Brief Communication: Transformation of Rhesus Foreskin Cells by Mason- Pfizer Monkey Virus 1,2

SUMMARY-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. Tumorigenic potential of Ihe transformed cells was indicated by their ability 10 induce palpable masses at the site of inoculation in newborn rhesus monkeys.-J Nat Cancer Inst 48: 191 3-1917 J 1972. CHOPRA (1) demonstrated by electron micros-copy virus particles, resembling those of the oncogenic RNA type, in a spontaneous carcinoma of a rhesus monkey. The budding extracellular particles resembled B-type particles but differed from them by the absence of characteristic surface spikes (2). The Mason-Pfizer monkey viru