Prevention, diagnosis and treatment of antibody-mediated rejection
Emerging evidence suggests antibody-mediated rejection as the leading cause of late kidney transplant loss. We aim to develop novel diagnostic tools and treatment options to counteract the deleterious effects of humoral transplant injury.
Even though antibody-mediated graft damage has been recognized as one of the leading causes of late kidney transplant failure, there is still no established treatment and methods for timely and reliable prediction of humoral injury are still to be established. A major focus of ongoing studies is the refinement of desensitization strategies in HLA antibody-incompatible transplantation and the evaluation of novel treatment strategies to counteract chronic antibody-mediated rejection processes. In addition, our current projects aim at optimizing pre- and post-transplant screening tools for assessing individual risks of early and late antibody mediated allograft rejection.
A major interest of VIETAC is the evaluation of innovative ‚anti-humoral‘ strategies in prospective clinical trials:
The BORTEJECT study (sponsored by the Austrian Science Fund; clinicaltrials.gov, NCT01873157) is a randomized placebo-controlled trial to evaluate the effect of the proteasome inhibitor Bortezomib on transplant outcomes in patients with late antibody-mediated rejection (ABMR; October 2013 – February 2017). Patient screening (cross-sectional DSA monitoring of more than 700 recipients with ≥6 months allograft function) has been completed in February 2015. According to the study protocol, 44 DSA-positive kidney transplant recipients with histomorphological and/or immunohistochemical signs of AMR in protocol biopsies have been included. The primary endpoint is the slope of (calculated glomerular filtration rate) eGFR trajectories over 24 months (study powered to detect a 5 mL difference in eGFR between placebo and Bortezomib). In the context of this interventional trial, we have built up a cooperation with Dr. Philip Halloran, director of the Alberta Transplant Applied Genomics Center ‚ATAGC’ in Edmonton, Alberta, Canada to assess ABMR-related scoring of molecular signatures from our biopsy material on microarray based technology.
In tight cooperation with TrueNorth Therapeutics Inc. (South San Francisco, USA; www.truenorthrx.com) and the Department of Clinical Pharmacology (Medical University of Vienna), we are investigating the effect of anti-C1s monoclonal antibody TNT009 on HLA antibody-triggered classic pathway activation, both in pre-clinical experimental studies and a phase 1 trial in healthy volunteers and patients with late ABMR.
Desensitization and crossmatch-conversion of sensitized recipients of a deceased donor kidney allograft
Donor specific HLA antibodies (DSA) prior to transplantation are associated with positive complement dependent cytotoxicity crossmatch (CDCXM), antibody-mediated rejection (ABMR) and inferior allograft survival. Strategies to overcome immunological barriers are a major interest of our study group.
A primary focus of our study group is the development of desensitization strategies in HLA antibody-incompatible deceased donor transplantation. At our unit, sensitized patients (since 2009 prospective solid-phase monitoring for preformed DSA) are subjected to a protocol of peri-transplant IA (initiation of the program in the 1990ies) to counteract the deleterious effects of preformed DSA, with or without a positive CDCXM. In a recent study we studied a cohort of 101 DSA and/or crossmatch-positive recipients who had been subjected to this protocol between 2009 and 2013. In an effort to establish a tailored approach of treatment allocation, we evaluated clinical intermediate-term transplant outcomes in relation to a subtle pre-transplant risk assessment including solid phase antibody testing for detailed characterization of preformed DSA and a thorough evaluation of a variety of clinical and immunological variables.
Torque Teno Virus for Immunologic monitoring after kidney transplantation
The Torque Teno virus (TTV) is an apathogenic and highly prevalent virus, which is not affected by conventional virostatic therapy. Its replication is dependent on the hosts' immune status. In transplant recipients, TTV viral load is associated with organ rejection and infection. Therefore TTV might serve as a tool for holistic immunologic monitoring.
Our group has demonstrated an association between TTV viral load and the occurrence of late ABMR after kidney transplantation. Recently, we have proven TTV load to be predictive for infectious disease after kidney transplantation. Future work will focus on TTV guided immunosuppression following solid organ transplantation.
Dissecting the roles of antibodies and classical pathway of complement activation in transplant rejection
Recently, novel therapeutics targeting the complement system have been proposed for prevention or treatment of antibody-mediated rejection. In this project we want to establish an in vitro cell culture model that mimics the attack of donor-specific antibodies (DSA) and complement on endothelial cells and implements these novel agents.
There is an ongoing debate on the individual contributions of antibodies and complement to tissue damage in allograft rejection. Using our cell culture model we plan to copy this condition by incubating immortalized human blood endothelial cells with DSA and complement and analyze on a molecular level (FACS, Multiplex Immunoassays, RNA-Seq) the impact of this treatment on the cells. In parallel, we will block the complement cascade on different levels of its activation by using novel therapeutics like anti-C1s antibody TNT009, the anti-C5 antibody Eculizumab or other inhibitors of complement in order to unravel the contribution of early and late complement components or the DSA alone to particular changes of the endothelial gene expression. In a later stage we plan to extend this model by co-cultivation of purified immune cells with the endothelium.
Novel apheresis-based strategies for enhanced HLA and ABO antibody depletion
The objective of this scientific project is to establish innovative strategies for enhanced ABO and HLA antibody elimination, including the combined use of immunoadsorption with membrane filtration.
Antibody depletion by plasmapheresis or immunoadsorption is a mainstay of current desensitization protocols in HLA or ABO antibody-incompatible transplantation. Several apheresis techniques with varying qualitative and quantitative performance have been applied to cross major immunological barriers, including semiselective immunoadsorption for non-antigen-specific immunoglobulin depletion.
A current project of our group aims at developing strategies to maximize antibody depletion by non-antigen-specific adsorbers. One promising approach could be the combined use of semiselective immunoadsorption with other complementary techniques, such as membrane filtration. In a crossover trial performed in patients subjected to immunoadsorption therapy for autoimmune disease, our study group has shown high efficiency and safety in the use of semiselective immunoadsorption combined with membrane filtration for the reduction of ABO-specific IgG and IgM. Interestingly we also detected an enhanced depletion of key complement component C1q, which has subsequently proven to significantly affect the strength and functionality of complement via C3d deposition on HLA beads. This proof of concept study, which was designed as a randomized crossover trial has led us straight to the point where the strategy of combined apheresis will be tested in the setting of living-related ABO-incompatible kidney transplantation. In this dual-center pilot study (clinicaltrials.gov, NCT02120482) where we are currently recruiting patients, colleagues from the Krankenhaus der Elisabethinen Linz are acting as our collaboration partners. Ten recipients of an ABO-incompatible kidney allograft will be desensitized by semiselective immunoadsorption plus membrane filtration. The primary endpoint of this pilot study is the incidence of antibody-mediated rejection three months after transplantation.
Humoral activity at the feto-maternal interface
The role of maternal antibodies developping during pregnancy and possibly recognizing fetal tissue remains elusive and might mirror high pathophysiologic relevance.
Feto-maternal allo-recognition appears to facilitate regular placental development by controlled inflammation. This delicate balance is orchestrated by a multitude of finely regulated mechanisms of active tolerance towards the foetus including prevention of excessive antibody-mediated complement activation.
Recent data of our group suggest a pathophysiological involvement of HLA antibodies in preeclampsia. Current work focuses on the prognostic value of HLA antibody quantification and characterization in early pregnancy to provide a useful tool to increase diagnostic awareness in women prone to develop preeclampsia.