Leukemogenicity and cell transformation mechanisms in vitro by Gross murine leukemia virus: analysis of virus subpopulations

Protection from spontaneous lymphoma development in SJL/J(v+) mice neonatally injected with dualtropic SJL-151 virus

In previous studies dualtropic type C retroviruses were isolated from spontaneous B-cell lymphomas that appear with a high incidence in SJL/J(v+) mice. In this report the possible in vivo pathogenic effect of one cloned dualtropic isolate, designated SJL-151, was investigated. SJL/J(v+) and CBA/J mice, neonatally injected with SJL-151 alone or in combination with SJL-ecotropic virus, were initially studied for virus recovery 4-8 weeks after infection by spleen cell cocultivation with mouse SC-1 and mink ML indicator cells. Whereas ecotropic virus was easily detected in treated mice, dualtropic virus was recovered only from the spleen cells of animals coinfected with SJL-ecotropic and SJL-151 viruses. With a panel of monoclonal antibodies the recovered dualtropic viruses showed an antigenic profile similar to that of the originally injected SJL-151 virus. Whereas virus-injected mice did not show lymphoma induction or acceleration, a remarkable decrease in spontaneous lymphoma incidence was observed in the SJL/J(v+) mice receiving SJL-151 virus alone. A virus-specific antibody response was detectable in these mice, but a similar serum reactivity was also demonstrated in SJL/J(v+) mice coinfected with SJL-ecotropic virus and SJL-151 virus, which subsequently developed lymphomas with the usual high incidence, thus rendering an antibody-mediated protective mechanism untenable. The possibility of viral interference, as an alternative mechanism for lymphoma prevention, is discussed in view of the findings that persistence of SJL-151 virus or de novo generation of dualtropic virus did not occur in aged SJL/J(v+) mice injected neonatally with SJL-151 virus alone.

Leukemogenesis by Gross passage A murine leukemia virus: expression of viruses with recombinant env genes in transformed cells

Gross passage A murine leukemia virus (MuLV) derived from extracts of C3Hf/Bi mouse leukemias has been shown to be a virus complex consisting of ecotropic, xenotropic, and recombinant, dualtropic MuLV components. The three virus components were distinguished biochemically by differences in the molecular weights and peptide maps of their primary env gene products synthesized in infected cells in vivo and in vitro. Virus expression was studied in primary leukemias induced in C3Hf/Bi mice by Gross passage A virus extracts and by the individual ecotropic and recombinant MuLV components that were isolated in vitro. Our findings suggest that expression of the recombinant MuLV component of the Gross passage A virus complex is necessary and sufficient for the induction of leukemias in C3Hf/Bi mice. In contrast, induction of leukemias by the ecotropic virus component appears to involve generation of a second virus with characteristics of recombinant, dualtropic MuLV.