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Reinventing Liver Paired Exchange


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The Story of a Revolution in Liver Transplantation | Sarkac.org

Authors: Defne Üçer Şaylan, Tayfun Sönmez, and Utku Ünver in Sarkaç, the popular science platform of Science Academy Turkey August 31, 2023

https://sarkac.org/2023/08/karaciger-nakillerinde-bir-devrimin-hikayesi/

Translated from Turkish (with the help of ChatGPT 3.5 https://chat.openai.com/)

 

 

In July 2022, a 4-way liver paired exchange was performed for the first time in the world. Four individuals in need of liver transplants but without compatible donors were able to obtain compatible organs by exchanging their donors. This event took place at the Inonu University Liver Transplantation Institute in Malatya, thanks to the liver-paired exchange system developed by the economist members of the Science Academy, Tayfun Sönmez and Utku Ünver.

 

You might wonder what economists have to do with liver transplantation; in the interview, you will read below, Sönmez and Ünver explain the scientific adventure that led to the establishment of this system.

 

Economics studies “how limited resources can be allocated most efficiently in its most general sense.”[1] The resources mentioned here can be monetary, but they can also be many other things, such as vaccines produced during a pandemic, university dorm rooms, housing units, donated organs, or available slots in university departments. In these allocations, having money doesn't necessarily give you an advantage; in other words, even if you have the money, you can't necessarily get the apartment you want or the kidney that will save your life. This is what is known as "matching markets."[2]

 

Lloyd Shapley, who laid the theoretical foundation for matching markets, and Sönmez and Ünver’s colleague Alvin Roth were awarded the Nobel Prize in Economics in 2012. This award covered not only the analysis of resource allocation in theory but also the redesign of real-world institutions.[3] The "Banu Bedestenci Sönmez Liver Paired Exchange System" established in Malatya is an example of such an economic institutional design.

 

Listening to Sönmez and Ünver, I thought that what they were describing is a remarkable example of the "interdisciplinary" approach that prioritizes combining scientific rigor and competence with societal issues, which I have frequently heard about in recent times.[4] When working on a system that will save more lives, is it more valuable to create the most efficient system mathematically or to focus on a system that can be practically implemented in the real world, one that can convince decision-makers? The scientific value of the former is undoubtedly undeniable, but can the second approach be the only condition for improving the world?

 

Sönmez and Ünver's work, which prioritizes bringing real solutions to societal problems, has evolved into a comprehensive methodology over the years. In the next issue, we will delve into this methodology, which Sönmez calls "minimalist market design."

 

NOTE: Since our August 8, 2023 interview, a second 4-way exchange has been carried out in the "Banu Bedestenci Sönmez Liver Paired Exchange System." As of August 29, 29 patients have received liver transplants through the program; six 2-way, three 3-way, and two 4-way exchanges have been performed.

 

Defne Üçer-Şaylan

 

 

 

Parentheses: What is an organ-paired exchange?

 

Organ exchange means that instead of every patient finding a compatible organ donor, a group of patients and donors are matched in the best possible way, even if some donors are incompatible with their recipients. This ensures that every patient gets a compatible donor, and as a result, many more lives can be saved.

 

The simplest example of organ-paired exchange is a 2-way exchange, where two incompatible patient-donor pairs can be matched, as shown in the picture. An exchange can involve a larger number of donor-patient pairs.

 

To prevent any negative consequences in case someone decides to withdraw from an organ-paired exchange, all surgeries must be performed simultaneously. In the case of a 2-way exchange, this means four simultaneous surgeries; in a 4-way exchange, it means eight simultaneous surgeries. Therefore, the capacity of transplant centers is very important.

 

 

 

Can you briefly describe the situation regarding kidney and liver transplants worldwide?

 

Utku Ünver: In many countries, organ transplantation relies on donations from deceased individuals. Depending on the country's laws, organ donations can occur either voluntarily by individuals or without consent, with available kidneys and livers from deceased individuals being transplanted to those in need. Especially in Western countries where organ donation is widespread, deceased donor transplantation is more common. On the other hand, live donor transplantation is common in countries with low organ donation rates, such as Japan, Korea, Turkey, Saudi Arabia, India, and Israel.

 

In a live donor kidney transplant, a donor donates one of their two kidneys. In a live donor liver transplant, as a person has only one liver, a portion (lobe) of the liver is donated, which is a more complex and riskier procedure compared to kidney donation. Particularly, there are greater risks associated with donating the right lobe of the liver, which is larger.

 

Live donor liver transplantation was developed and practiced in the United States; however, after two live donors who had donated their right lobes in 1999 and 2002 passed away, these incidents significantly hindered live donor liver transplantation in Western countries. In fact, this also led to a decline in number of live donor kidney transplants in the United States.

 

As a result, live donor transplantation has become more widespread in East Asian countries rather than in Western countries, and some transplant centers in these regions have advanced significantly in live donor transplant operations. Currently, the Asan Medical Center in Seoul is the world's largest center, followed by the Liver Transplantation Institute at Inonu University in Malatya. This institute has become a world-renowned center thanks to Prof. Dr. Sezai Yılmaz's incredible dedication, scientific knowledge, and the young experts he has brought to his team. The institute can perform 12 surgeries simultaneously with 6 live donors.

 

The story began in the late 1990s with the "dormitory/house allocation problem" you were working on; what was this problem, and how did it connect to organ transplantation systems?

 

Tayfun Sönmez: When I was an assistant professor at the University of Michigan at the beginning of my career, I worked on a system that ensured the optimal allocation of dormitory rooms for students, together with Atila Abdulkadiroğlu, who was pursuing his Ph.D. at the University of Rochester at the time. The problem was as follows: There are a number of dormitory rooms, some occupied by returning students, while others are vacant. Both returning and new students submit their room preferences, and an allocation is made. Students already in the dormitory have the right to keep their rooms for the upcoming semester. Everyone has a chance at vacant rooms, and the current occupants have priority in occupied rooms. In this problem, we found an algorithm that provided the best matching, and the results of this study were published in 1999.[5]

 

When Utku first came to Koç University, we worked intensively on this model. As soon as Utku arrived, I explained this problem to him, and we co-authored a paper on this model.[6]

 

Utku Ünver: In 2002, while I was working as an assistant professor at Koç University, I went to Harvard University to work with Alvin Roth, who was my Ph.D. co-advisor, with my school's permission and his invitation.  On the first day, Roth told me that Tayfun and Atila's dormitory room assignment model has a very interesting application: the kidney exchange problem.

 

Tayfun Sönmez: The connection between our model and the kidney exchange problem is as follows: Imagine the students with existing rooms as recipients and the rooms they want to change as donors. Like a student might want to change their room, the donor might not be a compatible match for a patient, or they might not be ideal. Just as in the dormitory problem, if we can provide a better room to a student, they will give up their current room. In the same way, if we can provide a compatible donor to a patient, we can match their donor with another patient. The vacant rooms in the dormitory allocation model correspond to deceased organ donations. New students without rooms can be compared to patients without live donors, who are waiting on the deceased donor list (vacant rooms). So, mathematically, the dormitory allocation model is quite similar to the kidney exchange problem.

 

Utku Ünver: While talking to Roth, I suggested that we should work on the kidney exchange model in more detail and write a paper, but Roth said, "This problem has already been solved in Atila and Tayfun's paper; there's nothing to write about here." During my stay in Boston, I gave a lecture on exchange models like the dormitory allocation model in Roth's class, using the kidney exchange system as an example. This clarified the problem a bit more, and at this stage, I mentioned the problem to Tayfun.

 

Tayfun Sönmez: I was thrilled and very excited when I heard about it. Economists had never dealt with such a problem in the literature. From that day on, we started to study the issue in detail. In the Spring of 2003, Utku and I studied everything related to kidney transplantation; we read dozens of articles and theses and learned everything from tissue compatibility to risks.

 

At that time, was the kidney exchange system being implemented worldwide?

 

Tayfun Sönmez: In 1986, Dr. F. T. Rapaport introduced the concept of a 2-way kidney exchange.[7] What does that mean? If I have a donor who is incompatible with me, and you have a donor who is incompatible with you, we exchange donors.

 

Utku Ünver: Rapaport said, "We are not keeping records of incompatible donors, but we need this data; let's create a database that includes incompatible donors," but this suggestion was not taken seriously. As I mentioned earlier, Koreans were pioneers in this regard, starting kidney exchanges in the 1990s. However, they were finding matches entirely manually, and of course, the numbers were very low.

 

Tayfun Sönmez: In 2000, kidney shortages became a significant issue, especially in the United States. Without a database, finding matches was very challenging, and patients in dialysis units were trying to find patient-donor pairs themselves. In 2000, the first 2-way kidney exchange took place in the United States. For years, only about 2-3 exchanges per year could be conducted throughout the country.

 

 

Parentheses: What does a compatible kidney mean?

 

For a kidney transplant to be feasible, the patient and the donor must be both blood type compatible and tissue compatible. There are four different blood types, and compatibility in blood types means the following. A donor can donate to a patient with the same blood type. As shown in the picture, a type-O donor can donate to all blood groups but only receive from type-O donors. A type-AB patient can receive from anyone, while a type-AB donor can only donate to their own blood type.

 

Approximately 20% of patients can also be affected by tissue incompatibility.

 

 

In the late 1990s, a second exchange method that was much easier to organize was proposed:[8] list exchange.

 

In this method, if a patient has an incompatible donor, they give the donor organ to the deceased donor list, and the patient moves up on the list. So, the exchange takes place not between two pairs but between a pair and the deceased donor list.

 

In fact, there are two mathematical structures that lead to exchanges: cycles and chains. The exchange of two pairs corresponds to the simplest form of a cycle, and the exchange shown in the figure corresponds to the simplest form of a chain. These structures can be expanded, of course, to create richer exchanges involving many more people. These structures were all developed in the paper we wrote with Atila on dormitory allocation.

 

While proposing list exchange, Ross and Woodle pointed out an ethical concern, although its organization is simpler:

 

List exchange is a system that allows someone on the deceased waiting list to give a type-A or type-B kidney to the deceased donor list and receive a type-O kidney from the deceased donor list. So, you can get a compatible and more "valuable" organ from the deceased donor list and give back an organ compatible with fewer people. In addition, the O blood group is very common among African Americans, and these individuals can only receive organs from type-O donors. So, you are affecting the distribution of the deceased donor list. They also wrote in their paper that the list exchange would harm type-O patients.[9]

 

In 2000, a consensus statement was published by doctors. It states that paired exchange is ethically appropriate and recommended but raises ethical concerns about list exchange.[10]

 

In 2001, a kidney exchange system was established in New England. Due to ethical concerns, they aimed to perform paired exchanges as much as possible rather than list exchanges, but of course, this requires organization and is not an easy task. They did not have the know-how of optimization, databases, and such, so they created a program that manually generated exchanges. Since hospitals participating in the system did not even have a common database, they had difficulty finding paired exchanges. In the following 3-4 years, they only had four 2-way exchanges, although they conducted around 20 list exchanges, about which they had ethical concerns.

 

In 2004, they published an article explaining the system's purpose and results and emphasized the value of paired exchanges.[11] In the article, they explained how they tried to overcome ethical concerns. They mentioned that when the possibility of a list exchange arose, they searched whether there was a chance for a paired exchange for the next month and attempted to do this via a telephone network. However, after being convinced that a paired exchange was not possible, they implemented the list exchange. Therefore, they conducted relatively fewer and delayed list exchanges.

 

What contribution did learning all these details about kidney exchanges make?

 

Utku Ünver: Economics has a very effective analytical method for social problems. There are many tools we use comfortably, and we can model any social problem using these tools. However, sometimes researchers can get lost in their models and lose touch with real life. They can become somewhat detached from reality, a bit like living in an ivory tower; they solve a problem, but the models they develop may not be usable in real life. If we want to solve a real problem, we must know and consider its details.

 

Tayfun Sönmez: After thoroughly understanding the details and challenges in real-world applications, we told Roth, "We have studied this; we have learned almost all the necessary details, nearly as much as doctors. The problem here is not completely solved. Also, using our algorithm for dormitory allocation as we did before may not be appropriate. Moreover, the only issue here is not just efficient matching; there are ethical concerns. We can find a solution that both solves their ethical concerns and increases the number of transplants, possibly by a factor of ten or even a hundred." At this stage, Roth was not entirely convinced yet and hinted, "The maximum number of authors for this paper is two; you two should write it."

 

So, we told him that we had learned about the problem from him, and after preparing the first draft, we would send it to him, and he could join us as an author whenever he wanted. We did the modeling, analysis, and simulations and wrote the paper. When Roth read the draft, he said, "Okay, I will join too." The order of authors in papers is alphabetical in economics, so he became the first author.[12]

 

Utku Ünver: After that, Roth sent the paper to Francis Delmonico, a transplant surgeon and the head of the New England exchange program. Noting the historical significance of economists contributing to this field, Delmonico apparently joked that “[him] talking to an economist is like Nixon talking to communist China.”

 

Tayfun Sönmez: When proposing a better solution to an established system, it is important to approach it by saying, "I have something valuable for you." In our suggested system, we were not only solving their ethical concerns but also foreseeing that we could increase the numbers by tens or even hundreds of times. When Delmonico learned about this, he got very excited, but he asked us to change our model and proposed system in three ways:

 

  1. Do not allow list exchange – If we can increase the numbers this much, let us exclude the method with ethical concerns.
  2. In our system, we were utilizing not only 2-way exchanges but also multi-way exchanges. All surgeries must be performed simultaneously, so let's allow only 2-way exchanges.
  3. Let there be only one condition: donor-patient compatibility; do not allow patients to choose. Our proposed system involved preferences, just like in the dormitory allocation problem. Delmonico suggested that we do not allow patients to choose, and the only required condition should be blood type and tissue compatibility. If we allowed stating preferences, people might not like the organs; they might have preferences over donors being young or belonging to a certain race, etc.

 

In this case, we had to change our model that solves a more layered problem completely. The seemingly simpler new problem was technically much more challenging. But if you want to find a solution to a real problem, it is crucial to identify the need well and create a special theory based on that need. Of course, for this to succeed, it is essential to go beyond what you know and learn new things. Since we had always approached a problem in our previous research with this perspective, we got to work again, and we found the right path by using an approach from the optimization literature that was similar to ours from some angles. With this approach, we created a model that met Delmonico's criteria within a few months.[13] Delmonico welcomed the new model, and in the Fall of 2004, we, along with him, established the New England Program for Kidney Exchange (NEPKE). This system became the first exchange system in the world to benefit from economic design and optimization principles.[14]

 

Initially, we started with 2-way exchanges as requested by Delmonico. It took time to establish the legal infrastructure of the program, among other things. During that time, we started receiving data, and we began analyzing the data with excitement.

 

In the meantime, mostly due to curiosity,  we also started investigating the importance of 3-way exchanges. When considering 3-way exchanges, we achieved a number beyond what we had predicted. This surprised us as well. There was a beautiful mathematical structure under this new scenario, and, even if thousands of patients were involved, the importance of 3-way exchanges was not diminishing. 3-way exchanges often increased the number by an average of 25-30%.[15] Upon this discovery, we began advocating for 3-way exchanges, which were eventually implemented.

 

Utku Ünver and Tayfun Sönmez (used with permission of Boston College)

 

 

During this time, the concept of altruistic donors, who donate a kidney without expecting anything in return, emerged. These individuals want to donate one of their kidneys unconditionally to a stranger. In the United States, at that time, only about 10-15 people per year were donating their kidneys in this way. It is essentially a form of donation similar to organs coming from the deceased donor list, but there are no ethical concerns here. The advantage here is that you don't have to perform all surgeries simultaneously, as in a paired exchange. In a paired exchange, if someone backs out, one pair has received an organ without giving one, and another pair has donated an organ without receiving one. The second pair suffers a significant loss in this scenario, so you must perform all surgeries simultaneously. In contrast, a chain starts with an altruistic donor who donates to one pair, then they donate to another pair, and even if someone drops out, the chain just remains short, so simultaneous surgeries are not required. This idea gained a lot of popularity.[16]

 

Utku Ünver: In the article we wrote in 2006, we addressed the concept of starting chains with altruistic donors and suggested that such a chain didn't necessarily have to begin with an altruistic donor; chains could also begin with deceased donors. Our suggestion has been implemented in Italy since 2018.[17]

 

While our partnership with New England continued, we began to support a system established in Ohio in 2005. This system started within Ohio but eventually became nationwide in the United States, including many transplant centers.[18] Dr. Mike Rees was the head of this system. Unlike Delmonico, who was very conservative and moved forward with extra caution, Rees wanted to make this system bigger swiftly. The Ohio-centered system started to implement our proposal regarding altruistic donor chains.[19][20]

 

Tayfun Sönmez: Altruistic donor chains quickly became the most commonly used exchange method in the United States due to their logistical convenience. Moreover, these chains significantly increased the number of altruistic donors. The fact that one donor could save many lives increased the appeal of altruistic donation.[21] Today, the two largest centers that use this system are the National Kidney Registry and the Alliance for Paired Kidney Donation, which started in Ohio.

 

How did you carry out all these works with a team?

 

Tayfun Sönmez: Throughout this process, Utku and I were mainly involved in the modeling and analytical aspects of the work, while Roth focused more on communication and outreach. We collectively determined communication strategies based on our analytical results. Roth's prominent status at Harvard University certainly played a significant role in implementing these initiatives.

 

We had a productive partnership with Roth in the initial few years, and together, we accomplished a lot for the benefit of humanity. This partnership resulted in thousands of patients receiving transplants over the past two decades. However, starting in 2006 and 2007, we noticed that, despite our leading roles in developing models, new exchange methods, analyses, and persuading doctors to adopt these methods, Utku and I were not receiving the credit we deserved. This unfortunate situation was compounded by the fact that, in economics, authors are traditionally listed in articles in alphabetical order. In my view, the way Roth presented our contributions to the public also played a significant role in this misconception. Consequently, many people started to refer to our model as “Roth’s Model.” During this period, my wife was diagnosed with cancer, making it an especially challenging period for me. As a result, I withdrew from all partnerships, including some that I had initiated myself. Utku did not leave me alone, and we decided to continue our research and policy efforts independently.

 

Thus, our partnership with Roth ended in 2007, but the articles we wrote remain, and they have had a tremendous impact. These efforts were crucial in Roth receiving the Economics Nobel Prize in 2012.

 

Utku Ünver: Until 2016, we continued to contribute to the Ohio-based Alliance for Paired Kidney Donation System. They used the software that we had developed for a long time.

 

 

Parentheses: 2012 Nobel Prize in Economics

 

Alvin Roth, in 2012, was awarded the Nobel Prize in Economics along with Lloyd Shapley for their contributions to "stable allocations and the practice of market design." The document that explains the scientific background of the award [22] (pages 28-30) details the previously mentioned studies on kidney exchange. In the conclusion section of the document, the contributions of Abdulkadiroğlu, Pathak, Sönmez, and Ünver are particularly emphasized. It highlights the successful redesign of mechanisms through the in-depth examination of real-world institutions and the identification of issues such as stability and incentives within these institutions.

 

 

 

Could you also describe your efforts to establish a kidney transplantation system in Turkey?

 

Utku Ünver: Between 2016 and 2018, we made intensive efforts to establish a national kidney exchange system in Turkey. Health Minister Recep Akdağ believed in this system and worked hard to establish it. As he was also an academic, he recognized the value of this initiative. In 2017, Recep Akdağ was appointed Deputy Prime Minister, and he continued to support these efforts from his new position.

 

Tayfun Sönmez: We planned to establish the system and handle all the work ourselves, without expecting compensation. We had progressed to the stage of signing a protocol, but it got stuck there, and we don't know what caused it. In 2018, my close friend since childhood, investor Dalınç Arıburnu, stepped in. He offered to cover all the expenses of the patients and donors if such a system were established.[23] Unfortunately, we did not receive a positive or negative response to this proposal either. We see significant challenges in collaboration among different individuals or institutions in Turkey. When our last effort also yielded no results, we decided that establishing a national system in Turkey was beyond our capacity.

 

Up until now, we have been discussing kidney transplantation. Can this entire system also be applied to liver transplantation? What changes?

 

Tayfun Sönmez: The problem is very similar, but a factor in liver transplantation allows us to increase the system's efficiency. First, let me explain the efficiency problem in kidney transplantation.

 

We expected a slight decrease in efficiency in the second system we developed at Delmonico's request, which allowed only 2-way swaps. However, efficiency had decreased by half in practical applications, much larger than we had anticipated. The main problem was that our initial model included all patient-donor pairs, whether compatible or incompatible. This broad participation greatly benefited the system's efficiency. However, the situation was very different in Delmonico's requested second model. Many pairs who would have significantly benefited from participating in the system did not join because they were compatible with their paired donors. For example, consider a pair consisting of a type-A patient and a type-O donor. This pair is not obligated to join the system and chooses not to. However, the type-A patient could receive a kidney from a type-A donor, and receiving a type-O kidney is very wasteful. There are many type-O patients with type A, B, and AB donors waiting for a kidney. When the type-A patient – type-O donor pair does not participate, many type-O patients cannot receive a transplant. In short, this systematic problem leads to a significant loss of efficiency.

 

Utku and I have been brainstorming for years on how to encourage compatible pairs to join the system. We proposed a method that has not yet been implemented and has its own difficulties:

 

After a kidney transplant, the average lifespan of the organ in the patient's body is about 15 years, so even a young patient may need another transplant in the future. For example, there is a pair of a type-A patient and a type-O donor. In the incentive system, if this pair joins and allows for a better match today, in other words, if it saves at least one more life, the patient will be placed at the top of the deceased donor list when they need a kidney transplant in the future.

 

This method can triple the efficiency.[24] The goal is to increase efficiency. Being an economist brings a different perspective here. We are not just optimizing the system but looking for ways to optimize participation. While many articles can be and have been written about a fixed system, we are trying to figure out how to increase participation in the system. In other words, we focus on finding the best solution to a real problem.

 

Some drawbacks may arise in approaches that are based on neo-classical economic principles and that deviate from our ethical-principle-based solutions. An example is a solution led by Alvin Roth and Mike Rees to a problem I mentioned earlier; they proposed importing donors they could not find within the system.

 

Many patients with A donors cannot be matched in an exchange in the system. In 2015, to overcome this problem, Roth and Rees proposed to match them with pairs from countries without good or affordable transplantation technology, such as the Philippines or Mexico.  They called this system global exchange. While traditional cooperation agreements exist between countries, such as among Scandinavian countries, these collaborations involve countries with similar resources and thus consolidate their strength. In the case of the global exchange system, disadvantaged countries can be taken advantage of.

 

When the global exchange system was introduced, ethical objections to this system were raised under the leadership of Delmonico.[25] A working group of the Istanbul Declaration, which was published to combat organ trafficking, organ transplant tourism, and organ trade and to encourage the adoption of effective/ethical organ transplant practices worldwide, issued a separate announcement on the Global Exchange Program.[26] In these publications, concerns were raised that global exchange would lead to organ buying and selling, that it would be difficult to prevent the black market, that the control of patients coming from disadvantaged countries would not be possible, and that they could become victims.

 

With such a reaction, despite all the efforts and resources allocated to the global exchange program, only 52 transplants were carried out between 2015 and 2022. In the same period, the number of transplants performed in the United States using the methods we found exceeded 6,000. This comparison demonstrates the key role of our cautious and ethical approach to solving problems in gaining acceptance for this system worldwide.

 

Why wasn't your proposal to incentivize compatible patient-donor pairs to join the system implemented?

 

Tayfun Sönmez: While entirely ethical and inclusive, our incentive proposal faced a challenge. In the United States, the deceased donor list and the live donor system are separate. Therefore, to implement our proposal and reap these benefits, we would need to intervene in the policies governing the deceased donor list. In other words, we would need to change another policy to achieve this gain, which poses a challenge. This is where we realized that there was a factor in liver transplantation that could also encourage compatible patient-donor pairs to join the system.

 

In a live liver transplant, the donor donates a portion of their liver, either the right or left lobe, as they only have one liver. This is a riskier operation compared to kidney transplantation. Roughly, to ensure the patient does not die during the surgery, at least 40% of the healthy liver must be transplanted. The left lobe accounts for 30-40% of the liver, while the right lobe is 60-70%. Liver transplant patients often have weight problems, and donors are often women with smaller livers. Therefore, donors usually need to donate the larger right lobe. However, when donating the right lobe, there is a significantly higher risk of death and complications compared to donating the left lobe. Consequently, donors naturally prefer to donate the left lobe. So, even though a type-A patient – type-O donor pair is compatible, they are incentivized to join the system for these biological reasons.

 

Considering this aspect of liver transplantation, we believed we could encourage compatible pairs to join the system. We published an article on this system in May 2020, with the collaboration of Haluk Ergin.[27]

 

How did your paths cross with Inonu University?

 

Tayfun Sönmez: When we realized the difficulties of establishing a national kidney exchange system in Turkey and sought a center that would embrace our ideas, liver transplantation came to mind. This endeavor was also academically significant since liver transplants are not commonly performed worldwide. We knew that Turkey was one of the leading countries in liver transplantation, performing about 1,500 transplants annually from live donors. When we learned that Inonu University in Malatya was strong in this field, I sent a long message to Sezai Yılmaz, the Director of the Liver Transplantation Institute, in May 2019. Sezai Yılmaz responded positively to my message and invited me to Malatya.

 

Shortly thereafter, in June, five simultaneous liver transplants, or 10 simultaneous surgeries, were performed at this center. Since the capacity for simultaneous surgeries is critical for exchange systems, this indicated that the physical conditions and human resources at this center allowed for the implementation of swaps involving 5 pairs or fewer. This excited us even more. During my visit to Turkey in July 2019, I visited Sezai Yılmaz and his entire team in Malatya. I convinced them that their institute was one of the most ideal centers in the world to establish a liver exchange system. In September of the same year, we agreed to establish the "Banu Bedestenci Sönmez Liver Paired Exchange System" at the institute.

 

 

 

Utku Ünver: Today, when patients and donors apply to Inonu University Liver Transplantation Institute, their young doctors explain the exchange system and register those who want to participate in the database. They also provide information to compatible patient-donor pairs to encourage them to join the system.

 

Tayfun Sönmez: At this stage, our top priority is to inform patients, who have donors but cannot undergo liver transplantation in Turkey due to blood type incompatibility or mismatched organ (graft) volume, about the program's existence. When all patient-donor pairs are included in the system, many more exchange possibilities become possible.

 

 

The world's first-ever 4-way liver exchange took place in July 2022. Eight surgeries were performed simultaneously and were successfully completed. An article describing both the program and the 4-way exchange, authored by Sezai Yılmaz, Tayfun Sönmez, M. Utku Ünver, Volkan İnce, Sami Akbulut, Burak Işık, and Şükrü Emre, was published in July 2023 under the title "The first 4-way liver exchange resulting from interdisciplinary collaboration between healthcare professionals and design economists."[28]

 

 

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Notes/References

 

1. Utku Ünver’s statement in the interview.

 

2. Afacan, M. O. (2020). What is matching theory? [Translated from Turkish]. Retrieved from https://sarkac.org/2020/01/eslesme-kurami-nedir/

 

3. Scientific Background on the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel 2012, Stable allocations and the practice of market design. Retrieved from https://www.nobelprize.org/uploads/2018/06/advanced-economicsciences2012.pdf

 

 

4. Transdisciplinarity field guide. Retrieved from https://www.uu.nl/en/research/transdisciplinary-field-guide/get-started/what-is-transdisciplinary-research

 

5. Abdulkadiroğlu, A., & Sönmez, T. (1999). House Allocation with Existing Tenants. Journal of Economic Theory, 88(2), 233–260. https://doi.org/10.1006/jeth.1999.2553

 

6. Sönmez, T. and Ünver, M. U. (2005) “House Allocation with Existing Tenants: An Equivalence,” Games and Economic Behavior, 52, 153-185.

 

7. Rapaport, F. T. (1986). The case for a living emotionally related international kidney donor exchange registry. Transplant Proc, 18(3). PMID: 11649919

 

8 & 9. Ross, L. F., & Woodle, E. S. (2000). Ethical issues in increasing living kidney donations by expanding kidney paired exchange programs. Transplantation, 69(7), 1539–1543. https://doi.org/10.1097/00007890-200004270-00001

 

10. Consensus statement on the live organ donor (2000). Retrieved from https://www.kidney.org/sites/default/files/docs/jama_article.pdf

 

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