Effect of Different Sera on Growth and “Spontaneous” Neoplastic Transformation of Mouse Fibroblasts In Vitro

Abstract

Murine fibroblasts undergo “spontaneous”, malignant transformation when grown in calf serum (CS) and horse serum (HS), whereas this process is less frequent and delayed in fetal bovine serum (FBS). To test whether this effect is due to a different growth-stimulating capacity of the sera on murine fibroblasts or to a selection of CS and HS in favor of preneoplastic or early neoplastic cells, normal and spontaneously transformed BALB/c fibroblasts were cultivated for 4 days in Eagle's minimal essential medium with 0.5 or 10% FBS, CS, or HS. Tumoral fibroblasts but not normal cells grew in the presence of 0.5% of the 3 sera. At 10% concentration FBS, which in a parallel experiment produced less spontaneous transformation than CS, stimulated a better growth of normal cells than an equal amount of CSand HS, but the 2 latter sera induced a greater replication of spontaneously transformed fibroblasts than of normal cells. Nine fibrosarcomas obtained by syngeneic backtransplantation of cell lines cultivated in CS and FBS were assayed for immunogenic properties by transplantation methods. The same was done with 4 sarcomas obtained by spontaneous neoplastic transformation in vivo of murine fibroblasts grown within cellimpermeable diffusion chambers kept in the peritoneum of mice for 420–460 days. Lack of immunogenicity was found in 8 of 9 in vitro-induced tumors and 2 of 4 in vivo counterparts, whereas the remaining 3 sarcomas had a significant degree of immunogenicity.