A previous study revealed that monocytes in severe COVID-19 cases have the capacity to engage with CD8+ T cells, B cells and CD4+ T cells, chemokine receptors were also enriched in monocytes from severe patients.443 Chemokines interact with chemokine receptors to exert their biological effects, suggesting that these cytokines or their receptors could be potential treatments for severe COVID-19 patients and may become therapeutic targets for COVID-19 patients. Here, CD4 is linked to COVID-19.