Oncogenic Transformation of Rat Embryo Fibroblasts with Photoinactivated Herpes Simplex Virus: Rapid In Vitro Cloning of Transformed Cells

Abstract

Rat embryo fibroblasts (REF) were transformed in vitro with photoinactivated herpes simplex virus. Low passage (7-10) HSV-transformed rat cells (t-REF-line G) produced multiple tumors in 49% of newborn rats with a latent period of 20-24 wk. An in vitro cloning procedure for transformants in the uncloned t-REF-line G cells produced clonal lines which varied from non-oncogenic to clonal lines producing tumors with shorter latent periods (10-14 wk) compared to uncloned cells. At passage 30, t-REF-line G-clone 1 cells produced rapidly growing tumor in 100% of the newborn rats with a latent period of only 2-3 wk. Tumor cells (RFS 12-22-75) established in culture produced tumors within 2 wk after s.c. inoculation of weanling rats (100% with tumors) and they were transplantable to 100% of inoculated adult rats. Histopathological examination of all tumors produced in newborn, weanling or adult rats revealed large, poorly differentiated malignant fibrosarcomas; metastatic tumors were observed in the lungs of 10-20% of newborn rats inoculated s.c. with RSF cells. About 25-50% of the clonal transformed or tumor cells synthesized HSV-specific-antigens detected by immunofluorescence. HSV-transformed and tumor cells are resistent to superinfection by the homologous tranforming virus. Since the in vitro cloning procedure for transformant cells can readily segregate cells producing clonal lines varying in oncogenic potential, the procedure might have useful application in elucidating HSV oncogenesis.