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Background Cardiac allograft vasculopathy (CAV) is the major cause of late allograft loss following heart transplantation. CAV lesions contain alloreactive T cells that secrete IFN-γ, a vasculopathic cytokine, and occur more frequently in patients with donor specific antibody (DSA). Pathologic interactions between these immune effectors, representing cellular and humoral immunity, respectively, remain largely unexplored. Methods and Results We used human panel reactive antibody (PRA) to form membrane attack complexes (MAC) on allogeneic endothelial cells in vitro and in vivo. Rather than inducing cytolysis, MAC upregulated inflammatory genes, enhancing the capacity of EC to recruit and activate allogeneic IFN-γ-producing CD4+ T cells in a manner dependent upon activation of non-canonical NF-κB signaling. Non-canonical NF-κB signaling was detected in situ within EC both in renal biopsies from transplant patients with chronic antibody-mediated rejection and in PRA-treated human coronary artery xenografts in immunodeficient mice. Upon re-transplantation into immunodeficient hosts engrafted with human T cells, PRA-treated grafts recruited more IFN-γ-producing T cells and enhanced CAV lesion formation. Conclusions Alloantibody and complement deposition on graft EC activate non-canonical NF-κB signaling, initiating a pro-inflammatory gene program that enhances alloreactive T cell activation and development of CAV. Non-canonical NF-κB signaling in EC, observed in human allograft specimens and implicated in lesion pathogenesis, may represent a target for new pharmacotherapies to halt the progression of CAV.

Human graft endothelial cells (ECs) can act as antigen-presenting cells to initiate allograft rejection by host memory T cells. Rapamycin, an mTOR inhibitor used clinically to suppress T cell responses, also acts on DCs, rendering them tolerogenic. Here, we report the effects of rapamycin on EC alloimmunogenicity. Compared with mock-treated cells, rapamycin-pretreated human ECs (rapa-ECs) stimulated less proliferation and cytokine secretion from allogeneic CD4 + memory cells, an effect mimicked by shRNA knockdown of mTOR or raptor in ECs. The effects of rapamycin persisted for several days and were linked to upregulation of the inhibitory molecules PD-L1 and PD-L2 on rapa-ECs. Additionally, rapa-ECs produced lower levels of the inflammatory cytokine IL-6. CD4 + memory cells activated by allogeneic rapa-ECs became hyporesponsive to restimulation in an alloantigen-specific manner and contained higher percentages of suppressive CD4 + CD25 hi CD127 lo FoxP3 + cells that did not produce effector cytokines. In a human-mouse chimeric model of allograft rejection, rapamycin pretreatment of human arterial allografts increased graft EC expression of PD-L1 and PD-L2 and reduced subsequent infiltration of allogeneic effector T cells into the artery intima and intimal expansion. Preoperative conditioning of allograft ECs with rapamycin could potentially reduce immune-mediated rejection.

We hypothesized that de novo donor-specific antibody (DSA) causes complement-dependent endothelial cell injury in kidney transplants, as assessed by expression of endothelial cell-associated transcripts (ENDATs), that may be attenuated through complement inhibition. In total, 15 participants (five control, 10 treatment) with DSA and deteriorating renal function were enrolled. The treatment group received 6 mo of eculizumab followed by 6 mo of observation, whereas controls were observed. The primary end point was percentage change in estimated GFR (eGFR) trajectory over the treatment period. The treatment group had an improved eGFR trajectory versus control, based on our predetermined two-sided 0.10 significance level (p = 0.09). Within-subject analysis of treated participants at 6-mo intervals did not show significant change (p = 0.60). Modeling C1q status showed that C1q-positive patients had significantly higher mean eGFR than patients with negative C1q (p = 0.04). Biopsies revealed elevated renal ENDATs in most participants, but ENDATs were not reduced with complement inhibition. Our data suggest that eculizumab treatment may stabilize kidney function in patients with chronic persistent DSA based on our pilot a priori significance threshold. ENDAT expression predicative of acute humoral injury is not reduced with complement inhibition in this chronic setting. Further studies will be necessary to determine which patients may benefit from eculizumab.

Inactive patients on the kidney transplant wait-list have a higher mortality. The implications of this status change on transplant outcomes between racial/ethnic groups are unknown.OBJECTIVES To determine if activity status changes differ among races/ethnicities and levels of sensitization, and if these differences are associated with transplant probability after implementation of the Kidney Allocation System. DESIGN, SETTING, AND PARTICIPANTSA multistate model was constructed from the Organ Procurement and Transplantation Network kidney transplant database (December 4, 2014, to September 8, 2016. The time interval followed Kidney Allocation System implementation and provided at least 1-year follow-up for all patients. The model calculated probabilities between active and inactive status and the following competing risk outcomes: living donor transplant, deceased donor transplant, and death/other. This retrospective cohort study included 42 558 patients on the Organ Procurement and Transplantation Network kidney transplant wait-list following Kidney Allocation System implementation. To rule out time-varying confounding from relisting, analysis was limited to first-time registrants. Owing to variations in listing practices, primary center listing data were used for dually listed patients. Individuals listed for another organ or pancreatic islets were excluded. Analysis began July 2017. MAIN OUTCOME AND MEASURESProbabilities were determined for transitions between active and inactive status and the following outcome states: active to living donor transplant, active to deceased donor transplant, active to death/other, inactive to living donor transplant, inactive to deceased donor transplant, and inactive to death/other. RESULTSThe median (interquartile range) age at listing was 55.0 (18.0-89.0) years, and 26 535 of 42 558 (62.4%) were men. White individuals were 43.3% (n = 18 417) of wait-listed patients, while black and Hispanic individuals made up 27.8% (n = 11 837) and 19.5% (n = 8296), respectively. Patients in the calculated plasma reactive antibody categories of 0% or 1% to 79% showed no statistically significant difference in transplant probability among races/ethnicities. White individuals had an advantage in transplant probability over black individuals in calculated plasma reactive antibody categories of 80% to 89% (hazard ratio [HR], 1.8 [95% CI, 1.4-2.2]) and 90% or higher (HR, 2.4 [95% CI, 2.1-2.6]), while Hispanic individuals had an advantage over black individuals in the calculated plasma reactive antibody group of 90% or higher (HR, 2.5 [95% CI, 2.1-2.8]). Once on the inactive list, white individuals were more likely than Hispanic individuals (HR, 1.2 [95% CI, 1.17-1.3]) or black individuals (HR, 1.4 [95% CI, 1.3-1.4]) to resolve issues for inactivity resulting in activation. CONCLUSIONS AND RELEVANCEFor patients who are highly sensitized, there continues to be less access to kidney transplant in the black population after the implementation of the Kidney Allocation System. Health disparities conti...