THU0027 Non-response to rituximab therapy in reumatoid arthritis associates with incomplete disruption of the b-cell receptor repertoire in the peripheral blood

Background Rituximab (RTX) induces more than 98% depletion of the CD20 +B cells in blood after a single injection, yet 35% to 50% of RA treated patients show a poor response to the therapy1. Despite the identification of many different biomarkers, mostly in the B cell compartment2, adequate prediction of response to RTX treatment is still quite challenging. Objectives To test the hypothesis that non-response to rituximab can be predicted by analysing B-cell receptor (BCR) repertoire characteristics before and shortly after rituximab therapy. Methods Paired peripheral blood (PB) samples and synovial tissue (ST) samples were available from a total of 21 patients before therapy with RTX, and at 4 and 16/24 weeks after treatment. Next-generation sequencing was used to analyse the BCR repertoire, and asses the frequency of high expanded clones (HECs:>0.5% of the sequenced reads)3 and load of somatic hypermutation (SHM). Clinical response was evaluated at 6 month following EULAR response criteria. Results In spite of the complete depletion of B cells (measured using CD19) with conventional flow cytometry, we detect a complete BCR repertoire at week 4 and 16/24 after RTX treatment. The post-treatment PB BCR repertoire is composed of fewer, but more expanded and more mutated clones compared to baseline (figure 1). Non-response associates with a higher number of HECs at week 4 (p Conclusions Incomplete depletion of the baseline BCR clonal repertoire in peripheral blood within the first month of treatment predicts poor clinical response at 6 months, revealing the persistence of “rituximab-resistant” BCR clonal signatures associated with treatment failure. In all patients the PB BCR repertoire at 4 weeks after rituximab is dominated by few but highly expanded and highly mutated BCR clones, most likely CD20-negative plasmablasts, while less pronounced and delayed effects are observed in the ST BCR repertoire. References [1] Cohen SB, et al. Arthritis Rheum2006;54:2793–806. [2] Benucci M, et al. Autoimmun Rev2010;9:801–3. [3] Doorenspleet ME, et al. Ann Rheum Dis2014;73:756–628. Disclosure of Interest None declared