High CD4‐to‐CD8 ratio identifies an at‐risk population susceptible to lethal COVID‐19

Around half of people with severe COVID‐19 requiring intensive care unit (ICU) treatment will survive, but it is unclear how the immune response to SARS‐CoV‐2 differs between ICU patients that recover and those that do not. We conducted whole‐blood immunophenotyping of COVID‐19 patients upon admission to ICU and during their treatment and uncovered marked differences in their circulating immune cell subsets. At admission, patients who later succumbed to COVID‐19 had significantly lower frequencies of all memory CD8+ T cell subsets, resulting in increased CD4‐to‐CD8 T cell and neutrophil‐to‐CD8 T cell ratios. ROC and Kaplan‐Meier analyses demonstrated that both CD4‐to‐CD8 and neutrophil‐to‐CD8 ratios at admission were strong predictors of in‐ICU mortality. Therefore, we propose the use of the CD4‐to‐CD8 T cell ratio as a marker for the early identification of those individuals likely to require enhanced monitoring and/or pro‐active intervention in ICU.