Inhibition of cell-mediated cytotoxicity against tumor-associated antigens by suppressor cells from tumor-bearing mice.

Spleen cells from mice bearing primary tumours induced by Moloney strain of murine sarcoma virus (M-MuSV) strongly inhibited the in vitro generation of specific secondary cell-mediated cytotoxic response of spleen cells from M-MusV regressor mice. These suppressor cells were resistant to treatment with anti-theta serum and complement or to X-irradiation. It appeared that suppressor cells may have had a role in limiting the host's immune response against tumor growth.