Elevated frequencies of CD14(+)HLA-DR(lo/neg) MDSCs in COVID-19 patients

Background: The immune responses, hyper-inflammation or immunosuppression, may be closely related to COVID-19 progression. We aimed to evaluate the changes of frequency of CD14(+)HLA-DR(lo/neg) MDSCs, a population of cells with potent immunosuppressive capacity, in COVID-19 patients. Methods: The levels of CD14(+)HLA-DR(lo/neg) MDSCs were determined by flow cytometry in 27 COVID-19 patients, and their association with clinical characteristics and laboratory data were analyzed. Results: The frequency of CD14(+)HLA-DR(lo/neg) MDSCs was elevated in COVID-19 patients, particularly severe patients. A follow-up comparison revealed a decline of CD14(+)HLA-DR(lo/neg) MDSCs percentages in most patients 1 day after testing negative for SARS-CoV-2 nucleic acid, but the levels of CD14(+)HLA-DR(lo/neg) MDSCs were still greater than 50.0% in 3 ICU patients 4-10 days after negative SARS-CoV-2 results. Elevated frequency of CD14(+)HLA-DR(lo/neg) MDSCs was positively correlated with oropharyngeal viral loads and length of hospital stay, while negatively correlated with lymphocyte counts and serum albumin. Moreover, strong correlations were observed between the frequency of CD14(+)HLA-DR(lo/neg) MDSCs and T cell subsets, NK cell counts, and B cell percentages. The frequency of CD14(+)HLA-DR(lo/neg) MDSCs could be used as a predictor of COVID-19 severity. Conclusions: A high frequency of CD14(+)HLA-DR(lo/neg) MDSCs, especially in severe patients, may indicate an immunoparalysis status and could be a predictor of disease severity and prognosis.