Systemic adoptive transfer of immunity and low‐dose irradiation eradicate metastases of 13762a rat mammary adenocarcinoma

Rats cured of poorly immunogenic 13762A tumor by a combination of surgery and cyclophosphamide (CY) treatments produced peritoneal exudate cells (PEC) that prevented tumor growth when transferred to naive recipients, but they were ineffective against established tumor. A highly immunogenic 13762A clone (18A) induced PEC lymphocytes that completely reversed the growth of established primary tumor and of lymph‐node metastases. 18A‐immune PEC alone strongly inhibited tumors of 7 days' duration, but only moderately suppressed 14‐day tumors, and had no effect on 21‐day tumors. Irradiation (450 R) of rats prior to tumor transplantation improved the effectiveness of the PEC given at 7 days, but the benefit had gone by 14 days. Long‐term T‐cell depletion prior to tumor challenge allowed PEC inhibition of 7‐ and 14‐day tumors, but not 21‐day tumors. The most potent strategy was the administration of 450 R followed immediately by immune PEC. When rats with 21‐day tumors were so treated, the metastases grew temporarily to a maximum diameter of 2‐5 cm and then completely regressed. We concluded that a combination of immune T cells and 450 R can cure established, massive metastases, probably through a combination of an increase in the numbers of T‐cell effectors and elimination of suppressor cells.