The observation that human PrPC substrate support better PrPSc amplification when seeded with human vCJD agent than with any other source of vCJD/BSE agents, and that the murine PrPC substrate was poorly efficient at amplifying non-murine vCJD/BSE agents, concur with the general conclusions derived from cell free conversion assay. This evidence concerns the gene PRNP and variant Creutzfeldt-Jakob disease.