Severe acute respiratory syndrome coronavirus-2, the causative agent of coronavirus disease 2019 (COVID-19), was declared a pandemic by the World Health Organization on 11th March 2020 and is a major global health concern. How to treat patients with COVID-19 effectively is a common question for physicians worldwide. According to recent statistical data released by the Chinese Government, approximately 19% of cases of COVID-19 are severe or critical.

Huang et al. reported the clinical features and cytokine profile of critically ill patients with COVID-19 in Wuhan, China, and suggested that a cytokine storm (ie higher concentrations of granulocyte-colony stimulating factor, interferon gamma-induced protein 10, monocyte chemoattractant protein 1, macrophage inflammatory protein 1α and tumour necrosis factor α) could be associated with the severity of disease [1]. Another study from China reported that increased expression of interleukin (IL)-2R and IL-6 in serum appears to predict the severity and prognosis of patients with COVID-19 [2]. Additionally, pathological examination of a biopsy sample from a patient who died from COVID-19 revealed interstitial mononuclear inflammatory infiltrates in both lungs, dominated by lymphocytes [3]. Furthermore, peripheral blood flow cytometric analysis showed that overactivation of T cells accounted, in part, for the severe immune injury in this