Electron-microscopic observations of polyoma virus-transformed mouse cells treated with specific immune serum.

Walls & Negroni (1966) reported the isolation in tissue culture of a transformed but non-malignant clone of cells from a polyoma virus-induced fibrosarcoma of C3H Bi mice. These cells, when inoculated into C.AH Bi mice, did not grow as tumours but immunized the animals against malignant cells derived from the same fibrosarcoma. Furthermore the serum from mice thus immunized prevents the growth in vitro of both malignant and non-malignant polyoma virus-transformed cells (the colonyinhibition test, Hellstrom & Sjogren, 1965). We describe in this note the morphological changes observed by electron microscopy in these cells treated with such immune serum in the presence of fresh guinea-pig complement. These changes provide an explanation for cell death and growth failure in vitro.