Single cell RNA and TCR sequencing reveals substantive similarities between synovial fluid and synovial tissue T-cells in inflammatory arthritis.. Single cell RNA and TCR sequencing reveals substantive similarities between synovial fluid and synovial tissue T-cells in inflammatory arthritis.

Objective: Synovial fluid (SF) derived T-cells are frequently studied as a proxy for investigating the synovial tissue (ST) T-cell infiltrate in inflammatory arthritis. However, since ST is the primary site of inflammatory activity, there is debate as to whether SF provides a true reflection of the ST T-cell population. Methods: In this study, we used single cell RNA sequencing paired with single cell TCR sequencing to directly compare memory T-cells from paired samples of SF and ST from 6 patients with inflammatory arthritis to investigate their similarity in terms of T-cell receptor (TCR) repertoire and T-cell subset composition. Results: The TCR repertoires of SF and ST T-cells were strikingly similar, particularly for CD8+ T-cells. A median of 49% of the total CD8+ TCR repertoire in SF was shared with ST, compared to 20% shared with blood and 47% of the ST CD8+ TCR repertoire was shared with SF compared to 25% with blood. Furthermore, once the effect of collagenase digestion on gene expression by ST T-cells had been accounted for, the frequencies of specific CD8+ and CD4+ T-cell subsets were, in general, very similar in SF and ST and were distinct from blood. Conclusion: Our results suggest that T-cells migrate and equilibrate between SF and ST and maintain similar phenotypes in both sites. We conclude that SF is an appropriate proxy for investigating the T-cell infiltrate in inflamed synovium using single cell RNA sequencing, particularly in terms of investigating the TCR repertoire. Overall design: Single cell RNA and TCR sequencing analysis of memory T cells from blood, synovial fluid and synovial tissue from patients with psoriatic arthritis

研究目标：滑液（Synovial fluid, SF）来源的T细胞常被用作研究炎性关节炎患者滑膜组织（Synovial tissue, ST）T细胞浸润的替代模型。然而由于滑膜组织是炎症活动的主要部位，学界对于滑液能否真实反映滑膜组织的T细胞群体仍存在争议。
方法：本研究采用单细胞RNA测序（single cell RNA sequencing）联合单细胞T细胞受体（T-cell receptor, TCR）测序技术，对6名炎性关节炎患者的配对滑液、滑膜组织样本中的记忆性T细胞进行直接比较，以分析二者在TCR库（TCR repertoire）及T细胞亚群组成方面的相似性。
结果：滑液与滑膜组织的T细胞TCR库具有极高的相似性，尤以CD8+ T细胞为甚。滑液中总计49%的CD8+ TCR库可与滑膜组织共享，而仅有20%可与血液共享；滑膜组织中总计47%的CD8+ TCR库可与滑液共享，仅25%可与血液共享。此外，在校正了胶原酶消化对滑膜组织T细胞基因表达的影响后，特定CD8+及CD4+ T细胞亚群的频率在滑液与滑膜组织中整体极为相似，且二者均与血液中的亚群频率存在显著差异。
结论：本研究结果表明，T细胞可在滑液与滑膜组织之间迁移并达到平衡，且在两个部位维持相似的表型。据此我们认为，滑液可作为通过单细胞RNA测序研究炎性滑膜组织T细胞浸润的合适替代模型，尤其在TCR库相关研究中优势显著。
整体实验设计：对银屑病关节炎患者血液、滑液及滑膜组织中的记忆性T细胞进行单细胞RNA及TCR测序分析。