The lymphocyte response to primary moloney sarcoma virus tumors: Definition of a non‐specific component of the in vitro cellular hyporeactivity of tumor‐bearing hosts

Adult CBA mice injected with Moloney Sarcoma Virus (MSV) developed tumors within 5 to 8 days which usually completely regressed within 1 month. Maximal tumor size was variable, occurring between 10 and 15 days. Lymphocytes from these animals were examined for activity against syngeneic target cells bearing the Moloney Leukemia Virus (MLV) ‐associate dcell‐surface antigen. As previously found with BALB/c mice, the lymphocytes were found to be active in microcytotoxicity tests against these target cells; however, the animals which were bearing tumors at the time of testing were found to have the least active lymphocytes. These animals were also immunized against H‐2d antigens 10 to 13 days prior to testing and their lymphocytes tested for cytotoxicity against H‐2d target cells in 51Cr release assays. It was found that the tumor‐bearing animals, by day 10‐16 after MSV infection, had lymphocytes which were significantly less active against the H‐2d antigens than those of animals tested prior to the development of tumor or those in which the tumors had regressed. It was thus concluded that a component of the cellular hyporeactivity, as measured by in vitro cytotoxicity in these primary MSV tumor bearing hosts, is non‐specific.