PRNP and variant Creutzfeldt-Jakob disease: We repeated the same six conditions of inoculation with PrP-KO mice, as described in Table 1; PrP-KO mice do not develop vCJD, and thus, any PrPTSE detected in their blood must have come from the inoculum, allowing us to determine the kinetics of clearance of PrPTSE remaining from the inoculum after each condition of inoculation.