Collectin-11 as a trigger of the innate immune response in renal transplantation

When an organ is transplanted from one person to another, the disturbance of blood flow caused by the transplant procedure frequently results in inflammation. Substantial tissue damage can occur during the phase of oxygen deprivation and during the restoration of blood flow, when the kidney is exposed to harmful oxidants. The loss of healthy tissue and subsequent scarring may shorten the life of the transplant and of the patient.

Complement is a set of inflammatory molecules, which we have found is easily activated during kidney transplantation. Activated complement can contribute greatly to renal transplant injury, as our past research has shown. Our current research has identified a possible trigger for this injury; originally called kidney collectin, this trigger was later renamed collectin type-11.

Our exploratory studies have indicated that collectin-11 is released into kidneys after the flow of blood is interrupted. A series of biochemical steps initiated by collectin-11 then appears to halt the recovery of the transplanted organ. We need to work out how collectin-11 attaches to the cells of the kidney after release. We also need to find out how collectin-11 can transform the transplanted kidney into an inflamed organ by unleashing the complement system.

It is vital to work out the detailed biochemical steps, so that we can learn how to protect the donor organ from collectin-11. What we learn from this study will help medical science to develop more accurate monitoring of the transplant - which most likely will involve a simple urine test. The findings will also help us to work out how to shield the donor organ before it is transplanted. We already have methods for coating the donor organ with protective therapies. This work can tell us if more effort should be directed towards blocking collectin-11.

Given the shortage of donor organs and reliance on kidneys that have been removed after circulatory arrest, the urgency to protect these donor organs from blood-flow damage is very high. We depend on basic research to direct our efforts; here collectin-11 seems an important new target because of its proximity to the early pathway of events that trigger the inflammatory reaction. Potentially, treatment could prevent a substantial amount of damage and extend the life of the kidney transplant.

Collectin-11 (CL-11) is a collagen-containing lectin molecule that recognises carbohydrate residues on pathogen surfaces and mediates pathogen elimination. As a trigger for complement activation, CL-11 is likely to have pathological functions induced by non-infectious agents, but this remains to be shown. Given the high basal expression of CL-11 in the tubulo-intestinal compartment of the kidney, CL-11 could be a local trigger involved in renal ischaemia-reperfusion injury, which we have shown is strongly complement-dependent and a cause of accelerated transplant loss. In support, we have generated evidence in CL-11 deficient mice of protection from the effects of ischaemia-reperfusion insult. We also find that cultured renal tubular epithelial cells bind CL-11 following cellular stress. We propose that carbohydrate ligands (very likely L-fucose) on the tubule cell surface or glycocalyx coat are exposed by cell stress and cause attachment of CL-11. We anticipate that cell-bound CL-11, which is known to form a complex containing the proteolytic enzyme MASP-2, induces lectin-pathway mediated cleavage of C3, thereby releasing effector products with known inflammatory and pro-fibrotic functions. The proposed experiments using knockout-mice and biochemical analysis of CL-11 interactions on cultured renal tubule cells should solve a puzzle concerning how the destructive mechanism mediated by C3 on the renal tubule surface is initiated. Placing CL-11 on the path between oxidative stress and epithelial inflammation will create new opportunities to track and block these interactions for patient benefit.

Benefits to the scientific community:

Improved scientific methods and training skills, and understanding of scientific issues, which can deliver broader knowledge and solutions in transplantation, through:

1. Combining gene knockout technology with the skills of murine kidney transplantation providing a powerful method for discriminating the actions of locally derived CL-11

2. Drawing parallels through human biopsy and urine analysis to establish clinical relevance and develop possible biomarker applications of CL-11

3. Understanding, in terms of complement, the concept of pattern recognition receptors and damage-associated molecular patterns, and how this fundamental principle can be exploited for patient welfare

4. Showing how the principle of multivalent binding of a pattern recognition molecule to high density carbohydrate ligand can inform the design of a high avidity engineered protein for therapeutic blockade

5. Continued investment in developing highly skilled researchers to sustain research excellence that can be rapidly translated for the benefit of transplant patients, in accordance with Strategic Aim Four of the MRC Strategic Plan: 'Supporting scientists' to do world-class research

Evidence of progress should be visible within 3 years

Benefit to patients:

1. Improved quality of life and graft and patient survival rates, fewer interventions including less use of drug and dialysis treatment:

2. Faster recovery of the donor organ after transplantation, reduced stimulus for rejection and an increase the life of the donor organ and of the patient, through treatment to lower the impact of ischaemia reperfusions injury

3. Having to take fewer drugs to prevent rejection through more effective treatment of the donor organ (as opposed to extra treatment of the recipient) would reduce the frequency of lethal and non-lethal side effects associated with conventional immunosuppressive drugs

4. Shorter wait for a kidney transplant, as more donor organs would be available for transplantation through the use of treatment with potential to prevent ischaemia-reperfusion damage.

Fewer patients with failed transplants returning to the waiting list, by prevention - though early intervention - of tissue fibrosis and chronic graft failure secondary to early inflammatory injury.

Evidence should be visible within 10 years
Benefits to the NHS:

Cost/resource/efficiency benefits gained through costs of treatment (drug and dialysis costs) and patient and graft outcomes:

1. Lower dialysis costs by enabling more transplants to be carried out with the use of collectin-based therapy and by fewer patients having to return to dialysis after transplantation

2. Lower cost of dialysis in the early post-transplant period due to more rapid recovery of treated patients

3. Lower maintenance drug costs by keeping patients on fewer drugs where graft acceptance is improved by collectin-based approaches

4. Increased patient and graft survival rates with wider application of these treatment technologies, within 10 years

Benefits to the Economy:

Healthcare savings, since maintenance on a transplant is more cost-effective than dialysis. Compared with dialysis, kidney transplantation is more cost-effective over a five-year period (£45K, versus £125K for haemodialysis).

Benefits to Wider Society:

Engagement/participation, leading to:

1. Public confidence in organ donation, building on our ability to engage with the public and influence policy on matters that include research in transplantation

2. Influence willingness to participate in organ donation schemes by appreciating the scientific commitment through research

3. Building confidence in the strategic investment of public funds in transplant research

4. Involvement of the public in ethical issues that affect moving the boundaries of research to the organ donor, to allow earlier application of preventative therapies