Ultrasound for rapid and uniform rewarming of large volumes of cells and tissues after cryopreservation

Over 120,000 people in the USA and over 6000 people in the UK are waiting for organ transplants, and many more are suffering from organ failure. Many donor organs are not transplanted (approximately 60% of donor hearts and 20% of kidneys are not used), often because they can only be kept for a short time. Long term preservation would mean better matching with recipients over larger geographical areas, reducing the chances of rejection and increasing the number of organs that could be used. One potentially transformative method of preserving organs for a longer time is cryopreservation. This involves freezing the organs at very low temperatures and then defrosting them when needed.

However, this is currently limited to small volumes (<3 ml), largely due to the difficulty in rewarming the tissues without damage after freezing. To avoid damage on rewarming, tissues must be heated quickly and uniformly. This is not possible with existing water bath methods so the development of new methods for volumetric rewarming of large tissue volumes is critical.

The aim of this fellowship is to develop a novel method of tissue rewarming using ultrasound. As ultrasound passes through frozen tissue, it loses energy which is deposited as heat. By controlling the pattern of the ultrasound waves entering the tissue, heat can be deposited as needed to raise the temperature of the tissue quickly and uniformly. First, the ultrasound parameters will be optimised for maximum cell viability and optimal heating rate using small volumes of cells. An ultrasound array based on these parameters will then be developed with methods of steering and shaping the acoustic field to uniformly and rapidly heat larger volumes of cells. This will be extended to warming tissues with inhomogeneous acoustic and thermal properties and larger volumes, using real time feedback to control the heating distribution, with the ultimate vision of creating a fully flexible tool that can be used to rewarm whole organs. Ultrasonic volumetric warming has the potential to enable long-term storage of tissues and organs which would transform the availability of organs for transplant. It would also have many other applications such as increasing access to therapies involving implanting cells and tissues in the body for diseases such as type 1 diabetes or for restoration of fertility after cancer therapy.

In the long term, ultrasonic rewarming will enable the successful cryopreservation of large volumes of cells, tissues and whole organs. This will help to enable organ banks for on-demand supply of donor organs, bioartificial organs, tissues and cell therapy products. This capacity will lead to improvement in treatment for people suffering from a vast number of conditions, significantly reducing morbidity and mortality, adding quality-adjusted life years for patients, as well as reducing costs of ongoing care and patient support. In general, the main beneficiaries in this context include: (1) people suffering from organ failure, who could be treated by organ transplant; (2) sufferers of diseases which result in compromised organ function, usually treated by means other than transplants, e.g. type 1 diabetes; (3) child and young adult cancer survivors in whom fertility may be restored by preservation and autotransplantation of reproductive tissues. Additionally, the wider public and patient population will benefit from the increased effectiveness of the health service due to cost savings and availability of more advanced therapies.

Preservation and re-implantation of ovarian tissue for restoration of fertility in child and young adult cancer survivors is now offered as a clinical service at a number of hospitals worldwide. Around 100 live births have been reported so far as a result, with huge impact on the quality of life of these patients, but the chance of success is currently around 50%. Increased success could be achieved by improving tissue viability. This could be achieved with more consistent and optimised rewarming of the tissues. Clinical translation of ultrasonic rewarming will be pursued to deliver this impact in the shorter term. In the longer term, the technique could also be extended to the re-implantation of whole ovaries and testes.

Almost 10% of patients of the transplant list are waiting for a liver. With increases in liver disease resulting in increased demand for (usually urgent) transplants, the use of a bioartificial liver is an important alternative. Widespread clinical use would require on-demand access to large volumes of cells, which would be enabled by the development and clinical translation of ultrasonic rewarming in the medium term.

In the long term, increased rates of organ transplant and access to cell therapies, enabled by storage and preservation of cells and donor organs, would provide significant savings in NHS spending. For example, almost 80% of the 6000 people currently on the UK transplant list are waiting for kidney transplants, with a mean waiting time of over 2 years, and a further 30,000 people in the UK are currently on dialysis. The cost of medication and aftercare following a kidney transplant is approximately 15% of the cost of renal dialysis (which costs the NHS over £0.5bn pa), and allows patients to return to a quality of life similar to that which they experienced before becoming ill. In terms of cell therapies, one example is islet cell transplant to restore insulin production, which can cure type 1 diabetes, reducing morbidity and dramatically reducing the cost of ongoing care and support (~£2bn pa) of these patients.

There are a huge number of potential applications of cryopreservation of cells, tissues and organs. To fit with a future vision of organ banks and centralised infrastructure for cell therapy manufacturing and distribution, rewarming equipment will need to be widespread for local access. The developed devices will be commercially attractive. Commercial translation will be pursued and it is expected the generated IP will lead to licensing agreements or the development of new start-ups, with the UK becoming a base for future international investment. This would expand the cryochain industry, generating new jobs and revenue. The devices will also be of commercial value as a research platform for cryopreservation and cryobiology research.