All mice were housed at RML in an AAALAC-accredited facility in compliance with guidelines provided by the Guide for the Care and Use of Laboratory Animals (Institute for Laboratory Animal Research Council). Experimentation followed RML Animal Care and Use Committee approved protocol #2014–095. Generation of tg66 transgenic mice expressing human PrP were described previously . These mice are on a FVB/N genetic background, and are homozygous for a transgene that encodes human prion protein MM129. Tg66 mice overexpress human PrP at 8–16-fold levels higher than normal physiologic levels and have been shown to be susceptible to vCJD, sCJD and mouse-adapted 22 L scrapie [37, 38].