COMPARATIVE STUDIES IN ROUS SARCOMA WITH VIRUS, TUMOR CELLS AND CHICK EMBRYO CELLS TRANSFORMED IN VITRO BY VIRUS : III. MALIGNANCY IN VIVO OF CELLS TRANSFORMED IN VITRO BY VIRUS

Virus production and release, cell longevity, and cloning efficiency of chicken embryo fibroblasts infected with Rous sarcoma virus

Continuous virus production is a characteristic of chicken embryo fibroblasts (CEF) infected and transformed by a nondefective Schmidt-Ruppin subgroup A Rous sarcoma virus. This virus production has been examined with particular attention to the amount of newly budded virus which remained cell-associated, and to the amount and degree of viral aggregation at the cell surface and in the fluid tissue culture medium. The total biologically active virus associated with a Schmidt-Ruppin subgroup A Rous sarcoma virus-infected CEF culture was divided almost equally between that portion of virus which was present in the fluid medium and that portion which was cell-associated. Various mechanical and enzymatic methods were used to remove cell-bound virus and to disperse aggregates of virus in the tissue culture medium to assess cell production of virus per hour accurately, which was determined as an average of 16.4 focus-forming units per cell per hour. With appropriate culture conditions, it was found that Schmidt-Ruppin subgroup A Rous sarcoma virus-infected and -transformed CEF replicated faster, could be passaged more times, and grew to higher cell densities than did normal CEF and CEF infected with a subgroup A Rous associated virus. Subgroup A Rous sárcoma virus-infected CEF cloned with much lower efficiency than did subgroup A Rous associated virus-infected CEF or normal CEF. Experiments employing a temperature-sensitive mutant of subgroup A Schmidt-Ruppin Rous sarcoma virus- and Rous associated virus-infected CEF indicated that the poor cloning efficiency of Schmidt-Ruppin subgroup A Rous sarcoma virus infected cells was not due to the constant production of virus but was probably related to some property associated with transformation of the cell by Rous sarcoma virus.

Low Malignancy of Rous Sarcoma Cells as Evidenced by Poor Transplantability in Turkeys

Homologous and isologous transfers of Rous sarcoma cells in turkeys indicate that growth of the implanted cells contributes little, if at all, to the formation of these neoplasms. Infection of normal host cells by virus appears to be, at least in this species, the major factor in the induction and progressive growth of Rous sarcomas.