Confirmation of Vβ21.3+ T cell expansion in French MIS-A cohort. (A and B) Frequency of total CD4+ and CD8+ T cells expressing the indicated Vβ chains in whole blood from A MIS-A patients and B control groups (COVID-19–associated myocarditis, post COVID-19 vaccination [BNT162b2 mRNA vaccine]–associated myocarditis, and flu-associated myocarditis), as measured by flow cytometry. Bubbles represent individual Vβ frequency shown as the standard deviation (SD) from reference mean (m) value for each Vβ subset in the general healthy adult population. Expansion is defined by a frequency greater than the reference mean plus 2 SD in healthy population. Data for 3 Vβ specificities are missing for MIS-A 12 (Vβ11, Vβ14, and Vβ22) and MIS-A 14 (Vβ9, Vβ16, and Vβ17) due to technical issues while performing the repertoire screening.