Effect of age on pulmonary metastases and immunotherapy in young and middle-aged mice

Background: We used B16-F1O (B16) melanoma tumor cells and syngeneic C57BL/6 (B6) mice as a study model for pulmonary metastases, to better understand whether or not there exist differences in tumorigenicity and in the effectiveness of immunotherapy as a function of host age (1-, 3-, 12- and 24-month-old). Methods: Intravenous injection of B16 melanoma cells were administered to B6 mice of different ages with/without interleukin (IL)-2 and IL-12 daily treatment. Tumor growth, splenocyte function, serum cytokines (IL-10, interferon-γ, vascular endothelial growth factor) and survival were compared. Results: The study showed that, without IL-2 and IL-12 treatment, middle-aged mice suffering from pulmonary metastases had fewer pulmonary metastases and better survival than younger mice suffering from pulmonary metastases. Three days' IL-2 plus IL-12 treatment could not prolong mice survival, but prolonged treatment significantly improved the survival of both the younger and older tumor-bearing mice, especially the older mice, despite the fact that the younger mice had a better serum cytokine and splenocyte cellular immune response to cytokine treatment. Conclusion: The young B6 mice that suffered from B16 pulmonary metastases had a poorer prognosis than the middle-aged mice. Short-term IL-2 plus IL-12 treatment is ineffective in prolonging survival, and a longer duration of treatment is needed. This kind of immunotherapy was effective in both the young and middle-aged mice, but it was more effective in the middle-aged mice.