Increased IL‐10‐producing regulatory T cells are characteristic of severe cases of COVID‐19

OBJECTIVES: The pandemic spread of the coronavirus SARS‐CoV‐2 is due, in part, to the immunological properties of the host–virus interaction. The clinical presentation varies from individual to individual, with asymptomatic carriers, mild‐to‐moderate‐presenting patients and severely affected patients. Variation in immune response to SARS‐CoV‐2 may underlie this clinical variation. METHODS: Using a high‐dimensional systems immunology platform, we have analysed the peripheral blood compartment of 6 healthy individuals, 23 mild‐to‐moderate and 20 severe COVID‐19 patients. RESULTS: We identify distinct immunological signatures in the peripheral blood of the mild‐to‐moderate and severe COVID‐19 patients, including T‐cell lymphopenia, more consistent with peripheral hypo‐ than hyper‐immune activation. Unique to the severe COVID‐19 cases was a large increase in the proportion of IL‐10‐secreting regulatory T cells, a lineage known to possess anti‐inflammatory properties in the lung. CONCLUSION: As IL‐10‐secreting regulatory T cells are known to possess anti‐inflammatory properties in the lung, their proportional increase could contribute to a more severe COVID‐19 phenotype. We openly provide annotated data (https://flowrepository.org/experiments/2713) with clinical correlates as a systems immunology resource for the COVID‐19 research community.