PMCA to demonstrate the efficacy of prion inactivation methods on reusable medical devices: a relevant alternative to animal bioassays

Validation of prion inactivation processes for medical devices relies on in-vivo experimental protocols. However, bioassays are costly, long (1-2 years) and ethically disputable. Additionally, results obtained with one prion strain - for example, 263K (hamster-adapted strain originating from sheep scrapie) - cannot be easily extrapolated to relevant human prion strains, further questioning the utility of bioassays. Over the past two decades, cell-free prion amplification assays have emerged as potential alternatives to bioassays. Rather than measuring prion infectivity, they quantify prion seeding activity (i.e. the capacity to convert the normal prion protein into the disease-associated isoform). The results obtained from an optimized cell-free assay termed 'miniaturized-bead protein misfolding cyclic amplification' (mb-PMCA) with four processes using three different prion strains - 263K and two human prions derived from variant and sporadic Creutzfeldt-Jakob disease - were compared with published bioassays using the same three strains and processes, when available. Tests performed on reference processes (steam, sodium hydroxide, sodium hypochlorite) and low temperature H₂O₂ sterilization (STERRAD NX^TM Advanced cycle) showed perfect alignment between mb-PMCA and available bioassays. STERRAD NX^TM Advanced cycle was efficacious against all three prion strains. These data confirm that PMCA, particularly mb-PMCA, is a relevant alternative to animal bioassays for the assessment of prion inactivation processes, and highlight the interest of some low temperature H₂O₂ sterilization cycles.