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Reduction in cellular tumorigenicity after mycoplasma infection and elimination of mycoplasma from infected cultures by passage in nude mice.

The mouse L-cell derivative A9, deficient in hypoxanthine phosphoribosyltransferase and previously shown to be highly tumorigenic in nude mice, was infected deliberately with known mycoplasma species and transplanted in nude mice in order to determine the effect of the adventitious organisms on tumor initiation and growth rate. Two of the most common mycoplasma strains found in contaminated cell cultures, Mycoplasma hyorhinis and Acholeplasma laidlawii , have been used, since both of these possess high levels of endogenous hypoxanthine phosphoribosyltransferase activity that can be utilized as a quantitative measure of cell contamination. The presence of mycoplasma particles in the infected cultures was verified independently by electron microscopy and a fluorescent staining technique. The results indicate that contamination of cell lines by mycoplasma can significantly alter the tumor initiation and growth rate of normally tumorigenic cells injected in nude mice. In addition, at least for the 2 mycoplasma strains described here, the passage of contaminated cells in nude mice invariably resulted in their complete elimination from the cultures. Since many animal cell lines are tumorigenic in nude mice, this observation suggests that passaging cell in vivo in nude mice may be a simple and effective means of obtaining mycoplasma-free cells from contaminated cell cultures.