Functional testing of kidneys tissue-engineered from renogenic stem cells.

Lay summary

This project is about a new approach to the challenge of engineering complex organs for medical purposes.

One of the most pressing goals of biological engineering is to find a way to make a functioning, transplantable organ from a simple culture of stem cells. Success in this area will bring direct benefits to patients, economic relief to the NHS and taxpayer, and will provide significant opportunity for industries who take up the challenge of producing organs to order.

Existing work in the biotech industries has centred mainly on making clinical grade stem cells and setting them up to make specific tissues. The gap between cultures of stem cells, which are essentially un-arranged, and the highly intricate anatomical arrangements of complex organs such as kidney remains unbridged. Until the gap is bridged, stem cells will be of only very limited practical use for patients with serious organ failures.

We have recently developed and published a novel engineering technique for turning a simple suspension of individual foetal stem cells into a 'mini-kidney', essentially identical to a real foetal kidney except that it has no blood system. We now propose to engineer in a blood system, and to test the ability of our engineered kidneys to filter blood and excrete substances as a normal kidney would. We also propose to test how robust our method is (how well it corrects errors automatically, as we expect it to).

The direct impact of this project will be to provide an engineering technique by which kidney stem cells can be used to build real organs, potentially useful for transplants. In addition, we expect our technique to be applicable to other organs and tissues, so it may have a much broader impact in the general area of biological engineering.

This proposal addresses a priority area of MRC-MCMB: tissue engineering for regenerative medicine. It will test the physiological function of 'kidneys' tissue-engineered by a method developed in this lab: an important step in closing the gap between cultured stem cells and transplantable organs.

We have published a 2-step technique that turns suspensions of embryonic kidney stem cells into all of the epithelial and mesenchymal structures of a typical foetal kidney (Bowman's capsule, proximal and distal tubule, collecting duct, stroma etc), arranged and connected correctly, and we have pilot data showing that these engineered kidneys will become vascularized and will filter blood when transplanted into an adult host. We now wish to test, robustly and quantitatively, their functional ability:

1) We will add endothelial cells, grafted vessels in normal culture, and chick endothelia in chorioallantoic membrane (CAM) culture, to assess the ability of engineered kidneys to construct an anatomically-correct blood system.
2) We will use the fact that blood will be flowing in the CAM system (powered by the chick embryo heart) to test glomerular filtration using a standard labelled tracer method.
3) We will test active transport of organic anions and cations in the proximal tubules using labelled tracers: this will not depend on the success of parts 1 and 2 because it does not require flowing blood.
4) We will assess the robustness of the engineering system and its ability to self-correct deliberately-introduced errors of cell balance and arrangement. We have theoretical grounds to expect this.

Overall, this proposal advances our existing re-creation of basic renal anatomy to determining functional attributes. Afterwards, if the engineered organs perform as well as we expect, we can justify testing their ability to substitute for natural kidney function when matured in adult hosts. The self-organization based technology has more general biotech implications.

Impact Summary

There are 5 main classes of beneficiaries; they are listed here in order of immediacy (time) of direct impact;
1 - Academic bio-engineers (impact within time-scale of project)
2 - Biotech industry (impact probably just after project, maybe during)
3 - Public (meaningful impact several years away, but along a clear development path).
4 - Government (ditto).
5 - Third sector (ditto).

Academic research: Direct benefit to others trying to engineer complex tissues, as our technique is probably applicable far beyond the kidneys on which this project will focus. This impact on the academic community that can broaden the range of applicability of the engineering technique is a multiplier of all of the benefits below. There is also a small benefit to basic scientific understanding, which is detailed in the Case for Support section.

Biotech: The most direct benefit to biotech will be a viable engineering path from stem cells to *complex* organs (at the moment, only simple tissues can be made). This is a big multiplier of value already invested in stem cell technology, and can impact profit, growth and range of application. The type of work is ideally suited to UK SMEs. A second, small effect, comes from the training of people (who attend our proposed workshop, open to industry as well as academia) in exactly these techniques. Biotech, as well as academia, can research applying our engineering techniques to other tissues and organs.

Public: the shortage of transplantable kidneys (waiting list c. 7000 and growing) causes significant suffering (dialysis is painful, time-consuming and robs people of freedom and productivity). A technique for engineering kidneys from stem cells would provide great benefit; even more if it could be applied to other organs too. Plus, of course, indirect benefits from growth of a vibrant biotech industry.

Government: Maintaining kidney patients on dialysis is doubly expensive; directly to the NHS and also in respect to loss of time from individuals hooked up to a dialysis machine when they could be productive. Production of transplantable organs would alleviate both problems. ALSO, government research councils have ploughed a lot of money into stem cells without much to show for it in terms of a medical advance that the taxpayer can see and feel has been value. Having a bridge from stem cells to organs would be a valuable concrete example of why funding research is useful.

Third Sector: medical charities will have the same benefit as mentioned above for government research councils.