Expression of the Defective “S+L−” Type Murine Sarcoma Virus Genome in Human Amnion and Lung Cells

Murine sarcoma virus (MSV) rescued from cloned sarcoma-positive leukemia-negative (S+ L-) mouse cells was used to obtain a single cell clone, S+L− HuACh, from a single-hit terminal focus in human AV-3 amnion cells. Second generation MSV, rescued from S+L− HuACh cells by superinfection with RD-114 virus, was used to generate 3 clones of S+L− cells derived from 3 separate MSV foci in L-132 human lung cells. S+L− human amnion and lung cell clones demonstrated certain characteristics of S+L− mouse cells: All 4 S+L− human cell clones were transformed, expressed the genetically stable murine leukemia virus group-specific antigen marker, and con- tained cryptic MSV rescuable by superinfection with compatible helper-type viruses that conferred host range properties on the rescued MSV pseudotypes. S+L− human cells differed from S+L− mouse cells in that the human cells did not release detectable C-type virus-like particles. S+L− human cells also lacked detectable quantities of the viral core protein reverse transcriptase. Although similar to non producer Kirsten-MSV transformed mouse cells, S+L− human cells failed to release detectable MSV after iododeoxyuridine induction.