Progressive growth of fish tumors after transplantation into thymus-aplastic (nu/nu) mice

The nude mouse does not reject xenografts of malignant and nonmalignant tissues of mammalian or avian origin, due to a deficiency of functional T-lymphocytes. In this study, tissue from a cold-blooded vertebrate, a teleost fish, was for the first time successfully transplanted to Swiss albino nu/nu mice. Malignant melanotic melanoma of Xiphophorus transplanted to nude mice showed progressive growth and could be serially passaged. In vitro culture experiments revealed that the fish tumor cells adapt to the physiological conditions of the mammalian host, most obviously to the body temperature. On the other hand, fish-specific morphological characters and biochemical features, e.g., expression of a melanoma-associated antigen, were retained. This experiment demonstrates the enormous capacity of the melanoma cells to adapt to severe changes in their environment, which even enables them to overcome the physiological barriers between such taxonomically distant vertebrate groups as fish and mammals.