Transformation of DBA/2 mouse fetal liver cells infected in vitro by the anemic strain of Friend leukemia virus.

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Abstract
Fetal liver cells of DBA/2 mice were infected with the anemic strain of Friend leukemia virus (FLV-A), which has no spleen focus-forming virus (SFFV) activity. The infected cells were grown in medium with or without erythropoietin. Transformed lines were isolated only from the infected cultures that were treated with erythropoietin at the time of their initiation. The properties of 3 permanent cell lines in serial passage for over 2 yr are described. Each has an aneuploid karyotype. Only the immature hematopoietic cells of the 1st line have metacentric chromosomes. They grown in suspension, as do the erythroleukemic lines derived from leukemic spleens of FLV-infected mice, and clone on agar. They produce tumors resembling reticulum cell sarcomas upon s.c. inoculation into syngeneic hosts. Stimulation of differentiation induced after treatment with dimethyl sulfoxide identifies the cells of the 1st line as being erythroid in origin. The two other lines are adherent and epithelioid in appearance. These lines may have originated from the nonhematopoietic cells present in fetal liver. No tumors were produced after the s.c. inoculation of 106 cells. All 3 lines synthesize virus. The virus is attenuated for leukemogenicity and has no SFFV activity. The transforming event appears to be specific, because fetal liver cells from C57BL/6 mice, which are resistant to the induction of leukemia by FLV, were not affected by the virus. Malignant transformation of erythroid cells by FLV-A in vitro confirms the in vivo findings that SFFV may not be a necessary prerequisite for the induction of erythroleukemia in susceptible hosts.