Polyclonal Vβ21.3 expansion in multisystem inflammatory syndrome in children despite SARS-CoV-2 vaccination
Authors' conclusion
In conclusion, breakthrough MIS-C patients presented with features consistent with unvaccinated MIS-C patients, including the hallmark Vβ21.3+ T cell expansion, indicating that prior immunisation with an mRNA vaccine targeting the Wuhan strain did not fully protect against MIS-C at the wave of a novel emerging variant early 2022.
Study context
- Population
- Children with breakthrough multisystem inflammatory syndrome in children (MIS-C) despite COVID-19 immunisation, hospitalised December 2021–April 2022 (100% male, 12.2–17.2 years)4 with blood samples
- Participants
- 5 vs 10
- Exposure
- Breakthrough MIS-C vs Vaccinated historical Kawasaki disease (KD)
- Breakthrough MIS-Cn = 5
- Vaccinated historical KDn = 10reference
- Outcome
- TCR Vβ21.3 skewing (Vβ21.3+ T cell expansion) in breakthrough MIS-C
Main finding
As reported in the abstract
Vβ21.3+ T cell expansion
- All 4 sampled patients presented with Vβ21.3+ T cell expansion, similar to MIS-C patients and in contrast to vaccinated historical KD patients
- The 2 patients with the earliest sampling post-illness had Vβ21.3+ T cell frequencies exceeding the reference mean value+10×SD
- Vβ21.3+ T cells showed increased surface expression of activation (HLA-DR, CD38) and exhaustion (PD-1, TIM-3) markers
Observational data: associations, not effects.
Original publication
Polyclonal Vβ21.3 expansion in multisystem inflammatory syndrome in children despite SARS-CoV-2 vaccination. RMD Open. Published 5 October 2025. doi:10.
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