Characterization of guinea‐pig embryo cells transformed by Kirsten mouse sarcoma virus

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Abstract
Guinea‐pig embryo cells were transformed in vitro by the Kirsten strain of mouse sarcoma virus (Ki‐MSV). The transformed cells were found to release infectious virus continuously and produced high titers of group‐specific, complement‐fixing antigen characteristic of the murine leukemia—sarcoma virus complex. Foci of transformed cells were similar in appearance to those obtained with Ki‐MSV in mouse and rat cells. The transformed cells produced RNA‐dependent DNA polymerase and type‐C virus particles with a density of approximately 1.15 g/ml in sucrose gradients by 3H‐uridine labelling. The transformed cells from one line produced tumors when transplanted into newborn guinea‐pigs. A number of focus‐derived clonal lines and “normal cells” derived from infected cells were isolated and characterized. All the focus‐derived lines were found to be MSV producers. The Ki‐MSV grown in guinea‐pig cells replicated efficiently in guineapig and NRK cells but very poorly in mouse cells. A non‐cytopathic type‐C virus‐producing line (clone No. 2) was isolated. A non‐focus‐forming virus grown in guinea‐pig embryo cells (clone No. 2) rescued infectious MSV by direct cocultivation with Ki‐MSK non‐producer NRK cells. The rescued MSV virus was neutralized by Ki‐MSV antiserum and produced foci readily in mouse, rat and guinea‐pig cells.