The Generative Brain

Surf-PMCA, amplification test for variant CJD prions on steel surfaces used to evaluate decontamination (EFS TransDiag, Montpellier)

Surf-PMCA is a laboratory test, not a patient test. It was built by the TransDiag laboratory of the Etablissement Francais du Sang in Montpellier to measure whether prions survive on a steel surface after a cleaning or sterilisation step. Small stainless steel wires are contaminated with brain material from a variant CJD case or from a scrapie sheep, treated, and then amplified directly in a protein misfolding cyclic amplification reaction, so that any residual seeding activity on a single wire becomes detectable by western blot within about two weeks. The point of the method is to replace, or at least to triage, the animal bioassays that had been the only way to check decontamination against human prions. In 2020 the same group tested that premise by implanting treated wires in prion-susceptible mice and comparing the two readouts, and reported that they agree. Both papers report that several marketed prion decontamination reagents performed worse against vCJD prions than expected, which the 2020 paper links to their having been validated on a hamster strain. Information only, not medical advice and not guidance on instrument reprocessing.

Key facts

  • The assay uses stainless steel wires of 0.15 mm diameter cut into 3 mm pieces, contaminated in 96 well plates with 1 percent scrapie or 10 percent vCJD brain homogenate, dried and rinsed; after treatment each wire goes straight into a PMCA reaction with normal brain homogenate from transgenic mice carrying ovine or human prion protein, run for three to four rounds of sonication and 37 degree incubation with a one in ten transfer between rounds, then proteinase K digestion and western blot.
  • Abnormal prion protein was detected on a single wire down to a 10^-8 brain dilution for both the 127S scrapie strain and vCJD, with a dynamic range of about 6 to 7 logs, and all mock contaminated control wires stayed negative. The authors call the human prion work qualitative because only two independent vCJD series were run.
  • In the 2016 comparison of reference procedures against vCJD prions, sodium hypochlorite cleared the signal even at 0.2 percent and steam at 134 degrees left no positive wires, while steam at 121 degrees and 0.1 N sodium hydroxide were only partly effective, the latter estimated at about a 3 log reduction. The authors call this surprising given reports that BSE and vCJD prions are more heat resistant.
  • Six marketed reagents, anonymised A to F and described as validated by the French medicines agency, were tested in 2016 alongside water and peracetic acid controls. Results varied: one product cleared the vCJD signal, one performed no better than water, and several left detectable signal.
  • The 2020 study implanted treated wires intracerebrally in tgBov tg110 mice, which overexpress bovine prion protein about six times normal and are susceptible to low doses of vCJD prions, and compared attack rate and survival time with the Surf-PMCA result for the same treatment. The rankings matched: treatments that cleared seeding activity gave no transmission, partly effective treatments gave intermediate transmission, and several commercial products were largely ineffective.
  • Endpoint titration in the mouse model gave attack rates of 90 percent at 10^-1, 89 percent at 10^-2, 50 percent at 10^-3 and 10^-4 and 10 percent at 10^-5, making 10^-5 the detection limit and giving about a 4 log dynamic range, roughly 1 log less sensitive than the hamster 263K bioassay. The authors say the 50 percent endpoint titre could not be calculated accurately.
  • Amplicons produced by three Surf-PMCA rounds from a wire contaminated at 10^-7 transmitted disease to all inoculated mice at 338 days, close to the 342 days of the 10^-3 homogenate group, which the authors read as regeneration of at least 4 log units of infectivity in vitro.
  • The 2020 paper concludes that products approved on the hamster 263K model can fail against vCJD prions, so 263K validation may not predict vCJD decontamination, and offers Surf-PMCA as a rapid complementary screening tool rather than a replacement for the bioassay. It also flags that the wires were air dried, which may not reflect clinical conditions where devices stay moist.
  • Funding is named in both papers: the Alliance Biosecure Foundation for the Surf-PMCA project in 2016, and the French medicines and health products safety agency ANSM for the Prion MD Secure project in 2016 and 2020, with the funders stated to have had no role in design, analysis or the decision to publish.
  • Authorship sits with the EFS Montpellier group (Belondrade first, Bougard corresponding, in 2016 under the name Laboratoire TransDiag, UMR 1058, EFS Pyrenees-Mediterranee, and in 2020 under Pathogenesis and Control of Chronic Infections, EFS, INSERM, Universite de Montpellier), with the INRA prion virology unit at Jouy-en-Josas, the Montpellier university hospital biochemistry laboratory and, in 2020, CISA-INIA in Madrid.
  • The method has a small published footprint: a Europe PMC search for the term returns four records, the 2016 and 2020 papers and two Prion conference abstract collections.

Timeline

  1. 2016Surf-PMCA described in PLoS One, electronically published 22 January 2016, with detection at 10^-8 brain dilution on a single wire within two weeks and the first reagent comparison.
  2. 2019The bioassay comparison manuscript is received by mSphere on 9 September 2019 and accepted on 5 January 2020.
  3. 2020mSphere publishes the comparison on 29 January 2020, reporting agreement between residual seeding activity and residual infectivity in tgBov mice.
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