Oncogenic Effect of Tissue-Culture Preparations of Polyoma Virus on Fetal Mice

Abstract

Swiss mice inoculated late in fetal life with tissue-culture preparations of SE polyoma virus died earlier and had a higher incidence of tumors than animals inoculated shortly after birth. No histologic types of tumors were seen in the mice treated in utero that had not been seen previously in mice treated as newborns. Some of the treated mice were the offspring of mothers bred near mice that had been inoculated previously with polyoma-virus preparations. The incidence of salivary-gland tumors and renal lesions was significantly lower in mice from those mothers that had been indirectly exposed to inoculated animals than in mice from unexposed mothers. A comprehensive morphologic analysis of the tumors indicated interrelated patterns of development and behavior which are unique among murine neoplasms. Initially in organs where tumors developed, epithelial cells hypertrophied, formed intranuclear inclusion bodies, and degenerated. The tumors were composed of hyperplastic epithelial elements and proliferating undifferentiated cells that were limited in their capacity to invade adjacent tissues or metastasize. Some tumors regressed, while other caused death of the animal only by local growth in vital organs.