A study of 76 severe COVID‑19 patients in Wuhan found that giving the peptide thymosin‑alpha‑1 lowered death rates and helped bring back low T‑cell numbers, especially in older people and those with very low CD4 or CD8 counts. It also reduced markers of exhausted T‑cells, suggesting a healthier immune response.

Thymosin alpha 1 (Tα1) had been used in the treatment of viral infections as an immune response modifier for many years. However, clinical benefits and the mechanism of Tα1 treatment for COVID-19 patients are still unclear. We retrospectively reviewed the clinical outcomes of 76 severe COVID-19 cases admitted to 2 hospitals in Wuhan, China, from December 2019 to March 2020. The thymus output in peripheral blood mononuclear cells from COVID-19 patients was measured by T-cell receptor excision circles (TRECs). The levels of T-cell exhaustion markers programmed death-1 (PD-1) and T-cell immunoglobulin and mucin domain protein 3 (Tim-3) on CD8+ T cells were detected by flow cytometry. Compared with the untreated group, Tα1 treatment significantly reduced the mortality of severe COVID-19 patients (11.11% vs 30.00%, P = .044). Tα1 enhanced blood T-cell numbers in COVID-19 patients with severe lymphocytopenia. Under such conditions, Tα1 also successfully restored CD8+ and CD4+ T-cell numbers in elderly patients. Meanwhile, Tα1 reduced PD-1 and Tim-3 expression on CD8+ T cells from severe COVID-19 patients compared with untreated cases. It is of note that restoration of lymphocytopenia and acute exhaustion of T cells were roughly parallel to the rise of TRECs. Tα1 treatment significantly reduced mortality of severe COVID-19 patients. COVID-19 patients with counts of CD8+ T cells or CD4+ T cells in circulation less than 400/μL or 650/μL, respectively, gained more benefits from Tα1. Tα1 reversed T-cell exhaustion and recovered immune reconstitution through promoting thymus output during severe acute respiratory syndrome-coronavirus 2 infection.