0980: Expansion of Viral-Reactive CD8+ T cell Repertoire Stratified by Pathotype in New-onset ACPA+ Rheumatoid Arthritis

Background/Purpose: Development of Rheumatoid Arthritis (RA) is strongly associated with specific HLA-DRB1 genotypes and the HLA-DR antigen binding groove, the shared epitope. HLA-B*08 also increases risk of ACPA+ RA, and large numbers of CD8+, including granzyme K (GZMK)+ tissue-resident T cells (Trm), infiltrate RA synovial tissue (ST) in active, established RA. ST from DMARD-naïve patients can be classified into lymphomyeloid (LM), diffuse myeloid (DM) or pauci-immune (PI) “pathotypes”. While most T cell receptor (TCR) repertoire analysis focused on highly inflamed LM ST, TCR repertoires of DM and PI ST are poorly characterized.

Methods: We compared CD45+ antigen-presenting cells (APCs) and TCR repertoire in arthroscopic ST and paired peripheral blood (PB) from 9 recent-onset DMARD-naïve ACPA+ DM- or PI-pathotype RA patients with symptom duration up to 1 year, using single-cell(sc) RNA/TCR-sequencing (all except one HLA-DRB1*04:01 shared-epitope+). ST biopsies from 9 ACPA+ DM and 10 PI pathotyped RA patients were imaged using spatial transcriptomic profiling (5,101 genes, 10x Genomics).

Results: scRNAseq identified PB classical and non-classical monocytes, dendritic cells (DCs). In ST, myeloid DCs and macrophages were enriched in APC and lymphocyte-activation genes. In PI pathotype PB non-classical monocytes, ST myeloid DCs and macrophages were reduced compared to DM pathotype. CD4+ T cells had limited clonal expansion. The repertoire included public non-expanded viral-reactive clonotypes. Most memory CD8+ T cells expressed GZMB, GRZK or both. GZMK+GZMB+/- CD8+ T cell clones were moderately expanded and expressed Trm markers in ST, while GZMB+GZMK- CD8 clones were highly-expanded in PB. Grouping of lymphocyte interactions by paratope hotspots (GLIPH) identified cytomegalovirus (CMV) and Epstein-Barr virus (EBV)-reactive TCRs, which were GZMB+ in PB, and often shared in ST as GZMK+ Trm. CMV-reactive clonal expansion occurred in DM and PI pathotypes, restricted by HLA-A*02:01 and HLA-A*03:01 evenly across pathotypes. In contrast, EBV-reactive clonal expansion (GZMK+, HLA-B*08-restricted) was highly-enriched in the PI pathotype. Xenium spatial imaging in DM and PA ST identified small numbers of infiltrating GZMB+GZMK+/- CD8+ T cells and rare plasma cells. Besides larger macrophage infiltrates and expanded lining fibroblasts, PI T-cell infiltrates in DM were distinguished from PI pathotype by adjacent Clec9A+ DCs or type 1 interferon-induced CXCL11.

Conclusion: The data suggest strong CD8+ PB clonal expansion towards latent viruses and bystander ST infiltration in early ACPA+ RA of both pathotypes, but with HLA-B*08-restriction skewed to EBV-reactive Trm in PI. MHC class I genes may shape the CD8+ Trm repertoire, viral antigen presentation and ST pathology in RA.