A direct relationship between immune competence and the subcutaneous growth rate of a malignant murine lung tumor.

SUMMARY We have studied the transplantability and growth in syngeneic hosts of a malignant alveolar cell carcinoma of the BALB/c mouse lung. In untreated mice, the cancer can be established with fewer than 100 cells and grows with a volume doubling time of 3. 1 days. Total-body irradiation of the host with 500 R 2 hr prior to s.c. inoculation with tumor cells does not affect the transplantability of the tumor but significantly suppresses its growth rate. This suppression of the growth rate is not associated with a generalized body weight loss and cannot be induced by localized irradiation. Injection of hydrocortisone acetate prior to tumor inoculation or use of immunologically crippled senescent hosts yields a similar suppression. Further, suppression of the growth rate of the cancer by total-body irradiation can be reversed by transplantation of syngeneic lymph node or spleen cells immediately after irradiation. It is unlikely that this reduced growth rate of s.c. tumors in immunosuppressed hosts results from in hibition of immunological reactions which stimulate growth or from a preferential loss of â€oeblocking†• factors, since metastasis proceeds more rapidly in immunosuppressed hosts and splenectomy does not slow the growth of the s.c. tumor.