Biological properties of cell lines derived from Moloney virus-induced sarcoma.

Two cell lines derived from a primary MSV-M-induced tumor in a BALB/c mouse were studied. One line (MS-2) was subject only to continuous tissue culture transfer (tct). After 21 tct, MS-2 cells produced progressive tumors (MS-2 tumors) in syngeneic hosts. The second cell line (MS-2T) was established by cultivation of a MS-2 tumor. The ability to produce progressive tumors decreased with increased number of tct, in both cell lines. The virus content of MS-2 and MS-2T cells was very low, as shown by uridine incorporation and electron microscopy. Immmunofluorescence tests demonstrated that antigens different from the viral MSV-M antigens were present on the cell lines, and that antigenic changes occurred with increased number of tct. Serum of mice bearing progressive MS-2 tumors reacted with MS-2T cells when these cells produced progressive tumors and did not react with MS-2 cells when they produced regressing tumors. MS-2 cells producing regressing tumors reacted with serum from mice in which the MS-2 tumor had regressed and with serum from mice immunized with MS-2T cells at late tct when they were poorly oncogenic. The antigenic changes seemed, therefore, to parallel the decrease of malignancy. A chromosomal analysis carried out on MS-2 and MS-2T cells, when both produced progressive tumors, showed a modal number of 48 and 44, respectively. MS-2T cells showed a large acrocentric chromosome. In contrast, the MS-2 cells at late tct, when they gave regressing tumors, showed a modal number of 60 and a wide range of distribution of chromosome number.