Ann-Maria Gramkow

Monitoring of renal transplant patients by use of complement factors, kidney-specific methylated cell-free DNA, Torque Teno Virus and epitope matching

Kidney transplantation is the best treatment of end-stage kidney disease, not only regarding survival and morbidity but also regarding quality of life. In Denmark, 250-300 patients are transplanted each year, 60-100 patients at OUH.

Even though the outcome of renal transplantation has improved, we still face serious challenges. One challenge is the adjustment of the immunosuppressive treatment. After kidney transplantation, the patients receive immunosuppressive treatment in order not to reject the kidney. Unfortunately suppressing the immune system comes with serious side-effects. We treat all patients after standard immunosuppressive protocols, but patients respond differently to the same doses, which means some patients become over-immunosuppressed with increased risk of infections and cancer, while other are under-immunosuppressed leading to acute or chronic rejection. We would reduce complications and hospitalization significantly if we were able to adjust the immunosuppressive medicine much more precise. To do this, we need biomarkers of the overall immunosuppressive state of the patient.

The search for the perfect biomarker reflecting the overall immunosuppressive state has been ongoing for long and has not yet succeeded. The biomarker has to be precise, affordable and easy to use. A promising biomarker of graft injury is donor-derived cell-free DNA (ddcfDNA). DdcfDNA is released to circulation when the kidney is damaged. Unfortunately, the biomarker is not easy to analyze. We will develop a biomarker analyzing kidney-specific cell-free DNA which theoretically should perform as well as ddcfDNA, but is easier to analyze and more affordable.

The immune system is alert and activated after kidney transplantation and with episodes of rejection. A part of the innate immune system is the complement system, a cascade system which can inflict severe tissue injury and alert the immune system. Ongoing trials are testing medication able to modulate the complement system. The role of the complement system in transplantation and especially rejection needs further investigation.

After renal transplantation the suppression of the immune system causes viruses to replicate. Some viruses cause disease, but we also carry viruses which are not harmful to us and the degree of replication of these viruses might be able to reflect the state of the immune system.

Even though the outcome of transplantation is improving a transplanted kidney only lasts for an average of 15 years, which means that especially children need several transplantations during their life. Unfortunately, re-transplantation is hampered by the development of antibodies against the foreign tissue types presented to the immune system. More awareness is arising to the meaning of matching not only tissue type but also considering the structural appearance of the tissue type. This approach to matching donor and recipient could diminish the development of antibodies and help us predict in which patients’ reduction of immunosuppression are safe.

Aim of the study

To develop, validate and explore 3 potential biomarkers of under- and over-immunosuppression. To investigate how matching a Danish pediatric kidney transplant cohort on epitopes affects renal outcome and development of antibodies against HLA haplotypes.

Strength and feasibility

We address a clinical and relevant problem affecting all renal transplant patients. We have already prospectively collected the blood and urine samples needed to complete the study. We have a project group with the skills and knowledge to complete these studies successfully.

Hypotheses and method

We will perform 5 sub-studies which all use blood and urine samples from the biobank, BioTX, consecutive gathered from consenting transplant patients from 2016 and onward. All transplant patients are asked for consent and the biobank meets great support from the patients, over 250 patients are now included. The urine and blood samples for this project are ready to use.

Study 1

Complement split-products as a biomarker of rejection. Hypothesis: Complement split-products increase in patients with rejection.

Study 2 and 3

Development and validation of methylated kidney-specific cell-free DNA as a biomarker of rejection and graft injury. Hypothesis: Methylated kidney-specific cell-free DNA will increase in patients with rejection and graft injury.

Study 4

Torque Teno Virus (TTV) as a biomarker of over-immunosuppression. Hypothesis: TTV will increase in infected patients.

Study 5

Epitope (structural) mismatch in a group of renal transplanted children. Hypothesis: The structural mismatch can predict the development of antibodies against the foreign tissue type of the kidney.