Background: Of all approved biologic therapies, other than anti-CD20-mediated lymphocyte depletion, only CTLA4-Ig/abatacept treatment reduces pathologic circulating pathological autoantibodies and provides clinical benefits. Yet, the underlying mechanism(s) remain poorly understood.

Objectives: Herein, our primary goal has been to elucidate the effect of co-stimulatory blockade on the representation of lymphocytes in the blood of RA patients and determine if there are shifts in B-cell disease associated B cell subsets and clonal dynamics associated with clinical response in the open-label RA and m emory B cells (RAMBA) trial.

Methods: Biologic-naïve patients, or those with remote exposure to TNFi, with seropositive RA, were enrolled and received the standard IV regimen of abatacept for 6 months. Clinical evaluation and biospecimen collection were performed at baseline, 3, 6, and 9 months or when a flare occurred. In addition to routine clinical lab testing, autoantibody responses were evaluated in a multiplex assay with IgM-RF, and citrullinated protein antigens, including CCP3. PBMCs or samples of negatively selected B-lineage cells were interrogated at a single cell level for high-dimensional surface phenotype and transcriptomic profiles, by E xpanded C ellular I ndexing of T ranscriptomes and E pitopes (eCITE) sequencing.

Results: 16/18 seropositive RA patients that completed standard abatacept treatment for 5 months, had complete clinical responses based on CDAI that were mirrored by reductions in serum RF and ACPA levels (not shown). Single-cell analyses of 7 patients demonstrated treatment-induced increases in naïve CD4+ T cells and reductions in regulatory T cells, and CD8+ effector memory cells (Figure 1 and 2 and not shown). CD19+ B-lineage cells were resolved into 9 subsets (Figure 1). Treatment was also associated with significant reductions of CD19+ sIgD-CD27- (DN2) B cells, CD19+CD69+IgM+IgD+ activated Naïve (aNav) B cells and antibody-secreting cells (ASC) that are linked to autoimmune B-cell responses (not shown). In the subject with the greatest number of identified single CD19+ B cells, antibody gene analysis demonstrated a remarkable expansion of a unique B-cell clonotypic set, with identical paired VH and VL rearrangements found in 21 different B cells, distributed across IgM+IgD- pre-switch memory, CD69+IgM+IgD+ activated naïve (aNav) and CD27-CD11c+Tbet+ DN2 detected across all four sampled timepoints. Most of these clonotypic B cells were identified as preswitch memory, which was numerically greatest at baseline, then decreased after 3 and 6 months of therapy, and then expanded at the time of the flare. These were absent in the transitional, naïve, post-switch DN1 and DN4 subsets and ASC. The identical VH rearrangements were closest to the VH3-33*04 DH6-13*01 and JH3*02, with 7 silent and 6 replacement (including a single CDR) mutation. The Vk region was closest to the Vk3-15*01 and Jk1*01 with 1 silent and 5 replacement (including a single CDR) mutations. As a recombinant IgM antibody, there was strong binding to the CCP3 peptide used for clinical diagnosis, citrullinated α-enolase, as well autoreactivity for nucleosome and Sm antigen, reflecting the broad breach in clonal immune tolerance.

Conclusion: Complete clinical response in RA to abatacept was associated with quantitative increases in naive CD4+ T cells, and reductions in extrafollicular activated naive, DN2, preswitch memory, and antibody-secreting cells (ASC). There were concurrent reductions in B-cell clonotypic expansions in these subsets, as identified by surface phenotype and transcriptomic profiles. Our findings are consistent with abatacept causing preferential therapeutic effects involving extrafollicular B cells, DN2 cells, which may arise in inflammation-associated ectopic lymphoid tissue, recently implicated as major RA-associated autoantibody producers in rheumatoid joints.

REFERENCES: NIL.

Acknowledgements: Supported in part by an unrestricted gift from BMS.

Disclosure of Interests: Gregg Silverman Genentech, GSK, Genentech, BMS, Novartis, William Rigby BMS, Jasmine Shwetar: None declared, Sladjana Skopelja-Gardner: None declared, Abhimanyu Amarnani: None declared, Kelly Ruggles: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.