Low T cell counts could affect outcomes for COVID-19 patients

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A study recently published in Frontiers in Immunology has demonstrated that COVID-19 patients displaying more severe symptoms have significantly reduced T cell counts, suggesting that even those with non-severe cases are at high risk of deterioration.

While it is well known that T cells play a role in antiviral immunity, this was the first study to analyze the count and function of T cells and cytokines concentrations in COVID-19 patients. The researchers hope their discovery could lead to a new potential treatment route for the virus.

“We should pay more attention to T cell counts and their function, rather than respiratory function of patients,” explained study author Yongwen Chen (Third Military Medical University, Chongqing, China). “More urgent, early interventions may be required in patients with low T lymphocyte counts.”

In this study, researchers analyzed the T cell counts and cytokine concentrations in serum samples of 522 COVID-19 patients and 40 healthy controls. All patients had been admitted to one of two hospitals in Wuhan (China) between December 2019 and January 2020, and ages ranged between 5 days and 97 years old.

In almost all COVID-19 cases, they observed a significantly lower number of T cells. This led them to deduce that T cell counts were negatively correlated with the severity of the case. COVID-19 patients admitted to intensive care units had significantly lower T-cell counts than less severe cases, and patients over the age of 60 had the lowest number of T cells.

Additionally, upon discovering that COVID-19 patients had significantly higher concentrations of cytokines, The authors suggested that rather than directly attacking T cells, the COVID-19 virus triggers a cytokine storm, which then acts to drive down T cell numbers.

The researchers also measured the expression of T cell exhaustion markers in 14 COVID-19 cases and discovered that the surviving T cells in COVID-19 patients were not able to function at full capacity. T cell exhaustion leaves patients more vulnerable to secondary infection, suggesting that careful monitoring is needed for all patients.

This discovery suggests a potential role for drugs that recover T cell numbers and boost T cell function in treating COVID-19. The researchers proposed existing drugs such as Tocilizumab could be effective, but acknowledged further research is needed to investigate this in the context of coronavirus.

Regardless of the outcome of these future studies, these findings were important in aiding the development of a deeper understanding of this novel virus and have provided valuable information to suggest potential avenues for further research.

Sources: Chen Y, Diao B, Wang C et al. Reduction and functional exhaustion of t cells in patients with coronavirus disease 2019 (COVID-19). Front. Immunol. doi:10.3389/fimmu.2020.00827 (2020) (Epub ahead of print); www.eurekalert.org/emb_releases/2020-05/f-csa042320.php

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