Studies on the cultivation of poliomyelitis viruses in tissue culture. I. The propagation of poliomyelitis viruses in suspended cell cultures of various human tissues.

Assay of the infectivity of materials removed from the tissue cultures was perfomred by the classical method of titration in animals and also by the technique of titration in vitro employing the cytopathogenic effect of the poliomyelitis viruses as an indicator of viral activity. Materials from cultures prepared with human embryonic skin-muscle tissues, kidney tissue, or brain tissues yielded the highest infectivity titers. Serial propagation in suspended cell cultures of human embryonic skin-muscle tissue was achieved for 23 passages with the Lansing strain, for a cumulate period of 331 days in cultivation, and for 15 passages with the Brunhilde strain, during a total period of 267 days. Throughout these prolonged periods of cultivation, virus production in each instance remained essentially constant as assayed by the in vitro technique. The titers as determined in vitro were in most cases equivalent to those observed in the central nervous system of the infected animal. However, in experiments with Lansing virus prolonged cultivation in human tissues was associated with a marked decline in apparent infectivity titer of the agent for the mouse. Likewise, in one experiment with Brunhilde virus, a significant decrease in the apparent infectivity titer for the monkey was observed.