Detection of mismatched human leukocyte antigens (HLA) by adaptive immune cells is considered as the main cause of transplant rejection, leading to either T-cell mediated rejection (TCMR) or antibody-mediated rejection (ABMR). This canonical view guided the successful development of immunosuppressive therapies and shaped the diagnostic Banff classification for kidney transplant rejection that is used in clinics worldwide. However, several Observations have recently emerged that question this dichotomization between TCMR and ABMR, related to heterogeneity in the serology, histology, and prognosis of the rejection phenotypes. In parallel, novel insights were obtained concerning the dynamics of donor-specific anti-HLA antibodies, the immunogenicity of donor-recipient non-HLA mismatches and the autoreactivity against self-antigens. Moreover, the potential of innate allorecognition was uncovered, as exemplified by natural killer cell-mediated microvascular inflammation through missing self, and by the emerging evidence on monocyte-driven allorecognition. In this review, we highlight the gaps in the current classification of rejection, provide an overview of the expanding insights into the mechanisms of allorecognition, and critically appraise how these could improve our understanding and clinical approach to kidney transplant rejection. We argue that consideration of the complex interplay of various allorecognition mechanisms can foster a more integrated view of kidney transplant rejection and can lead to improved risk stratification, targeted therapies and better outcome after kidney transplantation.
Copyright © 2021. Published by Elsevier Inc.