cDNA phage display for the discovery of theranostic autoantibodies in rheumatoid arthritis

Rheumatoid arthritis (RA) is the world's most common autoimmune disease mainly characterized by a chronic inflammation of multiple synovial joints. Rheumatologists now have a whole range of treatment options including glucocorticoids (GCs), classical synthetic and biological disease-modifying antirheumatic drugs (cs- and bDMARDS), resulting in a tremendous improvement in treatment outcomes for RA patients over the last two decades. Despite this progress, the choice of treatment regimen to achieve stable remission at the individual patient level still largely depends on trial and error. In this review, the need for novel theranostic markers that can predict a patient's response to methotrexate, the standard first-line csDMARD treatment, is discussed. Like in many autoimmune diseases, the majority of RA patients form a whole range of autoantibodies. We aim to find novel theranostic autoantibody markers using serological antigen selection, a high-throughput technique that uses cDNA phage display to identify novel antigen targets. We have constructed a barcoded cDNA phage display library from the synovial tissue of three RA patients by fusing cDNA products to the filamentous phage minor coat protein VI. This library contains a large proportion of full-length genes and gene fragments that are cloned in frame with the phage gene VI. By screening this library for antibody reactivity in serum samples of patients from the CareRA trial, which compared different intensive treatment strategies based on csDMARDs and a step-down GC schedule, our cDNA phage display library has great potential for the discovery of novel theranostic autoantibody biomarkers.