Infections and the Stability of Transplantation Tolerance

计划摘要 移植耐受，移植后对供者抗原长期免疫无反应的状态 停止治疗，是一种具有吸引力的终身接受移植物的方法，而不需要 免疫抑制。对耐受性患者的长期随访显示，有些患者可能会失去耐受性 移植物稳定多年后的个体，有时是在感染之后，增加了两种可能性：耐受性在 诱导同样强劲，但一些患者暴露在更多的炎症事件中，侵蚀了 耐受状态，即在诱导时耐受性在一些患者中是亚稳定的，在另一些患者中是健壮的。 我们计划项目的第一个周期解决了使用鼠标模型的第一种可能性 强大的移植耐受性并能抵抗大多数炎症性挑战，但 单核细胞增多性李斯特菌(Lm)。重要的是，我们通过分析少量的同种异体反应T细胞 同种TCR-TG同种异体反应性T细胞在移植前接种，或使用荧光pMHC I类和 II类多聚体用于鉴定对模型供体抗原有反应的内源性T细胞群体。通过 比较耐受小鼠感染(方案1)和(方案2)LM前后的同种异体反应性T细胞 程序发现，i)移植耐受性由多个冗余机制来维持 T细胞耐受性，包括限制同种异体反应性T细胞数量，增加调节性T细胞与 传统T细胞，内在地抑制传统T细胞，抑制同种异体反应性T细胞群 对同种异体抗原亲和力低的克隆；ii)强大的耐受性是有弹性的，因为它自发地返回到 经历了LM依赖的移植物排斥反应的动物；iii)感染后的耐受性受到侵蚀和依赖 关于T细胞耐受的单一机制，如阻断PD-L1或耗尽Tregs就足以 在感染后耐受宿主中诱发移植物排斥反应，但在未感染宿主中不发生。在全球范围内，我们的计划已经 证明了移植耐受不是一个要么全有要么全不的状态，而是可以存在于不同水平的 健壮性。这些观察结果突显了精确定义和监测潜在机制的必要性 在每一位宽容的接受者中移植接受度，并制定策略，在它变得 被侵蚀了。对于这次竞争性更新，我们将解决第二种可能性，即不是所有患者都能实现 在入职时有很强的耐受性。在整体上，我们假设抑制同种异体反应性T细胞的机制 子集可以区分在幼稚宿主中建立的健壮耐受性和感染后被侵蚀的耐受性，以及 来自致敏宿主的亚稳态或失败耐受性。项目1将重点介绍异种反应的两个新特性 我们最近发现的在幼稚宿主中具有强大移植耐受性的T细胞，即， 细胞固有低反应性和同种异体反应性T细胞对低亲和力克隆的限制项目2将 研究同种异体致敏是诱导移植耐受的主要障碍，如何影响移植耐受的诱导。 T细胞耐受的个体机制，表现为强健的耐受。

PROGRAM SUMMARY Transplantation tolerance, a state of long-lasting immune unresponsiveness to donor antigens after cessation of therapy, is an attractive approach for life-long graft acceptance without global immunosuppression. Long-term follow up of tolerant patients has revealed that tolerance can be lost in some individuals after years of graft stability, sometimes after infections, raising 2 possibilities: that tolerance at induction was equally robust but some patients were exposed to more inflammatory events that eroded the state of tolerance, or that tolerance at induction was metastable in some patients and robust in others. The first cycle of our Program Project addressed the first possibility using a mouse model of transplantation tolerance that is robust and resistant to most inflammatory challenges with the exception of Listeria monocytogenes (Lm). Importantly, we tracked alloreactive T cells by analyzing small numbers of congenic TCR-Tg alloreactive T cells seeded before transplantation, or using fluorescent pMHC Class I and Class II multimers to identify endogenous populations of T cells reactive to model donor antigens. By comparing alloreactive T cells before (Project 1) and after (Project 2) Lm infection of tolerant mice, our Program discovered that i) robust transplantation tolerance is maintained by multiple redundant mechanisms of T cell tolerance, including constraining alloreactive T cell numbers, increasing the ratio of regulatory to conventional T cells, inhibiting conventional T cells intrinsically and restraining alloreactive T cell populations to clones with low avidity for alloantigen; ii) robust tolerance is resilient because it spontaneously returned in animals that experienced Lm-dependent graft rejection; iii) tolerance after infection is eroded and dependent on single mechanisms of T cell tolerance such that blockade of PD-L1 or depletion of Tregs was sufficient to precipitate graft rejection in tolerant hosts post-infection but not in uninfected hosts. Globally, our Program has demonstrated that transplantation tolerance is not an all-or-none state, but rather can exist at different levels of robustness. These observations highlight the need to precisely define and monitor the mechanisms underlying graft acceptance in each tolerant recipient and to devise strategies to improve tolerance when it becomes eroded. For this Competitive Renewal, we will address the second possibility, that not all patients achieve robust tolerance at induction. Globally, we hypothesize that the mechanisms restraining alloreactive T cell subsets can distinguish robust tolerance established in naive hosts from eroded tolerance after infection, and from metastable or failed tolerance in sensitized hosts. Project 1 will focus on 2 novel features of alloreactive T cells that we recently discovered as characteristic of robust transplantation tolerance in naïve hosts, namely, cell intrinsic hyporesponsiveness and the constraint of alloreactive T cells to low avidity clones Project 2 will study how allosensitization, a major barrier to the induction of transplantation tolerance, affects the induction of the individual mechanisms of T cell tolerance that characterize robust tolerance.