Transformation of Rhesus Foreskin Cells by Mason-Pfizer Monkey Virus

When rhesus foreskin cells were infected with Mason-Pfizer monkey virus and subsequently seeded into semisolid agar medium, numerous colonies grew. Colonies picked and replated produced cells with altered morphology. The cultures contained both multinucleated and giant cells and demonstrated loss of contact inhibition on continued culture. The cells also satisfied other criteria for in vitro transformation, i.e., growth in semisolid agar medium and factor-free medium. The cells released virus as determined by infectivity assays and electron microscopy. Tumor-igenic potential of the transformed cells was indicated by their ability to induce palpable masses at the site of inoculation in newborn rhesus monkeys.