In 1949, in preliminary notes, we recorded the fact that the in vitro propagation of the poliomyelitis viruses may be accomplished in suspended cell cultures of various types of human tissues. The present paper details the procedures we have employed in the preparation and maintenance of suspended cell cultures for this purpose, and summarizes observations on the behavior of poliomyelitis viruses in such cultures, as observed during the past 4 years.

Each of 3 antigenic types of poliomyelitis virus has been propagated in suspended cell cultures of human embryonic skin and muscle tissue, in cultures of human embryonic brain tissue and in cultures of mature human kidney tissue. In addition it has been demonstrated that one or more of these 3 types of virus will multiply in cultures of various other human embryonic tissues, including intestine, adrenal and spleen. Likewise, mature human tissues including thyroid, foreskin, and testis have been successfully employed for the cultivation of the Lansing strain as well as materials from two tumors, an embryoma of the kidney, and a neuroblastoma. Poliomyelitis virus has also been cultivated in monkey kidney cultures.

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.

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