INDUCTION OF SARCOMAS IN ATHYMIC MICE

During the course of serial passage of 50 human xenografts in the athymic mouse over a period of 5 yr, 2 cases of induction of sarcomas were observed in the murine stromal tissue associated with the human xenografts. Both times the growth of the murine sarcomas overtook that of the human xenograft. This change was monitored by analysis of the lactate dehydrogenase isozyme profile and histology of each passage of the human xenografts in the athymic mice. The 2 murine sarcomas were subsequently established in tissue culture. The sarcoma cell lines were found to be malignant by morphological and growth characteristics and were tumorigenic. They contained large amounts of murine leukemia virus when assayed for reverse transcriptase activity by infection of mouse SC-1 cells and BALB/c and NIH Swiss fibroblasts with filtered supernates, and some type C virus particles were observed by EM in tumor tissues. The presence of murine sarcoma virus could not be demonstrated by in vitro transformation of fibroblasts or sarcoma formation in vivo with cell free filtrates. Preliminary biochemical data indicate that the sarcomas are extremely high in plasma membrane ATP phosphohydrolase.