# Low CD3+ and CD4+ T cell levels predict need for ventilatory support and in-hospital mortality in patients with COVID-19: a retrospective cohort study

## TL;DR

Low levels of CD3+ and CD4+ T cells in hospitalized COVID-19 patients are linked to a higher risk of needing ventilatory support and dying in the hospital.

## Contribution

This study identifies CD3+ and CD4+ T cell counts as independent predictors of severe outcomes in hospitalized COVID-19 patients.

## Key findings

- CD3+ T cell levels below 666 cells/mm³ are associated with increased need for ventilatory support and in-hospital death.
- CD4+ T cell levels below 359 cells/mm³ are independently linked to in-hospital death.
- T-cell counts can help identify high-risk hospitalized COVID-19 patients.

## Abstract

The aim of the following study is to determine the association between lymphocyte subsets (total lymphocytes, CD3, CD4, CD8, B cells, NK cells) and clinical outcomes (need for non-invasive ventilatory support, ICU admission and in-hospital death) in patients hospitalized with SARS-CoV-2 infection.

We conducted a single-center, pre-vaccination, retrospective cohort study including adults hospitalized between March 2020 and April 2021. Peripheral blood samples were collected within the first 24 h of admission for immune phenotyping. Additional clinical data were obtained from electronic health records. Statistical analyses included chi-square tests and multivariable logistic regression, adjusted for clinical characteristics and inflammatory biomarkers. Optimal cutoff points for immune and inflammatory markers were determined using the Youden index.

Among 959 patients, 29.4% required ventilatory support, 11.3% required ICU admission, and 10.7% died. In multivariable analysis adjusted by clinical and laboratory confounders, CD3+ cells (cutoff point: 666 cells/mm3) were independently associated with ventilatory support (aOR: 2.3, 95%CI: 1.5–3.4, p = 0.013) and in-hospital death (aOR: 2.4, 95%CI: 1.3–4.3, p = 0.048); and CD4+ cells (cutoff point: 359 cells/mm3) were independently associated with in-hospital death (aOR: 2.8, 95%CI: 1.4–5.5, p = 0.045).

Adaptive immunity, especially T CD3+ and T CD4+ cells, is relevant in the prognosis of COVID-19, and T-cell counts can help identify hospitalized COVID-19 patients at risk for severe outcomes: ventilatory support and in-hospital death.