action of lipopolysaccharide and muramyl dipeptide in the immunotherapy of DBA/2 mice with mastocytoma P815].

The intratumoral administration of lipopolysaccharide (LPS) and muramyl dipeptide (MDP) in combination, but not separately, resulted in necrosis and rejection of subcutaneous P815 mastocytoma nodules in DBA/2 mice with 30 to 40% survival. Previous sensibilization of animals by LPS + MDP, treatment by indomethacin, cyclophosphamide or syngeneic lymphocytes did not augment the immunotherapeutic action of LPS + MDP combination. Reinoculation of P815 cells into cured DBA/2 mice 8 months after the disappearance of the primary tumor led to rejection of new nodules with 50% survival rate. In LPS + MDP immunotherapy of these tumors two stages may be distinguished by a thrombo-necrotic stage and that of development of immunity.