Exosomes and machine perfusion as a therapy to improve organ transplantation

Cellular therapies are cutting-edge technologies that are now expanding into all spheres of medicine including transplantation. We are increasingly reliant upon marginal or less optimal donor organs for transplantation, however, to close the ever-widening gap between organ demand and supply. Such organs have higher discard rates and less ideal short and longer-term outcomes and ideally require improved organ preservation and resuscitation methods which can be utilised regardless of the jurisdiction.¹ Various cellular therapies are gaining significant momentum as a novel approach to reducing transplant organ ischemia/reperfusion injury (IRI), and potential improvement in graft outcomes. As seen in Figure 1, machine perfusion of organs provides the ideal setting to specifically deliver many targeted therapies to individual grafts, including therapies such as; stem cells, organoids, viral transduction, nanoparticles, and the use of exosome-based treatments.²

Exosomes are small extracellular vesicles (30–150 nm in diameter), that play a unique role in cellular communication, derived from the endosomal pathway, with intraluminal vesicles being formed in multivesicular bodies and subsequently released with fusion of the plasma membrane. Unlike traditional cell-based therapies, exosomes do not contain live cells, reducing concerns about immune interaction in both the organ and subsequently recipient. In the study by Burdeyron et al.³ innovatively delivered exosomes derived from porcine urine progenitor cells (UPCs) to kidneys using hypothermic and normothermic machine perfusion (HMP and NMP).

IRI is a critical challenge in transplantation, particularly impacting organs from extended criteria donors and those from donors after circulatory death. These types of organs are generally more sensitive to ischemia, with attendant magnification of injury during reperfusion, and a subsequent higher incidence of graft dysfunction/rejection.⁴ Technologies such as HMP and NMP are variably employed by different centres to improve organ quality prior to transplantation. HMP involves the continuous circulation of a cold preservation solution through the kidney, whilst NMP involves perfusing the kidney with a warm, oxygenated solution to simulate physiological conditions. While these methods offer some protective effects, they do not completely ameliorate IRI, and significant further work is required to enhance their efficacy.⁵

Exosomes carry bioactive molecules, including microRNAs (miRNAs), mRNAs, and proteins, which can influence cellular interaction and regulate immune activity. Exosome-based therapy can leverage the potential for intercellular communication, signalling cascades, and other physiological effects without the complexity and risks associated with administering whole cells. Studies have shown that exosomes derived from various cell types, including mesenchymal stem cells (MSCs) and UPCs, possess anti-inflammatory, anti-apoptotic, and pro-angiogenic properties, making them promising agents for mitigating IRI. This can include certain miRNAs that can reduce the expression of pro-inflammatory cytokines such as interleukin-6 and tumour necrosis factor-alpha, which are major contributors to IRI and organ damage.⁶

MSCs are commonly used in regenerative medicine, and their exosomes have shown promise in protecting organs from IRI in both preclinical and clinical studies. For example, MSC-derived exosomes were demonstrated to protect rat kidneys and livers in different IRI models/studies, with preservation of cell viability and modulation of inflammatory responses.⁷

UPCs offer a unique advantage as a source of exosomes because they can be non-invasively collected from urine, unlike MSCs retain anti-inflammatory/regenerative capabilities, and their renal origin potentially makes them more compatible with renal-targeted transplant therapies.

In the study from, Burdeyron et al.³ porcine UPC-derived exosomes were isolated and characterised, then used in their ex vivo kidney model. By using HMP and NMP to deliver the exosomes, researchers observed significant improvements in kidney tissue integrity, reduced inflammation, and lowered levels of cell damage markers. This effect is likely due to the bioactive molecules within the exosomes that modulate immune and inflammatory responses at the cellular level, ultimately reducing damage and promoting tissue repair.

The ability of NMP to mimic physiological conditions means that it can support exosome uptake and interaction with tissues in a way that the current static cold storage methods cannot.⁸ Rigo and colleagues demonstrated that human liver stem cell-derived extracellular vesicles (HLSC-EVs) treatment for 4 h effectively reduced liver injury during hypoxic NMP.⁹

While exosome-based therapies present an exciting avenue for reducing IRI and improving transplant outcomes, there are still several challenges to address. The standardisation of exosome isolation, composition, and characterisation is crucial for ensuring consistent therapeutic quality, safety, and efficacy for use in transplantation.

There is also a need for a deeper understanding of the specific bioactive molecules within exosomes responsible for their protective effects. Identifying the most effective exosome-derived miRNAs, proteins, and other molecules could lead to targeted exosome modifications that enhance their therapeutic potential. For instance, exosomes could be engineered to carry higher levels of specific anti-inflammatory or regenerative miRNAs, tailoring them to the needs of specific transplant applications.

Moreover, clinical translation will require comprehensive testing to confirm the safety and efficacy of exosome therapy in large animal models prior to application in patients. Human studies will also be required to verify that these therapies can deliver consistent results without unintended side effects.¹⁰

As detailed by Burdeyron et al.³ exosomes derived from urine progenitor cells, administered via HMP and NMP, can enhance the mitigation of ischemia/reperfusion injury in a porcine kidney model. The potential of exosome therapy extends beyond kidneys, as studies in other organs have also demonstrated. By leveraging the protective and regenerative capabilities of exosomes, researchers can improve outcomes for grafts from marginal donors and address the current overwhelming organ shortage for transplantation.

Exosome-based therapies represent an innovative approach in transplantation medicine, offering a potentially safer and more controlled alternative to whole-cell therapies. This approach harnesses the therapeutic benefits of stem cell signalling without introducing live cells, potentially reducing risks associated with immune rejection. Future research into exosome isolation, characterisation, and engineering will be crucial in making this therapy a practical, safe and efficacious solution in the clinical setting.

Wayne Hawthorne devised, wrote and revised the manuscript and figure. Rajith Amaratunga revised the figure. Ahmer Hameed revised the manuscript.

The authors declare no conflict of interest.