Cryopreservation of Varicella-Zoster Virions without Loss of Structural Integrity or Infectivity

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Abstract
Varicella-zoster virions present in infected cells or in a cell-free state were freeze-dried without loss of structural integrity or infectivity. Generally, yields of > 5 log10 foci/ml (infected cells) or > 4 log10 plaque-forming units/ml (cell-free virus) were recovered from varicella-zoster virus-infected human melanoma cells before and after lyophilization in phosphate-buffered media containing 0.1-1.0 M sucrose. Virus frozen in solutions lacking sugar had little or no residual infectivity after vacuum sublimation was completed. Visualization by EM demonstrated large numbers of enveloped virions in the virus preparations lyophilized in media containing sucrose; virus subjected to freeze-drying in buffered solutions without sugar consisted mainly of naked nucleocapsids. Water analyses by Karl Fischer titration suggested that residual moisture retained by sugar prevented disenvelopment of the varicella-zoster virion.