Alterations in the CD56 - and CD56 + T Cell Subsets during COVID-19.

The effectiveness of the antiviral immune response largely depends on the activation of cytotoxic T cells. The heterogeneous group of functionally active T cells expressing the CD56 molecule (NKT-like cells), that combines the properties of T lymphocytes and NK cells, is poorly studied in COVID-19. This work aimed to analyze the activation and differentiation of both circulating NKT-like cells and CD56 - T cells during COVID-19 among intensive care unit (ICU) patients, moderate severity (MS) patients, and convalescents. A decreased proportion of CD56 + T cells was found in ICU patients with fatal outcome. Severe COVID-19 was accompanied by a decrease in the proportion of CD8 + T cells, mainly due to the CD56 - cell death, and a redistribution of the NKT-like cell subset composition with a predominance of more differentiated cytotoxic CD8 + T cells. The differentiation process was accompanied by an increase in the proportions of KIR2DL2/3 + and NKp30 + cells in the CD56 + T cell subset of COVID-19 patients and convalescents. Decreased percentages of NKG2D + and NKG2A + cells and increased PD-1 and HLA-DR expression levels were found in both CD56 - and CD56 + T cells, and can be considered as indicators of COVID-19 progression. In the CD56 - T cell fraction, increased CD16 levels were observed in MS patients and in ICU patients with lethal outcome, suggesting a negative role for CD56 - CD16 + T cells in COVID-19. Overall, our findings suggest an antiviral role of CD56 + T cells in COVID-19.