Trained immunity is facilitated by T cell-induced CD40-TRAF6 signaling [ChIP-seq]

Trained immunity refers to epigenetic and metabolic changes in innate immune cells following exposure to inflammatory signals, leading to a heightened response to secondary stimuli. Although this innate immune memory contributes to host defense against infections, it can also have maladaptive consequences in a broad range of immune-driven conditions. During the past decade, we have gained an increasingly better understanding of the molecular regulation of trained immunity, but the role of adaptive immune cells in modulation of trained immunity remains largely unknown. Here, we show that T cell interactions contribute to the induction of trained immunity in monocytes and that this mediated by CD40-TRAF6 signaling. Specifically, we found that inhibiting CD40-TRAF6 signaling prevents the induction of functional, transcriptomic, metabolic and epigenetic changes associated with trained immunity. Apart from detailed in vitro studies, we inhibited CD40-TRAF6 signaling in vivo in myeloid cells in a murine heart transplantation model which resulted in prolonged allograft survival. When the animals were additionally treated with costimulatory blockade by CTLA4-Ig, we observed immunological tolerance to the graft. Combined, our study reveals that trained immunity induction is regulated by CD40-TRAF6 signaling between myeloid and adaptive immune cells, and that this signaling can be efficiently leveraged for therapeutic purposes.