The augmentation of tumor-specific immunity using haptenic muramyl dipeptide (MDP) derivatives. II. Establishment of tumor-specific immunotherapy models utilizing MDP hapten-reactive helper T cell activity.

Preinduction of potent haptenic muramyl dipeptide (MDP)-reactive helper T cell activity and subsequent immunization with MDP hapten-coupled syngeneic tumor cells resulted in enhanced induction of tumor-specific immunity through T-T cell collaboration between anti-MDP hapten helper T cells and tumor-specific effector T cells. The present study establishes two types of tumor-specific immunotherapy protocols utilizing helper T cells against MDP hapten cross-reactive with Bacillus Calmette Guérin (BCG). In the first model, naive normal C3H/He mice or mice in which MDP hapten-reactive helper T cells had been generated by BCG-sensitization were inoculated i.d. with syngeneic X5563 tumor cells. When both groups of mice were allowed to generate MDP hapten-modified tumor cells in the tumor mass in situ by intratumoral injection of MDP hapten, an appreciable number of growing tumors in the BCG-presensitized but not in the unsensitized group were observed to regress. In the second model, a growing X5563 tumor mass was removed by the surgical resection 9 days after the tumor implantation. Approximately 90% of C3H/He mice receiving such treatment died from tumor metastasis by about 30 days after the tumor resection. However, immunization of mice with MDP hapten-coupled X5563 tumor cells subsequent to the tumor resection resulted in an increased survival rate. Such protection from the tumor metastasis was appreciably stronger when compared to the protection obtained by immunization with MDP hapten-uncoupled tumor cells. The mice surviving in both models were also demonstrated to retain X5563 tumor-specific immunity. These results indicate that the presentation of MDP hapten-modified tumor cells to BCG-sensitized recipients results in potent tumor-specific immunity which contributes to the regression of the primary tumor or inhibition of metastatic tumor growth.