Mediation of in vivo Tumor‐neutralizing Activity by Lyt‐2 + as Well as L3T4 + T Cell Subsets *1

The present study reexamines the cell surface nature of T cells mediating in vivo protective tumor immunity with the use of anti‐L3T4 and ‐Lyt‐2 antibodies. C3H/HeN mice hyperimmune against syngeneic MH134 hepatoma or MCH‐1‐A1 fibrosarcoma were prepared by intradermal (id) inoculation of viable tumor cells followed by surgical resection of the tumor and by repeated challenges with viable tumor cells. Spleen cells from these mice were fractionated into L3T4 + or Lyt‐2 + T cell subset by treatment with anti‐Lyt‐2 or ‐L3T4 antibody plus complement (C). Winn assays performed by utilizing such fractionated T cells have revealed that both L3T4 + and Lyt‐2 + T cell subsets from hyperimmune mice produced complete tumor protection. Flow microfluorometry study illustrated that the treatment with anti‐L3T4 or ‐Lyt‐2 antibody plus C resulted in the complete isolation of L3T4 − Lyt‐2 + (Lyt‐2 + ) or L3T4 + Lyt‐2 − (L3T4 + ) T cell subset, respectively. This contrasted with the failure of treatment with anti‐Lyt‐1 antibody plus C to isolate all T cells expressing Lyt‐2 marker. It was further demonstrated that each subset of T cells exerted its anti‐tumor effect in a tumor‐specific way and without a requirement for the other alternative subpopulation of unprimed T cells. These results indicate that Lyt‐2 + T cell subset can be successfully isolated by treatment with anti‐L3T4 but not with anti‐Lyt‐I antibody plus C, and that each single subset of Lyt‐2 + and L3T4 + T cells can function as in vivo effector T cells.