Updated project metadata. Myeloid-derived suppressor cells (MDSCs) have the capacity to suppress T cell-mediated immune responses, and impact clinical outcome of cancer, infections and transplantation settings. Although MDSCs were initially described as bone-marrow-derived immature myeloid cells (either monocytic [m-MDSC] or granulocytic [g-MDSC]), also mature neutrophils have been shown to exert MDSC activity towards T cells, in ways that so far remained unclear. In this study, we demonstrate that human neutrophils – both from healthy donors and cancer patients – do not exert MDSC activity unless they are activated. Using neutrophils with genetically well-defined defects, we found that reactive oxygen species (ROS) and granule-derived constituents are required for MDSC activity after direct CD11b-dependent neutrophil-T cell interactions. Besides these cellular interactions, neutrophils were engaged in the uptake of pieces of T cell membrane, a process called trogocytosis. Together, these interactions led to changes in T cell morphology, mitochondrial dysfunction and ATP depletion, as indicated by electron microscopy, mass spectrometry and metabolic parameters. Our studies characterize the different steps by which activated mature neutrophils induce functional T cell non-responsiveness and irreparable cell damage.