Engineered CAD5 cells expressing human prion protein with valine at codon 129 constitute the first robust dividing cell system capable of propagating and quantifying bona fide infectious human sporadic Creutzfeldt-Jakob disease prions with sensitivity comparable to transgenic mouse bioassays, enabling therapeutic screening and providing a faster, more cost-effective alternative to animal models for human prion research.

Prions are assemblies of misfolded proteins that cause transmissible, progressive neurodegenerative disease in humans and other mammals. Human prion diseases have particular public health and biological significance, both due to their transmissibility between hosts, and the mechanisms they share with many other neurodegenerative conditions. However, their study has been considerably impeded by the absence of a cell-based system capable of reproducibly propagating and quantifying bona fide human prion infectivity, which has been a goal for several decades.

Here, we describe the first robust, cell-based assay of human prion infectivity in dividing cells. We found that CAD5 cells expressing human prion protein instead of the endogenous mouse prion protein, replicate human prion infectivity from brain samples of patients with sporadic Creutzfeldt-Jakob disease (sCJD) expressing valine at codon 129 of the prion protein gene. Moreover, these cells quantify human prion infectivity with similar sensitivity to the current gold standard animal bioassay, at a fraction of the cost and time, maintain persistent infection that can be cured with an anti-prion treatment, and can be adapted for therapeutic screening. This novel system permits direct cell-based quantification and investigation of human prion infectivity for the first time.