Determinants of the ability of malignant fibroma virus to induce immune dysfunction and tumor dissemination in vivo

Abstract The relationship of virus-induced immunological dysfunction and tumor dissemination was studied using two related tumor-causing leporipoxviruses: malignant fibroma virus (MV) and Shope fibroma virus (SFV). Recombinant viruses, produced by transferring MV's 10.7 kb Bam HI C fragment to SFV, replicate in lymphocytes and suppress lymphocyte function in vitro . Those recombinants that replicate in lymphocytes and suppress lymphocyte function in vitro share about 3.5 kb from MV's C fragment. Some recombinants mimic MV in producing immune suppression and disseminated virus infection in vivo . Other recombinants, even some that are highly immunosuppressive in vitro (e.g. R71), only variably induce immune suppression in vivo , and do not cause disseminated disease. A segment of DNA from MV that transfers to Shope fibroma virus almost all of MV's virulence in vivo was identified.