Thus, the in-vivo results we obtained in the MA20 model, together with our observation that FasL is significantly increased in the BALF of critically-ill COVID-19 patients, provides a causal connection between FasL and severe COVID-19 and, at the same time, uncovers the translational potential of FasL blockade as a novel treatment for severe COVID-19. The gene discussed is FASLG; the disease is COVID-19.