KIR3DL1 and COVID-19: The comparison of KIR genes and KIR–HLA ligand combinations between Sardinian COVID-19 patients and Sardinian bone marrow donors have shown an overall increased frequency of KIR inhibitory genes in patients, with a statistically significant increase in KIR2DL1 and 2DL3, correlating them with increased susceptibility to SARS-CoV-2 infection.