Analytical Validation of a pre-Industrial Prototype Assay for Anti-Aβ Autoantibody ultrasensitive quantification in patients with CAA-ri and ARIA-E of Alzheimer’s disease Immunotherapy

Objective: Cerebral Amyloid Angiopathy-related inflammation (CAA-ri) is a rare autoimmune encephalopathy characterized by the (sub)acute clinicoradiological manifestation of amyloid-related imaging abnormalities-edema (ARIA-E) in patients with Alzheimer’s disease (AD) and CAA. 1 Although the term ARIA-E was coined to define the radiographic adverse events of AD immunotherapy with monoclonal antibodies targeting beta-amyloid (Aβ) plaques of AD, the recent natural history and response to treatment outcomes study of CAA-ri suggests ARIA-E is the radiographic manifestation of iatrogenic CAA-ri, as a reflect of the downstream Abs-mediated immune effects on Aβ clearance pathways. Paralleling therapy induced ARIA-E, CAA-ri is associated with increased cerebrospinal fluid (CSF) concentration of autoantibodies (aAbs) against Aβ, particularly in APOE4 carriers with CAA and AD comorbidity. In this framework, the CSF dosage of aAbs is becoming increasingly recognized as the most advanced candidate fluid biomarkers for overcoming current limitation of MRI in the diagnosis of both CAA-ri and ARIA-E. In fact, the diagnosis of both conditions is currently based on clinical and radiological criteria alone, which, however, demonstrated to be challenging in recognizing the complex biological heterogeneity of the condition and in predicting outcomes after occurrence of an ARIA-E index event. The lack of specific and sensitive biomarkers other than MRI alone often leads to the risk of misdiagnosis and makes difficult decision-makings both in trials and in the real clinical practice. In this framework, the need for a fluid biomarker assay to improve diagnostic accuracy and therapeutic monitoring of CAA-ri and ARIA-E represent an urgent international priority. Materials & Methods: analytical validation of an ultrasensitive assay for the quantification of aAbs. Preliminary biomarker validation study on the clinical utility of the aAbs test in the iCAB International and ARIAisCAAri sample cohort of patients with CAA, CAA-ri, AD, and healthy controls. Results: This assay demonstrated excellent analytical performance with a CV <10% for within and between run Precision, Trueness, Parallelism, and Recovery and an excellent ultrasensitive quantification in the range of pg/mL for LLOQ. Preliminary evidence showed the effectiveness of the aAbs testing in CSF in distinguishing CAA-ri patients from CAA (P<0.001) and remission phase CAA-ri (P<0.001), in a small clinical case series. Our results highlighted the potential of the aAbs in the diagnosis of CAA-ri. If confirmed in a large sample cohort of patients, the CSF testing for aAbs may have the requirements to become a companion diagnostic biomarker for mitigating the risk of ARIA-E and for therapeutic monitoring in AD immunotherapy.