Immune Checkpoint Receptor Expression Profiles of MAIT Cells in Moderate and Severe COVID-19

MAIT cells are one of the largest unconventional T cell populations and, recruited to the site of infection, play both protective and pathogenic roles during pulmonary viral infections. MAIT cell activation patterns change significantly during COVID-19, with a notable decrease in their frequency in peripheral blood of severe cases. In the present study, we aimed to investigate the expression profiles of various immune checkpoint pathways on MAIT, MAIT-like and non-MAIT cells in moderate and severe COVID-19 patients undergoing cytokine storm. Despite numerous studies comparing MAIT cell characteristics based on COVID-19 disease severity, none have delved into the critical differences in MAIT cell immune checkpoint profiles between moderate and severe COVID-19 patients, all experiencing a cytokine storm. Flow cytometry was used to analyse peripheral blood mononuclear cells from a cohort of 35 patients, comprising 18 moderate and 17 severe cases, alongside 14 healthy controls. Our investigation specifically focuses on severe COVID-19 presentations, revealing a marked deletion of MAIT cells. Further exploration into the regulatory dynamics of MAIT cell functionality reveals shifts in the expression profiles of critical immune checkpoint receptors, notably PD-1 and CD226. In severe COVID-19 patients, MAIT cells showed a significant decrease in the expression of CD226, whereas MAIT-like and non-MAIT cells demonstrated a significant increase in the expression of PD-1 compared to healthy individuals. The expression of the TIGIT receptor remained unaltered across all investigated groups. Our findings contribute to the existing knowledge by elucidating the changes in MAIT cell subpopulations and their potential role in COVID-19 disease severity.