Mechanisms for recognition of tumor antigens and mediation of anti-tumor effect by noncytolytic Lyt-2+ T cell subset

The mode of anti-tumor function in vivo of noncytolytic Lyt-2+ T cells from C3H/He mice hyperimmune to syngeneic MH134 hepatoma was investigated in a double diffusion chamber system which was recently established in our laboratory. C3H/He mice were implanted intraperitoneally with the double diffusion chamber unit in which each chamber contained either L3T4+ T cell-depleted MH134-hyperimmune spleen cells plus mitomycin C-treated MH134 tumor cells or other syngeneic X5563 viable tumor cells plus normal spleen cells as a source of macrophages. Inclusion of anti-MH134 Lyt-2+ T cells together with MH134 tumor cells in one chamber resulted in comparable growth inhibition of viable X5563 tumor cells in the other chamber to that obtained by unfractionated MH134-hyperimmune spleen cells. The induction in the Lyt-2+ T cell-containing chamber of anti-tumor effect to be delivered into the other chamber was dependent on the co-existence of Ia-positive adherent cells along with Lyt-2+ T cells. Although adherent cell-depleted Lyt-2+ T cells regained the inducibility of anti-tumor immunity when supplemented with splenic adherent cells, the addition of adherent cells pretreated with chloroquine failed to restore the ability of Lyt-2+ T cells to induce their anti-tumor effect. In addition, paraformaldehyde-treated MH134 tumor cells instead of untreated tumor cells were not capable of activating Lyt-2+ T cells. These results indicate that a portion of Lyt-2+ T cells exerts their anti-tumor effect by a mechanism distinct from direct tumor cell lysis and that their activation for mediation of this type of tumor immunity requires the recognition of tumor antigens processed and presented by Ia-positive adherent cells.