Collaborative Research on Kidney Exchange

当希望将肾脏捐赠给特定接受者的人与该接受者不相容时，就会出现换肾的需求。当一个配对中的供者与另一个配对中的受者相容时(或在涉及更多配对配对的周期中)，两个或更多这样不相容的患者-供体对有时都可以通过交换接受移植。部分源于以前由NSF资助的研究，有组织的肾脏交换，如新英格兰肾脏交换计划(NEPKE)在美国变得活跃起来，现在存在并正在增长的多个地区性肾脏交换，以及正在考虑的全国性交换(在2007年通过查理·W·诺伍德活体器官捐赠法案后)。包括许多医院在内的肾脏交换的增长提出了新的实践和理论问题，该奖项资助了在机制设计方面开发新方法来回答这些问题的研究。第一个问题是激励。当肾脏交换计划开始时，第一批模型包含了患者-捐赠者对和他们的外科医生。然而，区域交流的成功表明，移植中心(医院)也必须被纳入战略分析。移植中心处理多个患者-捐赠者对，他们的策略集包括可能不让某些对进行肾脏交换，只揭示那些医院自己无法匹配的对。该团队在实践中确实观察到了这一点，初步研究结果表明，没有办法让医院在仍然使用高效的肾脏交换匹配算法的同时揭示他们的所有配对。其他研究探索了匹配机制在大群体中的激励特性。PIs试图证明现有机制即使在大量人口中也不具有良好的激励特性，但当池中有许多患者-捐赠者对时，可以设计出既具有良好激励特性又具有良好效率特性的替代机制，就像成功的国家交换中的情况一样。PI将Erdos和Rényi(1959,1966)的经典(无向)随机图结果应用于模拟患者-供者对之间的兼容性的图，并使用这些图来探索有许多对的大肾交换的行为。这项工作的第一部分将着眼于患者和捐赠者的一般人群，第二部分将考虑当有大量极度敏感的患者找到捐赠者的可能性较低时产生的不同结构的大型图表。(这将涉及到对兼容性图进行更详细的建模；患者和捐赠者必须有单独的节点，而不是每个患者和她的捐赠者都有一个节点，因为捐赠者的连接性不会受到患者的影响？S说，配合性很低，这样一旦找到这样的肾脏，配对就会很好地联系在一起。)我们还将考虑不同的肾脏交换策略，包括管理可能较长的捐赠链。广泛影响：在美国，有超过8万名患者在等待身体肾脏的名单上。2009年，等待名单上增加了33,678名患者，进行了10,441例身体肾脏移植，4,456名患者在等待名单上死亡，还有1,941名患者因病得太重而被从名单中删除。美国也有6387例活体捐赠者的肾脏移植。可供移植的肾脏严重短缺。近年来，肾脏交换是活体肾脏捐赠者的来源，规模仍然很小，但增长最快。改进配对捐献者和接受者的方法将拯救生命。PIS将与移植中心和地区联盟合作，将新开发的方法投入应用。

The need for kidney exchange arises when someone who wishes to donate a kidney to a particular recipient is incompatible with that recipient. Two or more such incompatible patient-donor pairs can sometimes both receive transplants through an exchange,when the donor in one pair is compatible with the recipient in the other (or in cycles involving more incompatible pairs). Stemming in part from previously funded NSF research, organized kidney exchanges, such as the New England Program for Kidney Exchange (NEPKE) havebecome active in the United States, and now multiple regional kidney exchanges exist and are growing, and a national exchange is being contemplated (following the passage of the Charlie W.Norwood Living Organ Donation Act in 2007). The growth of kidney exchange to include many hospitals has raised new practical and theoretical questions and this award funds research that develops new methods in mechanism design to answer these questions.The first issue is incentives. When kidney exchange programs started, the first models incorporatedpatient-donor pairs and their surgeons. However, the success of regional exchanges has demonstrated that transplant centers (hospitals) must also be included in the strategic analysis. Transplant centers deal with multiple patient-donor pairs, and their strategy sets include the possibility of withholding some pairs from the kidney exchange and revealing only those pairs that the hospital cannot match on its own. The team has observed exactly this in practice, and preliminary research results suggest that there is no way to get hospitals to reveal all their pairs while still using a efficient kidney exchange matching algorithm. Additional research explores the incentive properties of matching mechanisms in large populations. The PIs seek to demonstrate that existing mechanisms do not have good incentive properties even in large populations, but that alternative mechanisms can be designed that would have both good incentives and good efficiency properties when there are many patient-donor pairs in the pool, as would be the case in a successful national exchange.The second part of the project concerns efficiency. The PIs adapt the classical (undirected) random graph results of Erdos and Rényi (1959, 1966) to graphs that model the compatibility between patient-donor pairs, and use these to explore the behavior of large kidney exchanges, with many pairs. The first part of this work will look at general populations of patients and donors, and the second part will consider the differently structured large graphs that result when there is a large population of extremely sensitized patients who have low probability of finding a donor. (This will involve modeling the compatibility graph in more detail; instead of one node for each patient and her donors, there will have to be separate nodes for patients and donors, since the connectedness of donors will be unaffected by the patient?s low probability offinding a compatible kidney, so that, once such a kidney is found, the pair will be well connected.) We will also consider different kidney exchange strategies, including the management of possibly long chains of donations.Broader Impacts: There are over 80,000 patients on the waiting list for cadaver kidneys in the U.S. In 2009, 33,678 patients were added to the waiting list,10,441 transplants of cadaver kidneys were performed, 4,456 patients died while on the waiting list, and more than 1,941 others were removed from the list as ?Too Sick to Transplant?. There were also 6,387 transplants of kidneys from living donors in the US. There is a severe shortage of kidneys for transplant. Kidney exchange is in recent years the still small but fastest growing source of live kidney donors. Improvements in the methods used to match donors and recipients will save lives. The PIs will collaborate with transplant centers and regional alliances to take the newly developed methods into application.