Age-dependent experimental tumor dissemination of murine melanoma B16

Female C57BL/6 Jena mice, 3-, 12-, and 18-month-old, were inoculated intravenously (i.v.) with syngeneic melanoma B16 cells. The number of experimental lung metastases, counted 21 days after tumor inoculation, was significantly higher in older hosts. Pretreatment of young adult mice with immunosuppressive dose of cyclophosphamide considerably increased the number of lung nodules. The number of lung metastases was reduced when young and old animals were pretreated or treated with Poly (I:C). Similar treatment of mice with two other immunomodulators (thymalin and diacetyl-splenopentin 5) was practically without effect on metastasis formation. It is suggested that the higher number of experimental metastases of melanoma B16 in aged mice is mediated by immuno-senescence.