OP0242 SYNOVIAL TISSUE AND BLOOD DEEP B/T CELL PHENOTYPING EXPLAINS RESPONSE MECHANISMS TO RITUXIMAB IN RHEUMATOID ARTHRITIS IN R4RA (2024)

Abstract

Background: In the R4RA biopsy-driven randomized clinical trial[1] rheumatoid arthritis (RA) patients were randomised to rituximab or tocilizumab based on their synovial tissue B cell rich/poor signature. Response, defined as 50% improvement of clinical disease activity index (CDAI50), was assessed at 16 weeks. Samples from this cohort were utilised to improve understanding of pathogenic mechanisms determining response to rituximab. This is still a major issue with up to 5-20% of RA patients not responding to all current medication. While rituximab was designed to target CD20 on B cells, effects on CD4 T cells[2] and a highly inflammatory CD20dim T cell population[3] has been described. Several mechanisms of non-response have been proposed, including incomplete B cell depletion in synovium after rituximab.

Objectives: Investigate mechanisms of response and non-response to rituximab through deep molecular and cellular phenotyping of blood and synovial biopsies pre and post treatment.

Methods: B cell receptor (BCR) repertoires from synovial biopsies (n=9) and matched peripheral blood (n=7) RNA from RA patients at baseline and 16 weeks post rituximab were amplified and sequenced. Blood T and B cells (total n=39 baseline, n=33 post-rituximab) were phenotyped and quantified with a 27-marker panel on a spectral flow cytometer and matched with serum protein profiling (proteomics platform) and bulk RNA-Seq from blood pre- and post-rituximab.

Conclusion: Our results show that there may be multiple mechanisms explaining rituximab response including i) failure to deplete B cell clonotypes in the synovium, ii) higher NK-cell levels that may help clear rituximab-coated B cells and higher levels of inflammatory, CD20 targetable T cells, iii) higher activation profile in T cells preventing response and iv) a B cell profile skewed towards CD19 in non-responders and towards CD20 in responders in the blood. These findings enrich our understanding of mechanisms of response and non-response to rituximab, and could be used as biomarkers for patient stratification at baseline. We observed B cell repopulation originating from within synovium in all patients, which may also explain future relapse.

Acknowledgements: We thank all patients participating in the trial and the Patient Advisory Group. The R4RA trial was funded by the Efficacy and Mechanism Evaluation (EME) Programme, a partnership between the Medical Research Council (MRC) and the National Institute for Health and Care Research (NIHR) (grant no. 11/100/76), Versus Arthritis (Experimental Arthritis Treatment Centre, grant number 20022) and Barts Charity (grant number 523/819), MRC and Arthritis Research UK (ARUK) by joint funding of Maximizing Therapeutic Utility in Rheumatoid Arthritis (MATURA) (grant numbers MR/K015346/1 and 20670 respectively), NIHR (grant 131575) and MRC TRACT-RA (MR/V012509/1). This work acknowledges the support of the National Institute for Health Research Barts Biomedical Research Centre (NIHR 203330) as well as the Wellcome Trust for providing funding for the stipend (Wellcome Trust GMS stipend: BST00080.H508.01) for Lauren Overend.

Disclosure of Interests: Anna Surace: None declared, Lauren Overend: None declared, Elisabetta Sciacca: None declared, Liliane Fossati-Jimack: None declared, Edyta Jaworska: None declared, Elena Pontarini: None declared, Rachael J.M. Bashford-Rogers Co-founder of Alchemab Therapeutics Ltd, Alchemab Therapeutics Ltd and GSK, Costantino Pitzalis: None declared, Myles Lewis: None declared.