Tumor-specific T helper activity can be abrogated by two distinct suppressor cell mechanisms.

Tumor-specific helper T cell activity was detected in the spleens of tumor-bearing mice using a sensitive, simple and reproducible in vitro assay based on those previously described for soluble hapten-carrier antigens. Helper activity disappears when the tumor is large. This is coincident with the appearance of two distinct types of suppressor cells: (a) T cells which suppress tumor-specific T helper responses and (b) non-T cells which are nonspecific in their action.