In this context, the clinical trial “HLA-G Immuno-Inhibitor Checkpoint Study in Patients With COVID-19 Infection: Molecular and Cellular Assessment (HLA-G-COVID) (NCT04613297)” has been started to evaluate the clinical significance of HLA-G and receptors ILT-2 expression on CD4+ and CD8+ lymphocytes, and the levels of peripheral sHLA-G and plasma HLA-G-bearing microvesicles among COVID-19 uninfected patients, non-hospitalized COVID-19 infected patients and hospitalized COVID-19 infected patients. Here, CD4 is linked to COVID-19.