Renal immunology and transplantation

Moreover, there is a strong focus on developing and implementing novel immunosuppressive therapies, including cell therapy and immunotherapy. These goals are implemented by epidemiological, clinical, histochemical, biochemical and experimental approaches. This research program of fundamental immunology and nephrology is highly integrated with the clinical program of the department and is currently focused around the following specific themes:

Glomerulonephritis: Immune monitoring is an important part of the research unravelling the amplifying mechanisms of auto-antibody mediated diseases like systemic lupus erythematosus (SLE) and ANCA-associated vasculitis (AAV). We have developed methods to quantify neutrophil extracellular traps (NETs) to monitor this potential autoantigenic load in patients with SLE and AAV, and make use of high-sensitivity flowcytometry technique to monitor immunological effects of novel strategies of immunotherapy in SLE and AAV patients. This is organized in the context of the Leiden outpatient clinic for Lupus, Vasculitis and Complement-mediated Systemic diseases (LuVaCs) which accommodates top-referral, multidisciplinary, tertiary care on a regional and national level.

Within LuVaCs, research activities are divided in two main areas: ‘novel treatment strategies’ and ‘innovative immunomonitoring’. Both areas are closely related because the search for novel treatment options in SLE and AAV almost simultaneously requires the need for new immunomonitoring tools. Immunomonitoring in SLE and AAV patients helps to better understand a) the underpinning immunological pathophysiology and b) the beneficial effects of novel treatments on autoimmunity. In addition, immunomonitoring can potentially help doctors and patients when choosing a personalized treatment strategy, to define response to treatment on a clinical as well as an immunological level and to predict prognosis of the disease. Several Investigator Initiated clinical studies are ongoing in the area of SLE and AAV.

Kidney transplantation is the preferred option for patients with end stage renal disease, but requires lifelong immunosuppression. For balanced use of immunosuppressive agents, it is of critical importance to have biomarkers which allow a close monitoring of the allo-specific immunity as well as of the ongoing inflammatory and injury response. Upon organ transplantation, ischemia/reperfusion is an early and inevitable process, and the innate immune system has been implicated as a critical mediator of injury. Recent developments include the use and optimization of machine perfusion, to allow improvement of ‘suboptimal’ donor organs and to monitor the immunogenicity. This expertise is shared with the research in the area of Regenerative Medicine, where clinical application of cells and tissues will be confronted with similar immunological hurdles. We have already clinically applied cell therapy with Mesenchymal Stromal Cells (MSC) to allow safe withdrawal from calcineurin inhibitors. This is all organized in the context of the LUMC Transplant Center (TRAX).

Complement activation has been recognized as an important effector arm of the immune system, not only as a defense against pathogens, but also as a pathogenic mechanism for antibody-mediated processes (humoral rejection, SLE) or as a clearance mechanism for the removal of cellular debris. Interest in complement has strongly increased with the availability of therapeutic agents which can be applied in the clinical setting. This requires an in depth view of the pathways involved in the complement activation, especially to discriminate between systemic effects and local (tissue-related) mechanisms of activation and regulation. This is exemplified by the tight regulation at the vascular interface, and the occurrence of ‘thromboinflammation’ in conditions where regulation is disturbed. In our current projects we are investigating especially the regulators of the alternative pathway, the amplification loop of the system, and develop the tools to monitor complement activation in experimental models. This is a pivotal prerequisite for the introduction and use of novel therapeutic complement-inhibitors which have entered the clinical arena.

We have established methods to generate and characterize tolerogenic antigen presenting cells (dendritic cells and macrophages) in human and rat and applied these in experimental renal transplantation models. In vitro experiments with human monocyte-derived DC concentrate on the immune regulatory mechanisms of corticosteroids and have established a differential regulation of cytokines from the IL-12 family. Understanding of the fundamental mechanisms and local factors that influence skewing of myeloid precursor cells are key to the design and discovery of new strategies in preservation of organ transplants and dampening of ongoing immune and inflammatory responses.

For balanced use of immunosuppressive agents, it is of critical importance to have biomarkers which allow a close monitoring of the allo-specific immunity as well as of the ongoing inflammatory and injury response. We have an ongoing project (together with the department of Immunohematology) to evaluate and monitor the indirect pathway of allo-recognition.

Clinical studies with mesenchymal stromal cells (MSC), as a strategy to safely taper immunosuppressive therapy, are ongoing within the department. These trials, making use both of autologous and allogenic MSC, are conducted in patients receiving a kidney of a living donor. We apply advanced strategies of frequent immune-monitoring to determine safety, efficacy and mechanism of action of this form of cell therapy.

Ischemia/reperfusion is an early and inevitable process organ transplantation, and the innate immune system has been implicated as a critical mediator of injury. In a combination of clinical, experimental and in vitro experiments we have established a new role for Mannan Binding Lectin (MBL), the initiator of the lectin pathway of complement. Recipients with low MBL show improved graft survival, whereas therapeutic inhibition of MBL in a rat model of IRI results in a complete protection against injury. Currently we are investigating the molecular mechanism of MBL-mediated injury, which appears to be independent of the complement activation.

Complement activation has been recognized as an important effector arm of the immune system, not only as a defense against pathogens, but also as a pathogenic mechanism for antibody-mediated processes (humoral rejection, IgA-nephropathy, SLE) or as a clearance mechanism for the removal of cellular debris. Interest in complement has strongly increased with the availability of therapeutic agents which can be applied in the clinical setting. This requires an in depth view of the pathways involved in the complement activation. In our current projects we are investigating especially the contribution of properdin, a stabilizer of the alternative pathway, and develop the tools to monitor complement activation in experimental models.

The central role of complement in disease pathogenesis is best illustrated by renal diseases collectively termed ‘complement-mediated renal diseases’ which include atypical HUS and C3-glomerulopathy. The LUMC is recognize as an expertise center for these diseases, and this is supported by research performed in the context of the COMBAT consortium. This consortium, coordinated from Leiden, aims to couple basic knowledge on complement to the development of assays essential for accurate diagnosis and disease monitoring. This is a pivotal prerequisite for the introduction of novel therapeutic complement-inhibitors which are approaching the clinical arena.

In view of the importance of local immune and inflammatory processes, we have developed immunohistochemical methods to characterize and quantify myeloid subsets in human renal biopsies (pre-transplant, protocol- and rejection biopsies). We have been able to demonstrate that the composition of infiltrate has an impact on the long term function of transplanted organs. Moreover we found that during rejection, also plasmacytoid DC were a major component of the infiltrate. Plasmacytoid DC are the natural alpha-IFN producing cells and implicated in defense against viral infections. Since viral (re)-activation (CMV, BK) is a major complication in immunosuppressed individuals, we investigate the contribution of pDC in this process.

For balanced use of immunosuppressive agents, it is of critical importance to have biomarkers which allow a close monitoring of the allo-specific immunity as well as of the ongoing inflammatory and injury response. We have an ongoing project (together with the department of Immunohematology) to evaluate and monitor the indirect pathway of allo recognition. Moreover we are exploiting the urine as a source of biomarkers, both using a hypothesis driven strategy (KIM-1, NGAL, MBL) as well as using an unbiased strategy of metabolomics (in collaboration with the departments of CPM- Center for Proteomics and Metabolomics and department of Clinical Chemistry)

Immune monitoring is also an important part of the research unravelling the amplifying mechanisms of auto-antibody mediated diseases like systemic lupus erythematosus (SLE) and ANCA-associated vasculitis (AAV). We have developed methods to quantify neutrophil extracellular traps to monitor this potential autoantigenic load in patients with SLE and AAV, and make use of high-sensitivity flowcytometry technique to monitor immunological effects of novel strategies of immunotherapy in SLE and AAV patients.