Kidney transplant (KT) short-term outcomes have steadily improved over the last several decades, however, similar progress in long-term allograft survival has not yet been reached largely due to chronic allograft injury (CAI). In our previous funding cycle, we identified a gene expression signature in deceased donor kidney biopsies at pre-KT that was predictive of graft function, measured by eGFR, at 24-months post-KT. Further, our single- cell/nucleus transcriptome profiles yielded several important findings including that KT recipients with acute kidney injury have increased fibroblasts and macrophages (both donor- and recipient-origin) with a macrophage subset characterized by fibroblast-like markers; donor-derived macrophages were present in functioning kidney grafts with interstitial fibrosis and tubular atrophy (IFTA) more than 24-mo post-KT; and paired single-cell peripheral blood mononuclear cells (PBMCs) showed immune cell type specific profiles reflecting graft injury. Thus, our results revealed the unappreciated role of donor kidney cells (immune and non-immune) on tissue repair and local immunomodulation, which plays a critical role in response to injury and determines graft function. Moreover, post-KT graft survival is determined by a complex interplay between donor and recipient factors. Thus, our findings guided the establishment of our new hypothesis that early measurable donor and donor-recipient cellular interactions and molecular profiles are strong indicators of chronic inflammatory responses and maladaptive repair circuits, shaping long-term graft outcomes. Therefore, in this funding cycle, we will elucidate the effects of donor cell type-specific drivers of injury that exacerbate the initial donor/recipient immune- and non-immune cell interactions in response to injury and determine how these events are reflected in the peripheral samples, allowing non-invasive graft monitoring by using cell type-specific markers of injury. This will be accomplished by leveraging our large unique available resource that includes donor biopsies (pre-KT) with paired longitudinal recipient biopsies and PBMCs (post-KT) along with KT recipient clinical outcomes to pursue the following specific aims: Aim 1. Assess donor and recipient cells' origin, function, and interactions that play a role in graft injury. Aim 2. Uncover cell type-specific molecular signatures from peripheral immune cells derived from KT recipients at pre-implantation and longitudinally post-KT, reflecting immune risk status and kidney graft function. Aim 3. Establish a novel statistical method for developing a composite score using high-dimensional donor/recipient molecular and clinical/demographic variables to predict graft function. This study will provide (i) cell type-specific gene signatures and regulatory regions that control the transition between healthy and diseased kidney graft states, eventually guiding efforts to reprogram cells to promote repair after injury, (ii) ...