To appreciate the significance of RT-QuIC, one must return to the conceptual problem that defined prion research for decades. Prions are infectious agents composed not of nucleic acid but of misfolded protein, a proposition famously advanced by Stanley Prusiner in 1982 and foreshadowed by theoretical work from J.S. Griffith and by radiation experiments in the 1960s suggesting that the scrapie agent could replicate without a genome. The central mechanism is templated conversion: a misfolded, aggregated form of the prion protein acts as a seed that forces the normal, protease-sensitive form of the protein to refold into the pathological conformation. This seeding model, articulated by Jarrett and Lansbury in 1993 as a kind of one-dimensional crystallization, implied that the infectious agent could in principle be detected and amplified in a cell-free system, if only the right conditions could be found.

Caughey’s laboratory delivered the crucial early proof. In 1994, working with Kocisko, Lansbury, and colleagues, his group reported the cell-free formation of protease-resistant prion protein, demonstrating that aggregates of the abnormal protein could induce the conversion of the normal protein outside any living cell. Follow-up papers in 1995 showed that these aggregates could drive the conversion of protease-sensitive prion protein to the protease-resistant state and that strain-specific properties of scrapie prions could propagate non-genetically, a finding with profound implications for how prion diversity is encoded. The same year, Caughey and Lansbury invoked the fictional ice-nine metaphor from Kurt Vonnegut’s novel Cat’s Cradle to describe the templating chemistry of scrapie infection, a seed that crystallizes everything it touches. These experiments established the mechanistic foundation on which all subsequent seed amplification technologies would be built.

The leap from proof of principle to practical detection required solving a sensitivity problem. Early cell-free conversion assays were slow and comparatively insensitive, and the field’s gold standard for detecting infectivity remained the animal bioassay, which took months or years. In 2001, Claudio Soto’s group introduced protein misfolding cyclic amplification, which used repeated rounds of sonication to amplify prion aggregates in brain homogenate. Caughey’s laboratory, together with Atarashi and colleagues, took a different route: in 2007 they described ultrasensitive detection of scrapie prion protein using seeded conversion of recombinant prion protein, and in 2010 Wilham, Orrú, and colleagues published the first full description of RT-QuIC. The assay’s elegance lay in its components. Recombinant prion protein serves as the substrate, tiny amounts of misfolded seed from a biological sample initiate its aggregation, and the aggregation is tracked in real time by a fluorescent dye, thioflavin T, that lights up as amyloid fibrils form. Gentle shaking, or quaking, accelerates the reaction in standard microplate readers.

The result was a diagnostic revolution. RT-QuIC could detect prion seeding activity with sensitivity comparable to animal bioassays but in hours rather than months, and it required no infectious material beyond the sample itself. Successive refinements pushed the technology further. In 2014, Orrú and colleagues reported in the New England Journal of Medicine that nasal brushings could be used to diagnose Creutzfeldt-Jakob disease with remarkable accuracy, and in 2015 the same team showed that cerebrospinal fluid testing with RT-QuIC achieved high sensitivity and specificity for sporadic CJD. International ring trials confirmed the assay’s robustness across laboratories, and second-generation protocols standardized the substrate and reaction conditions. Today, RT-QuIC on cerebrospinal fluid is incorporated into diagnostic criteria and surveillance guidelines for human prion disease issued by bodies such as the CDC and the European Centre for Disease Prevention and Control, and it has been extended to an astonishing range of easily accessible tissues, including olfactory mucosa, skin punch biopsies, hair roots, tear fluid, and even placental tissue.

Perhaps the most consequential extension of the platform came when Caughey’s group and others realized that the same seeding logic applies to other misfolded proteins implicated in neurodegenerative disease. Alpha-synuclein, the protein that aggregates in Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy, was adapted to RT-QuIC formats beginning around 2013, with parallel development of the related alpha-synuclein seed amplification assay by Shahnawaz and colleagues. Groveman and colleagues published a rapid, ultrasensitive alphaSyn RT-QuIC in 2018 for quantifying pathological alpha-synuclein seeds in brain and cerebrospinal fluid. The clinical payoff has been dramatic: large multicenter studies, including analyses within the Parkinson’s Progression Markers Initiative, demonstrated that cerebrospinal fluid alpha-synuclein seed amplification can identify Parkinson’s disease with high accuracy, and longitudinal work published in The Lancet Neurology in 2025 showed that the kinetic measures of the assay carry diagnostic and prognostic value. Researchers have since detected alpha-synuclein seeds in skin, olfactory mucosa, duodenal biopsies, and serum, opening the door to minimally invasive diagnosis at early stages of disease.

The same logic has been applied to tau, the microtubule-associated protein whose aggregates define Alzheimer’s disease and a family of frontotemporal dementias collectively called tauopathies. Kraus and colleagues showed in 2019 that RT-QuIC could selectively detect tau aggregate conformers of Alzheimer’s disease, and Metrick and colleagues developed a single ultrasensitive assay capable of discriminating tau aggregates of Alzheimer’s disease from those of Pick disease. Salt-modulated amplification protocols now allow classification of tauopathies directly from brain homogenates, and tau seeding activity has been detected in skin biopsies, where it helps differentiate tauopathies from synucleinopathies. The platform has expanded further still: TDP-43 seeds have been measured in cerebrospinal fluid and olfactory mucosa of patients with amyotrophic lateral sclerosis and frontotemporal dementia, superoxide dismutase 1 aggregates have been detected in neural tissue and cerebrospinal fluid from ALS cases, and even misfolded insulin has been targeted with a dedicated RT-QuIC assay.

Beyond human diagnostics, RT-QuIC has become an indispensable tool for surveillance and control of animal prion diseases, particularly chronic wasting disease in deer and elk, which continues to spread across North America and beyond. The assay enabled antemortem detection of prions in saliva, urine, blood, and feces of infected cervids, longitudinal studies of prion shedding, and detection of prions on environmentally relevant surfaces and in venison processing environments. Ear-notch testing of free-ranging and farmed deer is now feasible, and recent work has found prions in the blood of healthy-appearing white-tailed deer, underscoring the challenge of silent carriage. The assay has also been turned on itself in a constructive way: because it quantifies residual seeding activity, it has become a standard method for evaluating prion decontamination procedures, testing disinfectants such as hypochlorous acid, sodium hypochlorite, and commercial formulations against multiple prion strains on laboratory surfaces.

The technology continues to evolve in directions that Caughey championed: higher throughput, greater sensitivity, and broader accessibility. Hofmeister ion comparisons achieved million-fold sensitivity enhancements in seed amplification assays for biospecimens, magnetic particle extraction concentrates prions from large-volume samples, and nanoparticle-enhanced Nano-QuIC has overcome inhibitors in blood to detect alpha-synuclein seeding activity in Parkinson’s patients. Microfluidic Micro-QuIC platforms promise rapid on-site amplification and visual detection, while digital seed amplification assays bring single-molecule counting to TDP-43 quantification in cerebrospinal fluid. In parallel, the assay has become a workhorse of therapeutic research, serving as a screening tool for anti-prion drug candidates and as a readout in human cerebral organoid models of Creutzfeldt-Jakob disease, where recent work has identified oligosaccharyltransferase complex inhibition as a promising treatment strategy for rodent and human prions.

What emerges from the review is a portrait of a scientific legacy built on collaboration, standardization, and an almost obsessive attention to the practical details of assay performance, from substrate selection, such as the remarkably versatile bank vole prion protein, to buffer chemistry and shaking parameters. The authors are careful to note that seed amplification technology has been developed through the seminal contributions of many eminent scientists and that the breadth of the field now extends far beyond any single laboratory or any single review. Yet the through-line is unmistakable. A question that began with the strange chemistry of scrapie, pursued for decades by Byron Caughey and his collaborators, has grown into a family of ultrasensitive assays that now detect, discriminate, and quantify the pathological protein seeds of prion disease, parkinsonism, tauopathy, and motor neuron disease. As the field moves toward standardization, data sharing, and clinical deployment of alpha-synuclein and tau seed amplification assays, the tree of discoveries that grew from a single prion seed continues to spread its branches across medicine.

Subject of Research: Development and legacy of the RT-QuIC seed amplification assay for ultrasensitive detection of prions and other misfolded proteins

Article Title: From a prion seed to a tree of discoveries: Byron Caughey’s RT-QuIC legacy in protein misfolding research

Article References: Groveman, B. R., Vascellari, S., Bongianni, M., Hughson, A. G., Zanusso, G., & Orrú, C. D. (2026). From a prion seed to a tree of discoveries: Byron Caughey’s RT-QuIC legacy in protein misfolding research. Acta Neuropathologica, 152(1), Article 44. https://doi.org/10.1007/s00401-026-03094-3

Image Credits: AI Generated

DOI: 10.1007/s00401-026-03094-3

Keywords: RT-QuIC, prion disease, Byron Caughey, protein misfolding, alpha-synuclein, tau, Creutzfeldt-Jakob disease, Parkinson's disease, seed amplification assay, chronic wasting disease, TDP-43, biomarkers

The central biological puzzle has never changed. Prion diseases, including Creutzfeldt-Jakob disease in humans, scrapie in sheep, and chronic wasting disease in deer, are driven by the misfolding of a normal cell-surface protein, the prion protein PrP, into a self-propagating pathogenic conformer known as PrP-Sc. Unlike viruses or bacteria, this infectious entity carries no genome; its biological information is encoded purely in protein conformation. Once a misfolded seed appears, it templates the conversion of the native, protease-sensitive PrP into more of the pathological form, which then aggregates into amyloid fibrils that accumulate in the brain and destroy neurons. Caughey recognized early on that every step of this chain, from the initial conformational conversion to fibril assembly, disassembly, and clearance, represents a potential point of therapeutic attack.

Some of the earliest and most influential work from the Caughey laboratory concerned the structural chemistry of the scrapie-associated protein itself. In 1991, using infrared spectroscopy, Caughey and colleagues demonstrated that the protease-resistant PrP 27-30 core is dominated by beta-sheet secondary structure, a finding that established the conformational difference between the normal and pathological protein and set the stage for decades of structural pharmacology. This was followed by the discovery that sulfated glycosaminoglycans and dyes such as Congo red bind to PrP and block its pathological accumulation, providing the first chemical handles on the conversion process. These studies established a recurring theme: molecules that preferentially interact with amyloid-like surfaces or with the conversion intermediate can inhibit prion propagation, even if their potency in living animals remains limited by permeability and toxicity constraints.

Perhaps the most consequential technical achievement was the development of cell-free conversion assays. In the mid-1990s, Caughey and collaborators showed that aggregates of scrapie-associated PrP could induce the conversion of normal, protease-sensitive PrP to the protease-resistant state in a cell-free system. This single experiment provided powerful biochemical support for the protein-only hypothesis of prion replication and, more practically, created a screening platform. For the first time, researchers could monitor protein misfolding in real time, quantitatively, without infecting animals. The approach matured into real-time quaking-induced conversion, or RT-QuIC, an ultrasensitive amplification assay now used worldwide to detect minute quantities of prion seeding activity in cerebrospinal fluid and other tissues. RT-QuIC has become a clinical diagnostic cornerstone for sporadic and genetic Creutzfeldt-Jakob disease, and it also serves as a critical readout in therapeutic trials, allowing researchers to verify that a candidate treatment genuinely reduces the load of seed-competent misfolded protein.

Armed with these assays, the laboratory systematically screened thousands of drugs and natural products for anti-prion activity. The resulting chemical catalogue is remarkably diverse. Congo red and its analogues, sulfated polyanions, curcumin, synthetic peptides, degenerate phosphorothioate oligonucleotides, and cyclic tetrapyrroles such as porphyrins and phthalocyanines all showed the ability to inhibit protease-resistant PrP formation in cell culture or cell-free systems. Some of these compounds, notably certain porphyrins, extended survival in prion-infected mice after intracerebral challenge, while combination treatments demonstrated that pairing compounds with complementary mechanisms can enhance antiscrapie effects. Equally important was what these experiments taught about failure modes. Work on drug resistance revealed that prions can select for inhibitor-resistant conformations under selective pressure, much as viruses do, meaning that any future therapy must be designed with an eye toward the evolving conformational landscape of the infectious agent.

A second major line of investigation focused on the cell biology of the prion protein. Caughey’s group showed that the scrapie-associated form of PrP derives from a cell surface precursor that is sensitive to both proteases and phospholipases, implicating the plasma membrane as a site of conversion. The glycophosphatidylinositol anchor and the N-linked glycans of PrP were found to influence strain-dependent conformations, linking the molecule’s membrane context to its pathological folding pathway. This cellular perspective suggested therapeutic strategies that go beyond simply blocking conversion: relocating the normal protein substrate away from the compartments where conversion occurs, promoting its removal, or downregulating its expression altogether. Experiments in which neuronal depletion of PrP prevented disease and reversed early spongiform changes in infected mice validated the substrate-targeting logic, and the recent finding that depleting neuronal Ndst1 accelerates prion protein clearance and slows neurodegeneration shows that modifying the protein’s glycan environment remains a viable therapeutic direction.

More recent work from the group has pushed the substrate-targeting strategy into the era of modern nucleic acid therapeutics. Antisense oligonucleotides designed to reduce PrP expression have extended survival in prion-infected mice, and intracerebral infusion studies established proof of concept for delivering these drugs to the central nervous system. Newer reports describe divalent siRNA approaches and the inhibition of the oligosaccharyltransferase complex, which disrupts PrP maturation and effectively treats both rodent and human prions in model systems. Human cerebral organoids have emerged as a clinically relevant screening platform for Creutzfeldt-Jakob disease therapeutics, bridging the gap between cell lines and animal models. Together, these advances suggest that the long-elusive goal of an effective anti-prion treatment may finally be within reach of clinical translation, even though no approved therapy yet exists for these uniformly fatal diseases.

The review also emphasizes how high-resolution structural biology has changed the game. For decades, the infectious prion resisted atomic-level characterization because brain-derived fibrils are heterogeneous and difficult to purify. That barrier has now fallen. Cryo-electron microscopy structures of infectious mammalian prion fibrils, including anchorless RML prions and natural chronic wasting disease fibrils from deer, have revealed parallel in-register intermolecular beta-sheet architectures and defined the conformational motifs that distinguish prion strains. These structures confirm predictions made years earlier by hydrogen-deuterium exchange and other lower-resolution methods, and they open the door to genuine structure-based drug design: small molecules and designed peptides can now be engineered to bind specific pockets or surfaces on the pathogenic fibril rather than discovered by chance. Iterative machine learning approaches, already used to design potent inhibitors of alpha-synuclein and tau aggregation, are being adapted to the prion field, using fibril amplification assays with brain-derived seeds as the feedback loop.

One of the most striking lessons of this four-decade effort is its relevance far beyond the rare diseases that motivated it. Self-propagating misfolded proteins underlie Alzheimer’s disease, Parkinson’s disease, Lewy body dementia, and other common neurodegenerative conditions, and the methodological toolkit built in the prion field, from RT-QuIC and seed amplification assays to structure-guided inhibitor design and substrate-lowering nucleic acid drugs, has been exported almost wholesale to these larger fields. Sensitive detection of misfolded protein seeds in biofluids now enables early diagnosis and objective biomarker monitoring in clinical trials, while drug design pipelines that once screened blindly can target specific fibril polymorphs. The prion concept has also reshaped thinking about biosafety, with rigorous work on disinfectants such as sodium hypochlorite and Wex-cide defining how to inactivate these exceptionally resistant agents in clinical and laboratory settings.

The Caughey story is ultimately a case study in how persistent, mechanistically grounded basic research can convert a scientific pariah into a therapeutic roadmap. By elucidating disease biochemistry, insisting on the need to target conformational change, building assays that measure the pathogenic process directly, and integrating those assays with structural characterization and cell physiology, one laboratory’s quest for prion inhibitors has given neurodegeneration research its most rigorous experimental standards. As antisense oligonucleotides, siRNA platforms, prion vaccines, and structure-based small molecule design converge, the patients and families affected by these devastating diseases have, for the first time in the history of the field, multiple credible paths toward an effective treatment, each one built on foundations laid over forty years of work at the interface of chemistry, structure, and cell physiology.

Subject of Research: Development of therapeutic inhibitors targeting prion protein misfolding through biochemistry, structural biology, and cell physiology

Article Title: Life at the interface: Byron Caughey’s search for prion disease inhibitors through chemistry, structure, and cell physiology

Article References: Life at the interface: Byron Caughey’s search for prion disease inhibitors through chemistry, structure, and cell physiology. (n.d.). https://doi.org/10.1007/s00401-026-03080-9

Image Credits: AI Generated

DOI: 10.1007/s00401-026-03080-9

Keywords: prion diseases, prion protein, PrP-Sc, Congo red, RT-QuIC, antisense oligonucleotides, cryo-EM, drug discovery, neurodegeneration, protein misfolding, Creutzfeldt-Jakob disease, Byron Caughey