Increased PD-L1 Expression May Be Associated With the Cytokine Storm and CD8+ T-Cell Exhaustion in Severe COVID-19
Jiezhong Chen, Luis Vitetta
Abstract
To the Editor-Severe coronavirus disease 2019 is characterized by both a cytokine storm and lymphopenia with reduced frequency of CD4 + and CD8 + T cells [1]. CD8 + cytotoxic T-lymphocyte cells play a key role in virus clearance, thereby decreasing viral replication and viral load [2]. Numerous clinical studies have characterized the changes in CD8 + T cells in mild and severe COVID-19 patients that expose the importance of CD8 + T cells in the progression of COVID-19. However, the mechanisms by which the changes in CD8 + T cells that ensue are not well elucidated. The study by Vitte et al found that increased programmed death ligand-1 (PD-L1) in basophils, eosinophils, monocytes, and natural killer cells in severe COVID-19 patients, particularly the expression of PD-L1 in basophils and eosinophils, were correlated with COVID-19 severity [3]. These findings could provide a plausible explanation for CD8 + T-cell exhaustion in COVID-19.