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

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 had been treated with erythropoietin at the time of their initiation. The properties of three permanent cell lines in serial passage for over 2 years are described. Each has an aneuploid karyotype. Only the immature hematopoietic cells of the first line have metacentric chromosomes. They grow 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 subcutaneous inoculation into syngeneic hosts. Stimulation of differentiation induced after treatment with dimethyl sulfoxide identifies the cells of the first 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 subcutaneous inoculation of 10(6) cells. All three 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.