Viruses do replicate in cell-free systems

Abstract

Klingeborn et al. (1) reported a systematic study of the infectivity of transmissible spongiform encephalopathy (TSE) infectious agent generated de novo in cell-free reactions. They convincingly demonstrated the generation of new TSE infectivity in reactions primed by infected brain homogenates. Absence of infectivity in control reactions with brain homogenates lacking prion protein (PrP) supports the requirement of host PrP for in vitro replication of the agent. Based on these findings, the authors assumed this new infectivity derives from a small proportion of newly generated misfolded PrP. They then concluded that “because viruses do not replicate in cell-free conditions, this result is against the concept that the prion infectious agent is a virus” (1).