Role of TIGIT Signaling in Transplantation

总结。移植是终末期器官衰竭的根治疗法，但其发病率很高。 由于免疫抑制引起的毒性导致的移植物损失仍然高得令人无法接受。Ballatacept，CTLA-4Ig 融合蛋白是20多年来移植免疫抑制的第一种新疗法，提供了一种 对肾移植受者有很大的好处，因为它降低了43%的死亡或移植后丢失的风险 与以钙调神经磷酸酶抑制剂为基础的方案相比，已持续数年。然而，拉帕西汀显著地赋予了 与钙调神经磷酸酶抑制剂相比，急性排斥反应的风险增加。有两个主要的蜂窝子集 1)Foxp3+Treg和2)CD8+记忆性T细胞参与了耐药排斥反应。第一, 大量研究表明，由于belatacept/CTLA-4Ig与CTLA-4的CD80/86配体结合， CTLA-4介导的Treg的抑制功能在这些条件下受到损害。第二，一个 单独的研究表明，不同的CD8+记忆性T细胞群体的需求有所降低 用于CD28共刺激。在小鼠、NHP和人类中的研究已经确定了CD8+同种异体反应性T细胞 因为在移植过程中形成了移植接受的障碍。因此，确定满足以下条件的替代路径1) CTLA-4阻断增强Treg抑制功能和2)控制记忆CD8+T细胞 排斥或耐受期间的人群是移植中的临床相关问题。我们的预赛 数据显示，虽然TIGIT的激动剂单独对移植物存活没有影响，但TIGIT的激动剂减轻了移植物的存活率 在CTLA-4Ig治疗的环境中观察到的协同刺激阻断抵抗排斥反应，导致 延长同种异体移植物存活时间。然而，这些观察结果背后的机制尚不清楚。 在CTLA-4Ig的背景下，TIGIT激动症对Tregs的影响是什么？什么是细胞和分子？ Tregs上TIGIT激动剂下游的途径？TIGIT激动剂在记忆中是否有细胞固有的作用 CD8+T细胞在CTLA-4Ig？Foxp3+Treg的TIGIT激活对记忆CD8+T细胞的影响 细胞？培拉泰塞对移植受者分离的人T细胞有何影响？ 小路？在这项建议中，我们将分析TIGIT激动剂对Foxp3+Treg(可能 继而影响移植物反应性CD8+T细胞反应)和CD8+记忆性T细胞的细胞固有效应 在Foxp3+Treg或记忆性CD8+T细胞上使用TIGIT的条件敲除。这项建议将会解决 这些基本问题，从而填补了我们目前对TIGIT共抑制作用的理解的空白 在移植过程中的T细胞同种免疫。最后，我们建议直接测试这些指标的临床相关性。 询问TIGIT激动剂对Foxp3+Treg和CD8+的影响的发现和假说 从培拉泰普治疗的人肾移植受者中分离出效应/记忆T细胞。了解 TIGIT信号传递克服抗拉他赛普排斥的机制将提供重要的 信息，以优化使用贝拉塔塞特用于临床移植。

Summary. Transplantation is a curative treatment for end-stage organ failure, but rates of significant morbidity and graft loss due to immunosuppression-induced toxicities remain unacceptably high. Belatacept, a CTLA-4Ig fusion protein and the first new therapy for immunosuppression in transplantation in over 20 years, offers a significant benefit to renal transplant recipients in that it carries a 43% reduced risk of death or graft loss after 7 years as compared to calcineurin inhibitor-based regimens. However, belatacept confers a significantly increased risk of acute rejection as compared to calcineurin inhibitors. The two main cellular subsets that have been implicated in belatacept-resistant rejection are 1) Foxp3+ Treg and 2) CD8+ memory T cells. First, numerous studies have shown that because belatacept/CTLA-4Ig binds to the CD80/86 ligands for CTLA-4, the CTLA-4-mediated suppressive function of Treg is compromised under these conditions. Second, a separate body of work has shown that distinct CD8+ memory T cell populations exhibit reduced requirements for CD28 costimulation. Studies in mouse, NHP, and humans have identified CD8+ alloreactive memory T cells as forming a barrier to graft acceptance during transplantation. As such, identifying alternate pathways that 1) augment Treg suppressive function in the context of CTLA-4 blockade and 2) control memory CD8+ T cell populations during rejection or tolerance are clinically relevant questions in transplantation. Our preliminary data show that that while agonism of TIGIT alone had no effect on graft survival, agonism of TIGIT mitigated the costimulation blockade-resistant rejection observed in the setting of treatment with CTLA-4Ig, resulting in prolonged allograft survival. However, the mechanisms underlying these observations are not understood. What is the impact of TIGIT agonism on Tregs in the context of CTLA-4Ig? What are the cellular and molecular pathways downstream of TIGIT agonism on Tregs? Is there a cell-intrinsic role for TIGIT agonism on memory CD8+ T cells in the context of CTLA-4Ig? How does TIGIT agonism of Foxp3+ Treg impact memory CD8+ T cells? What is the impact of belatacept treatment of human T cells isolated from transplant recipients on these pathways? In this proposal, we will parse apart the effect of TIGIT agonism on Foxp3+ Treg (which could secondarily impact graft-reactive CD8+ T cell responses) and a cell-intrinsic effect on CD8+ memory T cells using conditional knockouts of TIGIT on either Foxp3+ Treg or memory CD8+ T cells. This proposal will answer these fundamental questions, thereby filling a gap in our current understanding of the role of TIGIT coinhibition in T cell alloimmunity during transplantation. Finally, we propose to directly test the clinical relevance of these findings and hypotheses by interrogating the impact of TIGIT agonism on both Foxp3+ Treg and CD8+ effector/memory T cells isolated from belatacept-treated human renal transplant recipients. Understanding the mechanisms by which TIGIT signaling overcomes belatacept-resistant rejection will provide important information to optimize the use of belatacept for use in clinical transplantation.