# Distinctive T-cell receptor repertoire in paediatric inflammatory multisystem syndrome temporally associated with coronavirus disease 2019/multisystem inflammatory syndrome in children patients: possible thymus involvement

## TL;DR

This study found unique T-cell receptor patterns in children with a rare inflammatory condition linked to COVID-19, suggesting possible thymus dysfunction.

## Contribution

The study identifies distinctive TCR repertoire features in PIMS-TS patients, including novel patterns of gene segment usage and rearrangement biases.

## Key findings

- PIMS-TS patients showed higher proportions of naïve CD4 T cells and a strong correlation between TREC and naïve T cells.
- Distinct TCR gene segment usage patterns were observed in PIMS-TS and severe pediatric COVID-19 compared to healthy controls.
- Non-productive TCR rearrangements in PIMS-TS showed a bias toward 5′TRAV × 3′TRAJ gene segment usage, suggesting thymus involvement.

## Abstract

During the coronavirus disease 2019 (COVID-19) pandemic a rare new paediatric inflammatory condition (paediatric inflammatory multisystem syndrome 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 multiorgan 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 Peripheral blood mononuclear cells (PBMC) correlated strongly with the proportion of naïve CD4 and CD8 T cells, whereas this correlation was not present in healthy children. Sequencing rearranged TCRβ and TCRɑ 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 (TRBV11-2 × TRBJ2-7, TRBV11-2 × TRBJ1-1, TRBV11-2 × TRBJ2-5, TRBV11-2 × TRBJ2-1; TRBV29-1 × TRBJ2-7, TRBV29-1 × TRBJ1-1 enriched in PIMS-TS; TRBV7-9 × TRBJ1-2, TRAV9-2 × TRAJ30, and TRAV26-1 × TRAJ39 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) TCRɑ gene segment usage, suggesting involvement of the thymus in PIMS-TS.

Our study has identified distinctive characteristics of the TCR repertoires of children hospitalized with PIMS-TS. We found several similar features to previously described repertoires from PIMS-TS 2020 cohorts, as well as novel features of their TCR repertoires. Although our analyses do not definitively demonstrate thymus involvement in PIMS-TS, several aspects of these TCR repertoires are suggestive of thymus dysfunction, including changes in proportional combinatorial V × J usage in productive and non-productive TCR sequences with bias to 5′TRAV × 3′TRAJ rearrangements.

Graphical Abstract