T cell maturation is significantly affected by SARS-CoV-2 infection.

BACKGROUND: COVID-19 is a respiratory tract infection caused by the new coronavirus SARS-CoV-2. An adequate T-cell response is essential not only for fighting disease but also for creation of immune memory. Thus, the present study aims to evaluate the T cells of patients with moderate, severe, and critical COVID-19 not only at the time of illness but also two months after diagnosis to observe whether changes in this compartment persist.

METHODS: In this study, 166 COVID-19 patients were stratified into moderate/severe and critical disease categories. The maturation and activation of T cells were evaluated through flow cytometry. In addition, Treg cells were analyzed.

RESULTS: Until 15 days after diagnosis, patients presented a reduction in absolute and relative T lymphocyte counts. After two months, in moderate/severe patients, the counts returned to a similar level as that of the control group. In convalescent patients who had a critical illness, absolute T lymphocyte values increased considerably. Patients with active disease did not show differentiation of T cells. Nonetheless, after two months, patients with critical COVID-19 showed a significant increase in CD4+ EMRA (CD45RA+ effector memory) T lymphocytes. Furthermore, COVID-19 patients showed delayed T cell activation and reduced CD8+ suppressor T cells even two months after diagnosis. A reduction in CD4+ Treg cells was also observed, and their numbers returned to a similar level as that of healthy controls in convalescent patients.

CONCLUSION: The results demonstrate that COVID-19 patients have a delayed activation and differentiation of T cells. In addition, these patients have a great reduction of T cells with a suppressor phenotype. This article is protected by copyright. All rights reserved.