Splenectomy, suppressor cell activity, and survival in tumor bearing rats

Young female rats of the Fischer strain were subjected to splenectomy at 10 weeks of age. Three weeks later, these animals and a comparable group of intact animals were inoculated subcutaneously with 3 × 10⁶ cells of the syngeneic Ward colon carcinoma. Tumor growth was recorded by serial measurement. Lymph node cells from control, intact tumor-bearing, and asplenic tumor-bearing animals were tested for reactivity in mixed lymphocyte culture (MLC) and for ability to suppress the allogeneic mixed lymphocyte reaction. At 3 weeks after tumor inoculation, lymphocyte reactivity in MLC was somewhat depressed in asplenic tumor-bearing hosts but severely depressed in intact hosts (P < 0.001); suppressor activity was demonstrable in intact hosts but not in asplenic hosts (P < 0.001). At 5 weeks, lymphocyte reactivity in MLC was severely depressed in both groups; suppressor cell activity was present in both groups and differences were no longer significant. Median survival of intact tumor-bearing animals was 97 days after inoculation (P < 0.0001 by the log-rank test), and 120 days in asplenic animals (P < 0.001). We conclude that both depression of lymphocyte reactivity and onset of suppressor activity are delayed in asplenic tumor-bearing animals. Host survival was significantly prolonged.