Polyclonal expansion of TCR VBETA 21.3+ CD4+ and CD8+ T CELLS is a hallmark of multisystem inflammatory syndrome in children

ABSTRACT

Introduction: At the end of April 2020, European clinicians warned the Public Health Agencies about an abnormal increase of Kawasakilike diseases and myocarditis requiring critical care support in the context of the ongoing COVID-19 epidemic in children. American clinicians also reported a large outbreak of severe inflammation in children following COVID-19 infection, a condition that is now named Pediatric Inflammatory Multisystemic Syndrome (PIMS) or Multisystem Inflammatory Syndrome in children (MIS-C). Objectives: As MIS-C combines clinical features of Kawasaki disease (KD) and Toxic Shock Syndrome (TSS), we aimed to compare the immunological profile of pediatric patients with these different conditions. Methods: We analysed blood cytokine expression, and the T cell repertoire and phenotype in 36 MIS-C cases, which were compared to 16 KD, 58 TSS, and 42 COVID-19 cases. Results: We observed an increase of serum inflammatory cytokines (IL-6, IL-10, IL-18, TNF-a, IFNg, CD25s, MCP1, IL-1RA) in MIS-C, TSS and KD, contrasting with low expression of HLA-DR in monocytes. We detected a specific expansion of activated T cells expressing the Vβ21.3 T cell receptor β chain variable region in both CD4 and CD8 subsets in 75% of MIS-C patients and not in any patient with TSS, KD, or acute COVID-19;this correlated with the cytokine storm detected. The T cell repertoire returned to baseline within weeks after MIS-C resolution. Vβ21.3+ T cells from MIS-C patients expressed high levels of HLA-DR, CD38 and CX3CR1 but had weak responses to SARS-CoV- 2 peptides in vitro. Consistently, the T cell expansion was not associated with specific classical HLA alleles. Conclusion: Thus, our data suggested that MIS-C is characterized by a polyclonal Vβ21.3 T cell expansion not directed against SARS-CoV-2 antigenic peptides, which is not seen in KD, TSS and acute COVID-19.