Immune response to leukemia virus and tumor-associated antigens in cats

Cats represent an unusually valuable model for studying the role of the immune response to leukemia, lymphoma, and other mesodermal neoplasms. The agents that cause spontaneous feline leukemias, lymphomas, and fibrosarcomas, the feline leukemia and sarcoma viruses, are well characterized. A specific tumor cell membrane antigen, designated the feline oncornavirus-associated cell membrane antigen (FOCMA) has also been described. Feline leukemia and feline sarcoma viruses are antigenically indistinguishable, and FOCMA is common for both. Both laboratory-induced and spontaneous feline leukemias, lymphomas, and fibrosarcomas are available for study. A clear correlation has been shown between the resistance of cats to development of lethal tumors following inoculation of feline sarcoma virus and the presence of high humoral antibody titers to FOCMA. The geometric mean antibody titer to FOCMA for cats that resisted growth of fibrosarcomas was more than 20-fold higher than the mean for cats that succumbed to lethally progressing tumors. Cats with induced or spontaneous leukemia or lymphoma also have either no detectable FOCMA antibody or very low levels. Conversely, some cats resist development of leukemia or lymphoma following natural exposure to feline leukemia virus in leukemia cluster households, and these cats have high FOCMA antibody titers. These results support the concept of a natural immunosurveillance mechanism against leukemia or lymphoma development in an outbred mammalian species.