Retrovirus particle production in three of four human teratocarcinoma cell lines.

In spite of a long and intensive search, human retroviruses have not yet been demonstrated unambiguously (for review see Pimentel 1979). The electron microscopic detection of retrovirus particles in human term placentas by Kalter and others (Kalter et al. 1973; Vernon et al. 1974) represents at present the most convincing piece of evidence that human oncornaviruses may exist. As our attempts to isolate these viruses from placentas or to cultivate placentas in vitro have not succeeded, tumors containing tissues histologically similar to that of the placenta were investigated for virus expression. Among other tumors, teratocarcinomas from males and choriocarcinomas from females were studied. In contrast to choriocarcinomas, most of the teratocarcinomas can be induced to produce retrovirus particles in tissue culture.