Tregs of non‐survivor COVID‐19 patients presented reduced frequencies of IL‐10 and TNF production. PBMCs and BAL cells from patients with severe COVID‐19 were incubated for 12 h in the presence of BFA without stimulation. Frequency of IL‐10 (a–d) and TNF (e–h) were evaluated by flow cytometry. Representative dot plots of Tregs producing IL‐10 on Day 7 (a, c) or TNF on Day 1 (e, f). Frequency of cytokine production by survivors (open circles) n = 9 (D1), n = 4 or 6 (D3) and n = 6 (D7) and non‐survivors (grey triangles) n = 10 (D1), n = 8 (D3) and n = 8 (D7) are represented by geometric means represented by horizontal lines (b, d, f and h). Differences between severe COVID‐19 groups were analysed by Mann–Whitney test and are indicated by asterisks (*) when statistically significant (p < 0.05). BAL, broncho‐alveolar aspirate; PBMC, peripheral blood mononuclear cell.