Comparative Susceptibility of Cell Cultures to Vaccinia Virus: Application to the Standardization of Smallpox Vaccine

Abstract

Vaccinia virus from calf lymph was propagated in bovine embryonic cell culture derived from lung, kidney or muscle tissue, in HeLa cells and in monkey and rabbit kidney epithelium cultures. Yields of virus following one passage in bovine lung, muscle and kidney and monkey kidney cell cultures were comparable and ranged from 105.5 to 107.5 TCD50 per ml. When serial passages of vaccinia virus in these tissues were assayed at the 13th and 25th passages, titers had decreased from that of the first passage but had stabilized between 103.7 and 106.7 TCD50 per ml. The infectivity of these preparations for rabbit skin had considerably decreased. When plaquing techniques were applied to the titration of vaccinia virus, the titers obtained following a 6 hour attachment period were in close agreement with those obtained by roller tube titration. Ten commercial smallpox vaccines were assayed in roller tube tissue cultures, rabbits, and embryonated eggs. Of the systems tested monkey kidney cell cultures proved most sensitive to infection by the virus. Repeated titration of several of these vaccines by plaque and roller tube methods in monkey kidney cell culture and on the scarified rabbit skin emphasized the reliability of tissue culture assay when compared with the highly variable rabbit scarification method of assay. When calf lymph virus exposed to 60[degree] C was similarly assayed, no virus was detectable after 10 minutes, while the titer in monkey kidney tissue culture was approximately 4.3 TCD50 per ml. In view of the sensitivity of monkey kidney cell cultures to vaccinia virus, a tissue culture method of smallpox vaccine assay is recommended.