The info about the trial can be found here, with a little update addition at the top with a link to the October development as well: https://www.broadinstitute.org/news/clinical-trial-prion-disease-drug-candidate-begins-enrolling-participants

There has never been a treatment for prion diseases before. They're rare, but once you get one (like Creutzfeldt-Jakob Disease ie CJD) you experience rapidly progressive dementia followed by death, generally within the span of 6 months. The mortality rate is 100%

For now.