Laboratory animals have long since been used extensively in bioassays for
prions in order to quantify, usually in terms of median infective doses [ID50], how infectious these pathogens are in vivo. The identification of aberrant
prion protein as the main component and self-replicating principle of
prions has given rise to alternative approaches for
prion titration. Such approaches often use
protein misfolding cyclic amplification (PMCA) for the cell-free biochemical measurement of
prion-associated seeding activity, or cell assays for the titration of in vitro infectivity. However, median seeding and cell culture infective doses (SD50 and CCID50, respectively) of
prions are neither formally congruent nor definitely representative for ID50 titres in animals and can be therefore only tentatively translated into the latter. This may potentially impede the acceptance and use of alternative methods to animal bioassays in
prion research. Thus, we suggest performing PMCA and cell assays jointly, and to check whether these profoundly different test principles deliver consistent results in order to strengthen the reliability and credibility of
prion ID50 assessments by in vitro methods. With regard to this rationale, we describe three pairs of PMCA and glial cell assays for different hamster-adapted
prion agents (the frequently used 263K
scrapie strain, and 22A-H
scrapie and BSE-H). In addition, we report on the adaptation of quantitative PMCA to human
variant Creutzfeldt-Jakob disease (vCJD)
prions on steel wires for
prion disinfection studies. Our rationale and methodology can be systematically extended to other types of
prions and used to further reduce or replace
prion bioassays in rodents.