At the ongoing AD/PD 2024 International Conference on Alzheimer’s and Parkinson’s Diseases, the development and progress of blood-based biomarkers (BBMs) in Alzheimer’s disease was a key theme with multiple symposia and forums focused on this topic.

Current clinical biomarkers are hampered by limitations as they require either expensive positron emission tomography (PET) neuroimaging scans or a highly invasive lumbar puncture to collect a cerebrospinal fluid (CSF) sample for testing. Non-invasive, relatively cheap BBMs have the potential to revolutionise many aspects of the Alzheimer’s clinical continuum, from diagnosis and monitoring disease progression to screening and prognosis. Additionally, the development of BBMs will likely be crucial in bringing novel therapeutics and disease-modifying therapies (DMTs) to lower-income countries where PET imaging and CSF assays are either not available or not accessible for the majority of the population.

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In 2018, the National Institute on Aging–Alzheimer’s Association (NIA-AA) published a framework for the diagnosis of Alzheimer’s based on a biological rather than symptomatic framework using an A/T/N classification system for Alzheimer’s disease biomarkers: biomarkers targeting amyloid pathology, tau pathology, and neurodegeneration, respectively. However, these guidelines only included CSF and PET biomarkers.

With BBMs soon to enter clinical practice for diagnostic purposes, these guidelines are currently being updated by the Alzheimer’s Association and are expected to be published later in 2024. The updated guidelines will include plasma phosphorylated-tau (p-tau) 217 as part of the Core-1 biomarkers for diagnosis, alongside amyloid PET imaging and established CSF biomarkers. However, experts in a BBM forum held at AD/PD 2024 on 6 March noted that approval by regulatory bodies is still required in Europe before BBMs can become part of clinical practice, and although there are some BBMs now available in the US for Alzheimer’s diagnosis, experts noted that soon the requirement for FDA approval will be introduced for these biomarkers.

It was noted that in a primary care setting, physicians already request blood tests routinely for a variety of reasons and therefore physician education around implementing BBMs for Alzheimer’s into patient care pathways in the primary care setting should be relatively straightforward. However, it was also highlighted that while BBM results are more objective compared to PET scans, they can still require some interpretation when results fall around the threshold level indicating the likelihood of Alzheimer’s, particularly if multiple BBMs are assessed at one time, which could be a potential barrier to their uptake in the primary care setting. Further, an assessment of a patient’s cognition and function will still be essential for diagnosing and staging the disease and as such, the experts highlighted that these new BBMs should not be rushed into clinical practice and that the development of clear guidelines and physician education will be a vital step in them becoming routinely used.

In addition, both during a forum specifically focused on BBMs and during a symposium sponsored by the Alzheimer’s Drug Discovery Foundation (ADDF), the potential role of BBMs in improving clinical trials was discussed. Currently, Alzheimer’s clinical trials have a high burden for patients, in part due to the high neuroimaging burden with the requirement for PET scans at various time points throughout a trial. Introducing BBMs to clinical trial protocol to replace, or at least reduce, the high neuroimaging burden, could help to encourage more patients to participate in trials, and it will reduce the cost of the clinical trials, something particularly important for smaller biotechs looking to develop drugs for Alzheimer’s.

According to GlobalData’s drugs database, there are about 100 currently active smaller biotech companies (defined as having <5 products) with Alzheimer’s drugs at the clinical development stage. Further, BBMs could help streamline the recruitment process, enabling a quicker, more cost-effective screening process to determine patient eligibility for the trial.

While we are nearing the use of BBMs in clinical practice for diagnosis, more research is required for BBMs to have an impact in other stages of the clinical continuum, such as for measuring disease progression, drug efficacy, and as prognostic biomarkers in screening. Developers are including BBMs as secondary endpoints in clinical trials to help characterise how the BBM readings change in relation to drug use, with the future aim that BBMs can be used to determine the efficacy of a drug.

In Phase III trials with Eisai’s Leqembi (lecanemab) and Biogen’s Aduhelm (aducanumab ), plasma p-tau181 has been evaluated. In Phase III donanemab trials, plasma p-tau217 has been evaluated. In these trials, treatment with the drug was correlated with decreases in the level of plasma p-tau in the blood, and typically the longer the treatment duration, the greater the decrease that was seen. Once these BBMs have been fully validated, they could be used to determine the efficacy of these drugs in reducing amyloid in the brain and as such when treatment can be stopped in favor of an alternative treatment that may be able to maintain low amyloid or prevent rebuild-up in the brain.

Overall, experts were excited for the future of BBMs in Alzheimer’s disease, noting that as drug development continues it pushes biomarker research forward, and visa versa: with continued biomarker development, it enables drug development to push forward. As companies begin to target the preclinical or pre-symptomatic patient population, it will likely push research on BBMs for screening forward, with the ultimate goal being early detection before symptoms, and drugs that can prevent the disease altogether