Pathogenic risk of endogenous retrovirus infection in immunodeficient hosts

To investigate the pathogenic risk of endogenous retroviruses (ERVs) infection in immunodeficient hosts, the ERV of N-type ecotropic murine leukemia virus (MuLV) isolated from SL mice, a kind of mice containing considerable infectious ERV particles determined with SC–XC test and developing leukemia spontaneously with average of high frequency of 30% and incubation period of 315 days, was inoculated intraperitoneally into newborn CBA nude mice. The distinct marker of splenomegaly for leukemia was observed in 33% of homozygous (nu/nu) and 17% of heterozygous (nu/+) of CBA nude mice with average incubation period of 310 days and 432 days post-inoculation, respectively. Furthermore, the ERV induced leukemia in both the SL mice and CBA nude mice was identified to be B lymphatic, transplantable and with rearrangement of the Evi-1 locus. The higher induction of leukemia and rearrangement of the Evi-1 locus in CBA nude mice are considered to be dependent on the lower immune status of the hosts. These findings indicate that the ERV could present the host immune dependent leukemogenesis in immunodeficient hosts through the Evi-1 gene rearrangement and suggest that screening of ERVs may be necessary in clinical transplantation or transfusion.