In 2022, Beserra et al. [16] analysed sPD-1 and sPD-L1 in the serum of patients with COVID-19 and found similar levels of sPD-1 across groups, while sPD-L1 levels were elevated in patients with severe and critical symptoms relative to healthy controls, suggesting a relationship between sPD-L1 and COVID-19 severity. This evidence concerns the gene HOXD13 and COVID-19.