Resident memory T cells form during persistent antigen exposure leading to allograft rejection.

Memories of rejection: Long-term graft survival after organ transplantation can be hindered by immune-mediated allograft rejection; thus, understanding these immune responses is crucial to developing new transplant-supporting therapies. Tissue-resident memory T cells (T_RM), a subset of memory T cells that reside in barrier tissues and do not recirculate, are detectable in transplanted organs, but it is unclear if they contribute to allograft rejection. Abou-Daya et al. created a mouse model of T cell–mediated kidney transplant rejection, showing that adoptively transferred, kidney antigen–specific effector T cells differentiated into functional, nonrecirculating antigen-specific T_RM in the transplanted kidneys. These kidney antigen–specific T_RM induced allograft rejection. These data suggest that T_RM in transplanted allografts can contribute to rejection and that targeting alloreactive T_RM might improve long-term graft survival in transplant recipients. Tissue-resident memory T cells (T_RM) contained at sites of previous infection provide local protection against reinfection. Whether they form and function in organ transplants where cognate antigen persists is unclear. This is a key question in transplantation as T cells are detected long term in allografts, but it is not known whether they are exhausted or are functional memory T cells. Using a mouse model of kidney transplantation, we showed that antigen-specific and polyclonal effector T cells differentiated in the graft into T_RM and subsequently caused allograft rejection. T_RM identity was established by surface phenotype, transcriptional profile, and inability to recirculate in parabiosis and retransplantation experiments. Graft T_RM proliferated locally, produced interferon-γ upon restimulation, and their in vivo depletion attenuated rejection. The vast majority of antigen-specific and polyclonal T_RM lacked phenotypic and transcriptional exhaustion markers. Single-cell analysis of graft T cells early and late after transplantation identified a transcriptional program associated with transition to the tissue-resident state that could serve as a platform for the discovery of therapeutic targets. Thus, recipient effector T cells differentiate into functional graft T_RM that maintain rejection locally. Targeting these T_RM could improve renal transplant outcomes. [ABSTRACT FROM AUTHOR]