Malignant Transformation by Polyoma Virus

Since the pioneering work of Rous. most research on tumor viruses has been carried out by oncologists rather than by virologists. However, with the recent rapid development of new knowledge concerning the basic mecha­ nisms involved in cytolytic infections with animal viruses, the attention of virologists has been turned to the same questions in the transformation of normal animal cells to malignant cells by the action of tumor viruses. Yet. even now, the amount of such research is limited chiefly because of a lack of available tumor virus-cell systems which lend themselves to modern molecu­ lar biological techniques. The polyoma virus first isolated and studied by Stewart et al. (1) has been investigated by a number of virologists for two reasons. First, it is a more interesting virus since it has the potential of producing a large variety of tumor types in its natural animal host [Stewart et al. (2)]; and, secondly because it can be studied quantitatively by modern virological methods. Although capable of causing malignant transformation in both in vivo and in vitro systems it nevertheless produces a cytolytic infection under certain conditions, and, therefore, can be quantitated in tissue cultures using the plaque technique [Dulbecco & Freeman (3)]. Furthermore, being able to agglutinate guinea pig red blood cells, it can be quantitated by hemagglutina­ tion and through the hemagglutination inhibition (HI)! test can be specifi­ cally identified with ease [Eddy et al. (4)). Since its natural host is the mouse, the availability of many susceptible inbred lines of laboratory mice make it possible to relate in vitro tissue culture phenomena to tumor production in the intact whole animal. This paper will review and evaluate the more important recent research contributions concerning mechanisms of polyoma virus transformation, the relationships between virus and the cell after transformation, and some of the virus-specific properties of the transformed cells. These items will first be considered for the �n vivo transformation and then for that occurring in in vitro systems.