Oncogenicity of AKR endogenous leukemia viruses

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Abstract
Four biologically distinct groups of endogenous murine leukemia virus (MuLV) were isolated from AKR mice. These viruses include ecotropic XC+ MuLV that occur in high titer in normal tissues and serum of AKR mice throughout their life span, ecotropic XC- MuLV that are produced in high titers by leukemia cells, xenotropic MuLV that are readily demonstrable only in aged mice and polytropic MuLV that arise in the thymuses of aged mice as a consequence of genetic recombination between ecotropic and xenotropic MuLV. Viruses of each of these biological classes were assayed in AKR mice for their ability to accelerate the occurrence of spontaneous leukemia. Certain isolates of ecotropic XC- MuLV and polytropic MuLV had high oncogenic activity. These viruses induced 100% leukemias within 90 days of inoculation. Ecotropic XC+ MuLV that were obtained from AKR embryo fibroblasts and xenotropic MuLV that were obtained from the lymphoid tissues of aged AKR mice did not demonstrate oncogenic activity. These findings demonstrate fundamental differences between XC- and XC+ ecotropic MuLV that are found in leukemic and normal tissues, respectively, and point to the role of ecotropic XC- and polytropic MuLV in the spontaneous leukemogenesis of AKR mice.