Occurrence of Focal Three-dimensional Proliferation in Cultured Human Cells after Prolonged Infection with Herpes Simplex Virus

The occurrence of focal three-dimensional proliferation was observed in human conjunctiva cells in culture after prolonged infection with herpes simplex virus at 30 degrees C. and in KB cells infected with herpes virus at 37 degrees C. for several months in the presence of pooled human serum. This atypical growth pattern consisted of many discrete piles of cells 15 to 20 cells thick scattered over a monolayer of cells. Three-dimensional growth appeared only in the presence of 10 to 20 per cent of selected human sera. When horse serum was substituted for human serum growth was in an ordinary monolayer. The abnormal growth pattern of this cell line (C-4 line) has remained stable through continuous culture for over 2 years and was observed consistently in each of 25 clones isolated from the parent culture. Repeated tests for the presence of persisting infectious virus and for herpes virus antigen in the cells were negative. Comparison of the C-4 cell line with control conjunctiva cells revealed no significant difference in multiplication rate or in range of viral susceptibility, but the C-4 line was found to be more sensitive to ultraviolet irradiation.