Polyphenolic Extract (PE) from Olive Oil Exerts a Potent Immunomodulatory Effect and Prevents Graft-versus-Host Disease in a Mouse Model

•Polyphenolic extract (PE) decreased activation, IL-2 and TNF-α secretion, and AKT-P and NF-κB in T cells.•A PE-supplemented diet decreased acute graft-versus-host disease risk and improved survival in a mice model.•A decrease in IL-2, IL-17, and TNF-α secretion was observed among mice receiving PE.•Feces butyrate concentration was higher in mice receiving PE after transplantation.