Unexpected better outcome in a liver transplant recipient with COVID-19: a beneficial effect of tacrolimus?

Coronavirus disease 2019 (COVID-19) is a serious respiratory illness caused by SARS-CoV-2. There is controversy about whether their immunosuppressive status is a risk factor or a protective factor for developing severe disease. We report herein the clinical outcome of three family members that had COVID-19 infection, presenting with and without different risk factors that have been described in more severe disease. Paradoxically, the patient with more risks of developing a severe disease, a 64-year-old woman, 2-years liver transplant recipient under treatment with tacrolimus, presented a similar outcome compared to the two other members of the family. She showed shorter hospitalization time, similar clinical outcome with fewer oxygen needs. The present clinical observation raises the question about the possible beneficial effect of tacrolimus in patients with COVID-19. Indeed, tacrolimus (FK-506) have an inhibitory effect on human coronaviruses by: 1) an antiviral effect by binding to the FK-506-binding proteins (FKBP) with a subsequent inhibition of their peptidyl-prolyl cis/trans isomerase (PPIase) activity, which seems to be important for the coronavirus life cycle; and 2) regulating the immune response by the inhibition of the activity of the nuclear factor of activated T-cells (NFAT) required for immunosuppression. The present observation states that liver recipients' patients with COVID-19 may not have worse outcomes when compared with other patients that have COVID-19 risk factors and puts in evidence the two mechanisms related to tacrolimus.