Macrophage-mediated inhibition of melanoma cell growth in nude mice.

The effects of macrophages or sera from tumor-transplanted or control syngeneic and allogeneic mice on the latency and growth rate of P51 murine melanoma cells were determined after transplantation into congenitally athymic (nude) mice (tumor neutralization test). Syngeneic macrophages from tumor-bearing mice (TBM) inhibited melanoma growth in the nude mouse more than control macrophages, additionally macrophages from sensitized allogeneic mice inhibited melanoma growth to a greater degree than did allogeneic control macrophages. Sera from TBM inhibited melanoma growth as compared to control cells alone. Macrophages obtained after 14 days were also cytolytic towards the melanoma target in vitro. Despite the growth of large local masses, no evidence of distant metastases was found. The nude mouse thus provides an appropriate model for this tumor to portray in vivo immunotherapy.