Immunotherapy of lethal metastases by lymphocytes sensitized against tumor cells in vitro.

To learn whether tumor metastases can be prevented by the immune system, we developed a model for the treatment of mice with syngeneic lymphocytes sensitized against tumor cells in vitro. Mice were given subcutaneously tumor cells that spontaneously metastasized to the lungs. The tumors developing locally were surgically removed and the mice were inoculated with sensitized lymphocytes 1 day later. Prevention of death by lung metastases was the measure of immunotherapy. Only approximately equal to 30-40 percent of mice receiving control treatment survived, whereas approximately equal to 70 percent survived that received lymphocytes sensitized in vitro against the tumor cells. Hence sensitization of syngeneic lymphocytes against tumor cells in vitro and injection of the lymphocytes into the host after removal of a local tumor prevented the development of lethal metastases.