Clonal analysis of early and late stages of erythroleukemia induced by molecular clones of integrated spleen focus-forming virus.

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Abstract
The integrated proviral DNA of the polycythemia-inducing isolate of Friend spleen focus-forming virus (SFFVP) was identified in rat cell clones nonproductively infected with this replication-defective erythroleukemia virus and cloned in phage .lambda. vectors. These .lambda.SFFVP recombinants, .lambda.SFFVP502 and .lambda.SFFVP542, contain endonuclease EcoRI inserts of size 7.4 and 8.2 kilobases, respectively, and include full copies of the SFFVP genome along with host flanking sequences. Infectivity of the cloned SFFVP genomes was tested by a 2 step DNA transfer procedure involving transfection of the cloned DNA into 3T3 mouse fibroblasts or cotransfer of the cloned DNA into thymidine kinase-deficient 3T3 cells together with the cloned thymidine kinase gene of herpes simplex virus, followed by rescue of the transferred DNA by superinfection with a helper virus. Inoculation of the rescued virus into adult mice resulted in the appearance of spleen foci, rapid splenomegaly and polycythemia. Early after infection, sleen cell populations contained large numbers of cells capable of forming small erythroid colonies in vitro (CFU-E) in the absence of erythropoietin. Late after infection, these mice contained cells capable of forming macroscopic colonies (CFU-FV) in vitro. Molecular clones of SFFVP, in conjunction with a helper virus, induce the appearance of hemopoietic colony-forming cells characteristic of both the early and late stages of Friend leukemia.