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Growth Properties of Polyoma Virus-induced Hamster Tumor Cells^*

( Department of Pathology, New York University School of Medicine, New York, N.Y.)

Hamster polyoma virus-induced sarcomas, when serially cultivated under rigidly controlled conditions, uniformly gave rise to established lines within ten to twenty generations of life in vitro. Normal hamster embryo fibroblasts, carried in culture under identical conditions, initially grew as well as the tumor cells but always failed to develop into established lines; none continued to grow past ten generations in vitro. The neoplastic cells appeared to be more mutable than the normal fibroblasts and developed into established lines by undergoing changes leading to greater ability to grow autonomously in vitro. In the course of establishment of such lines, the cells underwent a reduction in the rate at which they produced tumors when injected into animals. However, this capacity could be fully restored by a single animal passage while the cells retained the properties previously acquired in vitro.

Embryonic fibroblasts when infected in vitro with polyoma virus also develop into established lines. Such lines, tested in the newborn hamster, were found to have neoplastic properties comparable to those of tumors produced in vivo. One cell line was studied in detail throughout its development; after transformation by the virus it was initially unable to produce tumors but on continued growth in vitro acquired increasing capacity to do so. Full neoplastic potential was not reached until the transformed cells had grown through over 40 cell generations in vitro. The capacity of polyoma cells to produce tumors was not repressed when these cells were injected in mixtures with normal cells in great excess.

^* Aided by grants from the U.S. Public Health Service.

Received 12/13/62.