Ly-1+2- suppressor T cells inhibit the expression of passively transferred antitumor immunity by suppressing the generation of cytolytic T cells.

The results of this study confirm and extend previous findings from this laboratory by showing that the suppressor T cells that are generated during progressive growth of the P815 tumor and inhibit the antitumor cytolytic response in adoptively immunized T-cell-deficient recipients are of the Ly-1+2- phenotype. Thus, Ly-2+ cytolytic effector T cells and suppressor T cells in the system can be distinguished by the complete resistance of suppressor T cells to elimination by anti-Ly-2-antibody-plus-complement treatment. The suppressor cells in this system are different, therefore, from those in most other systems in which suppressor cells, like cytolytic T cells, are Ly2+ or the equivalent rat or human phenotype. The present results also more clearly define how suppressor T cells inhibit the expression of antitumor immunity by showing that passively transferred suppressor T cells inhibit the production of cytolytic T cells in adoptively immunized T-cell-deficient recipients, but not the antitumor function of cytolytic T cells already generated. Finally, the results show that the expression of passively transferred antitumor immunity in T-cell-deficient recipients requires the participation of noncytolytic Ly-1+2- donor T cells. It is apparent, however, that T cells of this phenotype have no direct antitumor activity but function, instead, to "help" in the generation of cytolytic T cells in the recipient.