Association of lymphocyte subsets with mortality in severe COVID-19 pneumonia patients

Few studies have investigated the alterations in the T and B cell counts and related subgroups in pulmonary infections especially COVID-19. Here, we aimed to evaluate total T and B lymphocytes and T cell subgroup counts to find the possible correlation between number of these cells and severity and mortality in COVID-19 patients.

This study was performed on 40 patients with severe COVID-19 infection confirmed by reverse transcription-polymerase chain reaction (RT-PCR) and chest HRCT in August 2020. By the time of admission, T lymphocytes profile in peripheral blood was investigated using multicolor flow cytometry. The total number of T lymphocytes, CD4+ T cells, CD8+ T cells, and B lymphocytes were calculated. Expression of CD2, CD3, CD5, and CD7 as pan T cell surface markers and expression of CD38 and HLA-DR as activated markers on T lymphocytes were also evaluated.

Nine patients (22.5%) died during the study and 16 patients (40%) were admitted to ICU. Deceased patients demonstrated lower amounts of T cell count and CD4+ T cell count (with a marginal difference (p = 0.07)) compared with survived patients at the time of admission. The chance of mortality was significantly higher for patients with CD7 loss (OR = 14.89). A marginally significant relationship was also indicated between CD4<200/ml and mortality (OR = 8.65), but no other significant relationships were observed between variables and ICU admission.

Altogether, CD7 loss on T lymphocytes and CD4+ T cell count below 200/ml revealed a significant relationship with mortality. Considering T lymphocytes and T cell subgroup count could have a predictive value for patients suffering from COVID-19.