Endogenous RNA tumor viruses are activated during chemical induction of murine plasmacytomas

Plasmacytomas are induced in BALB/c mice by the intraperitoneal injection of pristane (2,6,10,14-tetra-methylpentadecane) after a latent period of six months and more [Anderson, P. N. & Potter, M. (1969) Nature 222, 994-995]. Spleen cells mesenteric lymph node cells, thoracic lymph node cells, and peritoneal exudate cells were prepared from pristane-treated and control uninjected BALB/c mice during the course of a 10-month period, and these cell suspensions were tested for the release of infectious murine leukemia viruses. Endogenous ecotropic and xenotropic murine leukemia viruses were expressed in pristane-treated mice during the latter part of the tumor induction period, in those cell populations in which transformed plasma cells appear, namely, peritoneal exudate cells and thoracic lymph node cells. The significance of preferential expression of both ecotropic and xenotropic murine leukemia virus in target cell populations following the administration of a carcinogen is discussed in terms of the possible formation of an oncogenic variant virus.