Significance Statement: There is no proven effective treatment for a major cause of graft failure, late antibody-mediated rejection, but IL-6, a cytokine known to promote B cell immunity, may be a promising therapeutic target. The authors describe the results of a phase 2 randomized clinical trial involving 20 patients, designed to evaluate the safety (primary endpoint) and efficacy (secondary endpoint analysis) of an anti–IL-6 antibody, clazakizumab, versus placebo in late antibody-mediated rejection. Although the occurrence of serious infections and diverticulitis presented important safety signals, clazakizumab was associated with an early decrease in donor-specific antibody levels, modulated antibody-mediated rejection activity, and slowed the decline of renal function. Preliminary efficacy results suggest a potentially beneficial effect of clazakizumab and may therefore support the design of larger trials with a longer duration of follow-up. Background: Late antibody-mediated rejection (ABMR) is a leading cause of transplant failure. Blocking IL-6 has been proposed as a promising therapeutic strategy. Methods: We performed a phase 2 randomized pilot trial to evaluate the safety (primary endpoint) and efficacy (secondary endpoint analysis) of the anti–IL-6 antibody clazakizumab in late ABMR. The trial included 20 kidney transplant recipients with donor-specific, antibody-positive ABMR ≥365 days post-transplantation. Patients were randomized 1:1 to receive 25 mg clazakizumab or placebo (4-weekly subcutaneous injections) for 12 weeks (part A), followed by a 40-week open-label extension (part B), during which time all participants received clazakizumab. Results: Five (25%) patients under active treatment developed serious infectious events, and two (10%) developed diverticular disease complications, leading to trial withdrawal. Those receiving clazakizumab displayed significantly decreased donor-specific antibodies and, on prolonged treatment, modulated rejection-related gene-expression patterns. In 18 patients, allograft biopsies after 51 weeks revealed a negative molecular ABMR score in seven (38.9%), disappearance of capillary C4d deposits in five (27.8%), and resolution of morphologic ABMR activity in four (22.2%). Although proteinuria remained stable, the mean eGFR decline during part A was slower with clazakizumab compared with placebo (−0.96; 95% confidence interval [95% CI], −1.96 to 0.03 versus −2.43; 95% CI, −3.40 to −1.46 ml/min per 1.73 m² per month, respectively, P=0.04). During part B, the slope of eGFR decline for patients who were switched from placebo to clazakizumab improved and no longer differed significantly from patients initially allocated to clazakizumab. Conclusions: Although safety data indicate the need for careful patient selection and monitoring, our preliminary efficacy results suggest a potentially beneficial effect of clazakizumab on ABMR activity and progression.

The non‐pathogenic and ubiquitous Torque Teno virus (TTV) is associated with immunosuppression in solid organ transplant recipients. Studies in kidney transplant patients proposed TTV quantification for risk stratification of graft rejection and infection. In this prospective trial (DRKS00012335) 386 consecutive kidney transplant recipients were subjected to longitudinal per‐protocol monitoring of plasma TTV load by PCR for 12 months post‐transplantation. TTV load peaked at the end of month 3 post‐transplantation and reached steady state thereafter. TTV load after the end of month 3 was analyzed in the context of subsequent rejection diagnosed by indication biopsy and infection within the first year post‐transplantation, respectively. Each log increase in TTV load decreased the odds for rejection by 22% (OR 0.78, 95%CI 0.62‐0.97; P=.027) and increased the odds for infection by 11% (OR 1.11, 95%CI 1.06‐1.15; P<.001). TTV was quantified at a median of 14 days before rejection was diagnosed and 27 days before onset of infection, respectively. We defined a TTV load between 1x10⁶ and 1x10⁸ copies/mL as optimal range to minimize the risk for rejection and infection. These data support the initiation of an interventional trial assessing the efficacy of TTV‐guided immunosuppression to reduce infection and graft rejection in kidney transplant recipients.

Background and objectives: In patients with kidney failure due to IgA nephropathy, IgA deposits can recur in a subsequent kidney transplant. The incidence, effect, and risk factors of IgA nephropathy recurrence is unclear, because most studies have been single center and sample sizes are relatively small. Design, setting, participants, & measurements: We performed a multicenter, international, retrospective study to determine the incidence, risk factors, and treatment response of recurrent IgA nephropathy after kidney transplantation. Data were collected from all consecutive patients with biopsy-proven IgA nephropathy transplanted between 2005 and 2015, across 16 “The Post-Transplant Glomerular Disease” study centers in Europe, North America, and South America. Results: Out of 504 transplant recipients with IgA nephropathy, recurrent IgA deposits were identified by kidney biopsy in 82 patients; cumulative incidence of recurrence was 23% at 15 years (95% confidence interval, 14 to 34). Multivariable Cox regression revealed a higher risk for recurrence of IgA deposits in patients with a pre-emptive kidney transplant (hazard ratio, 3.45; 95% confidence interval, 1.31 to 9.17) and in patients with preformed donor-specific antibodies (hazard ratio, 2.59; 95% confidence interval, 1.09 to 6.19). After kidney transplantation, development of de novo donor-specific antibodies was associated with subsequent higher risk of recurrence of IgA nephropathy (hazard ratio, 6.65; 95% confidence interval, 3.33 to 13.27). Immunosuppressive regimen was not associated with recurrent IgA nephropathy in multivariable analysis, including steroid use. Graft loss was higher in patients with recurrence of IgA nephropathy compared with patients without (hazard ratio, 3.69; 95% confidence interval, 2.04 to 6.66), resulting in 32% (95% confidence interval, 50 to 82) graft loss at 8 years after diagnosis of recurrence. Conclusions: In our international cohort, cumulative risk of IgA nephropathy recurrence increased after transplant and was associated with a 3.7-fold greater risk of graft loss.

Significance Statement: Gdf15, which encodes a signaling factor activated by oxidative stress, DNA damage, and proinflammatory cytokines, is upregulated in the human and mouse kidney within a few hours of ischemia-reperfusion injury. Using novel mouse strains, the authors mapped cellular sites of Gdf15 expression in normal and injured kidney and examined Gdf15’s role in ischemia-reperfusion injury. They showed that Gdf15 is expressed within hypoxic regions of the kidney and is predominantly activated within tubular epithelial cells at injury repair sites; loss of Gdf15 exacerbated injury, enhancing the inflammatory response. In an analysis of clinical data, they demonstrated that single nucleotide polymorphisms linked to lower circulating GDF15 levels associate with an increased incidence of biopsy-proven acute rejection. These findings point to modulating GDF15 levels in patients receiving kidney transplant as a possible therapeutic strategy. Background: Gdf15 encodes a TGF-β superfamily member that is rapidly activated in response to stress in multiple organ systems, including the kidney. However, there has been a lack of information about Gdf15 activity and effects in normal kidney and in AKI. Methods: We used genome editing to generate a Gdf15 ^nuGFP-CE mouse line, removing Gdf15 at the targeted allele, and enabling direct visualization and genetic modification of Gdf15-expressing cells. We extensively mapped Gdf15 expression in the normal kidney and following bilateral ischemia-reperfusion injury, and quantified and compared renal responses to ischemia-reperfusion injury in the presence and absence of GDF15. In addition, we analyzed single nucleotide polymorphism association data for GDF15 for associations with patient kidney transplant outcomes. Results: Gdf15 is normally expressed within aquaporin 1–positive cells of the S3 segment of the proximal tubule, aquaporin 1–negative cells of the thin descending limb of the loop of Henle, and principal cells of the collecting system. Gdf15 is rapidly upregulated within a few hours of bilateral ischemia-reperfusion injury at these sites and new sites of proximal tubule injury. Deficiency of Gdf15 exacerbated acute tubular injury and enhanced inflammatory responses. Analysis of clinical transplantation data linked low circulating levels of GDF15 to an increased incidence of biopsy-proven acute rejection. Conclusions: Gdf15 contributes to an early acting, renoprotective injury response, modifying immune cell actions. The data support further investigation in clinical model systems of the potential benefit from GDF15 administration in situations in which some level of tubular injury is inevitable, such as following a kidney transplant.

Recognition of non‐self‐structures on donor cells represents the main immunological barrier in solid organ transplantation. The Human Leucocyte Antigens (HLA) are considered the most important non‐self (allo‐) antigens in transplantation. Long‐term graft attrition is mainly caused by the formation of alloreactive antibodies that are directed against non‐self‐structures (i.e. epitopes) on cell surface proteins. Recently published data provided evidence for a similar importance of non‐HLA mismatches between donors and recipients in acute rejection as well as long‐term kidney allograft survival. These data suggest a broader concept of immunological non‐self that goes beyond HLA incompatibility and expands the current concept of polymorphic non‐self epitopes on cell surface molecules from HLA to non‐HLA targets. Amino acid substitutions caused by single nucleotide variants in protein coding genes or complete loss of gene expression represent the basis for polymorphic residues in both HLA and non‐HLA molecules. To better understand these novel insights in non‐HLA alloimmunity we will first review basic principles of the alloimmune response with a focus on the HLA epitope concept in donor‐specific antibody formation before discussing key publications on non‐HLA antibodies.

Late antibody-mediated rejection (ABMR) triggered by donor-specific antibodies (DSA) is a cardinal cause of kidney allograft dysfunction and loss. Diagnostic criteria for this rejection type are well established, but effective treatment remains a major challenge. Recent randomized controlled trials (RCT) have failed to demonstrate the efficacy of widely used therapies, such as rituximab plus intravenous immunoglobulin or proteasome inhibition (bortezomib), reinforcing a great need for new therapeutic concepts. One promising target in this context may be interleukin-6 (IL-6), a pleiotropic cytokine known to play an important role in inflammation and adaptive immunity. This investigator-driven RCT was designed to assess the safety and efficacy of clazakizumab, a genetically engineered humanized monoclonal antibody directed against IL-6. The study will include 20 DSA-positive kidney allograft recipients diagnosed with ABMR ≥ 365 days after transplantation. Participants will be recruited at two study sites in Austria and Germany (Medical University of Vienna; Charité University Medicine Berlin). First, patients will enter a three-month double-blind RCT (1,1 randomization, stratification according to ABMR phenotype and study site) and will receive either clazakizumab (subcutaneous administration of 25 mg in monthly intervals) or placebo. In a second open-label part of the trial (months 4–12), all patients will receive clazakizumab at 25 mg every month. The primary endpoint is safety and tolerability. Secondary endpoints are the pharmacokinetics and pharmacodynamics of clazakizumab, its effect on drug metabolism in the liver, DSA characteristics, morphological ABMR lesions and molecular gene expression patterns in three- and 12-month protocol biopsies, serum/urinary biomarkers of inflammation and endothelial activation/injury, Torque Teno viral load as a measure of overall immunosuppression, kidney function, urinary protein excretion, as well as transplant and patient survival. Currently, there is no treatment proven to be effective in halting the progression of late ABMR. Based on the hypothesis that antagonizing the effects of IL-6 improves the outcome of DSA-positive late ABMR by counteracting DSA-triggered inflammation and B cell/plasma cell-driven alloimmunity, we suggest that our trial has the potential to provide proof of concept of a novel treatment of this type of rejection. ClinicalTrials.gov, NCT03444103 . Registered on 23 February 2018 (retrospective registration).