Distinct TCR repertoire in PIMS-TS/MIS-C patients: evidence for thymus involvement

During the COVID-19 pandemic a rare new paediatric inflammatory condition (paediatric inflammatory multisystem temporally associated with COVID-19 (PIMS-TS)/MIS-C) was identified which correlated with previous or recent SARS-CoV-2 infection. PIMS-TS led to severe multi-organ inflammation, suggestive of disruption of central tolerance and thymus function. Here we investigated the possible role of the thymus in paediatric PIMS-TS. We confirmed that human thymus explants can be infected with SARS-CoV-2 in vitro. Comparison of T-cell populations in blood from PIMS-TS patients and age-matched healthy control children showed that although the overall proportions of CD4 and CD8 T-cell populations were decreased in PIMS-TS patients, the proportion of naïve cells in the CD4 population was higher in the PIMS-TS group. In PIMS-TS patients, the number of TREC in PBMC correlated strongly with the proportion of naive CD4 and CD8 T-cells, whereas this correlation was not present in healthy children. Sequencing rearranged TCRbeta and TCRalpha transcripts from FACS- sorted CD4+CD8-CD3+ and CD4-CD8+CD3+ from blood from PIMS-TS, healthy children, and additionally paediatric severe COVID-19 patients, showed that while all three groups showed similar diversity and distribution, the repertoire of the PIMS-TS and COVID-19 groups had distinctive patterns of TCR gene segment usage and VJ combinatorial usage compared to healthy controls (TRBV11-2xTRBJ2-7, TRBV11-2xTRBJ1-1, TRBV11-2xTRBJ2-5, TRBV11- 2xTRBJ2-1; TRBV29-1xTRBJ2-7, TRBV29-1xTRBJ1-1 enriched in PIMS-TS; TRBV7-9xTRBJ1-2, TRAV9-2xTRAJ30 and TRAV26-1xTRAJ39 enriched in COVID-19). The non-productive TCR rearrangements in the PIMS-TS group were also enriched for TRBV11-2, and showed bias towards distal (5’TRAV to 3’TRAJ) TCRalpha gene segment usage, suggesting involvement of the thymus in PIMS-TS.

新冠大流行期间，一种罕见的新型儿童炎症性疾病——与新冠病毒时空相关的儿童多系统炎症综合征（paediatric inflammatory multisystem temporally associated with COVID-19, PIMS-TS）/儿童多系统炎症综合征（multisystem inflammatory syndrome in children, MIS-C）被发现，该疾病与既往或近期的严重急性呼吸综合征冠状病毒2型（SARS-CoV-2）感染相关。PIMS-TS可引发严重的多器官炎症，提示中枢免疫耐受及胸腺功能紊乱。本研究探讨了胸腺在儿童PIMS-TS中的潜在作用。我们证实，人胸腺外植体在体外可被SARS-CoV-2感染。对比PIMS-TS患者与年龄匹配的健康对照儿童的血液T细胞群体发现，尽管PIMS-TS患者的CD4和CD8 T细胞总体比例有所下降，但CD4群体中初始T细胞的比例在PIMS-TS组中更高。在PIMS-TS患者中，外周血单个核细胞（Peripheral Blood Mononuclear Cell, PBMC）中的T细胞受体切除环（T-cell receptor excision circles, TREC）数量与初始CD4和CD8 T细胞的比例呈显著相关，而这一相关性在健康儿童中并不存在。对来自PIMS-TS患者、健康儿童以及儿童重症新型冠状病毒肺炎患者的经荧光激活细胞分选（Fluorescence-Activated Cell Sorting, FACS）分选的CD4+CD8-CD3+和CD4-CD8+CD3+ T细胞的重排T细胞受体β（TCRβ）和T细胞受体α（TCRα）转录本进行测序，结果显示，尽管三组的多样性和分布相似，但与健康对照组相比，PIMS-TS组和新冠组的T细胞受体基因片段使用模式及VJ组合使用模式存在显著差异：PIMS-TS组富集TRBV11-2xTRBJ2-7、TRBV11-2xTRBJ1-1、TRBV11-2xTRBJ2-5、TRBV11-2xTRBJ2-1以及TRBV29-1xTRBJ2-7、TRBV29-1xTRBJ1-1；新冠组则富集TRBV7-9xTRBJ1-2、TRAV9-2xTRAJ30以及TRAV26-1xTRAJ39。PIMS-TS组的非功能性TCR重排同样富集TRBV11-2，且表现出向远端（5’端TRAV至3’端TRAJ）TCRα基因片段使用的偏好性，这提示胸腺参与了PIMS-TS的发病过程。