Costimulatory and Coinhibitory Receptor Control of Alloreactive T Cell Responses

描述（由申请人提供）：使用基于共刺激阻断的治疗成功预防移植排斥的两个主要障碍是：1）移植前存在供体反应性记忆T细胞，其会引发急性排斥反应; 2）在CD 28阻断的情况下，EBV特异性免疫受损导致PTLD。因此，确定克服这些障碍的策略对于优化贝拉西普在临床中的使用至关重要。我们的初步研究表明，CTLA-4 Ig-抗性CD 8+突破反应被使用新型CD 28结构域抗体（dAb）技术的选择性CD 28阻断所抑制。使用强大的转基因小鼠系统，我们可以特异性地识别，跟踪和表征移植后的CD 4+和CD 8+供体反应性T细胞，我们已经确定了一种共抑制分子（2B 4，SLAMf 4），它在选择性CD 28阻断后特异性表达。探究2B 4在CD 28 mAb介导的移植物存活延长中的作用是创新的，因为2B 4已被证明在小鼠和人类的自身免疫和慢性病毒感染中发挥重要作用，但以前从未在移植中进行过研究。有趣的是，2B 4在次级CD 8+效应子上的表达水平高于初级效应子，最近的一项研究表明，2B 4的表达在回忆反应期间抑制CD 8+次级效应子中起着功能性作用。这些有趣的数据提出了这种抑制途径可以用来抑制移植过程中供体特异性记忆T细胞回忆反应的可能性。最后，我们建议直接比较选择性CD 28阻断与CTLA-4 IG对EBV（MHV）小鼠同源物的保护性免疫应答的影响。最近的一项研究表明，虽然CD 80/86-/-动物表现出严重的无法控制MHV复制和潜伏期的再激活，但CD 28-/-动物表现出与野生型小鼠相当的不可检测的病毒载量。这些重要的数据表明，选择性CD 28阻断可以更好地保护移植后的EBV特异性保护性免疫反应。因此，关于移植期间选择性CD 28阻断的影响，许多问题仍然没有答案。在CTLA-4共抑制信号存在的情况下，选择性CD 28阻断如何影响其他共刺激和共抑制分子的表达以改变T细胞编程？考虑到记忆T细胞可能是CTLA-4 hi，因此更依赖于这一通路来控制反应，CD 28阻断如何不同地影响二次回忆反应？选择性CD 28阻断对EBV保护性免疫有什么影响？这些问题的答案将提供基本的见解，共刺激和共抑制受体在移植的生物学，并将提供一个机制基础，为进一步开发新的选择性CD 28阻滞剂用于临床移植。

DESCRIPTION (provided by applicant): Two major obstacles to successful prevention of transplant rejection using costimulation blockade-based therapy are 1) the presence of donor-reactive memory T cells prior to transplantation that precipitate acute rejection, and 2) PTLD resulting from compromised EBV-specific immunity in the setting of CD28 blockade. Thus, the identification of strategies to overcome these obstacles is of critical importance in order to optimize the use of belatacept in the clinic. Our preliminary studies revealed that CTLA-4 Ig-resistant CD8+ breakthrough responses are inhibited by selective CD28 blockade using novel CD28 domain antibody (dAb) technology. Using powerful transgenic murine systems in which we can specifically identify, track, and characterize both CD4+ and CD8+ donor-reactive T cells following transplantation, we have identified a coinhibitory molecule (2B4, SLAMf4) that is specifically expressed following selective CD28 blockade. Interrogating the role of 2B4 in CD28 dAb-mediated prolongation of graft survival is innovative in that 2B4 has been shown to play an important role in autoimmunity and in chronic viral infections in both mice and humans, yet has never before been studied in transplantation. Interestingly, 2B4 is expressed at increased levels on secondary CD8+ effectors relative to primary effectors, and a recent study demonstrated that the expression of 2B4 plays a functional role in inhibiting CD8+ secondary effectors during recall responses. These intriguing data raise the possibility that this inhibitory pathway could be harnessed to inhibit donor-specific memory T cell recall responses during transplantation. Finally, we propose to directly compare the effects of selective CD28 blockade vs. CTLA-4 Ig on protective immune responses to a murine homolog of EBV (MHV). A recent study revealed that while CD80/86-/- animals exhibited a profound inability to control MHV replication and reactivation from latency, CD28-/- animals exhibited undetectable viral loads equivalent to wild-type mice. These important data suggest that selective CD28 blockade may better preserve EBV-specific protective immune responses following transplantation. Thus, many questions remain unanswered with regard to the impact of selective CD28 blockade during transplantation. How does selective CD28 blockade in the presence of CTLA-4 coinhibitory signals impact the expression of other costimulatory and coinhibitory molecules to alter T cell programming? How does CD28 blockade differentially impact secondary recall responses, given the fact that memory T cells may be CTLA-4hi and therefore more reliant on this pathway for control of the response? What is the impact of selective CD28 blockade on protective immunity to EBV? Answers to these questions will provide fundamental insights into the biology of costimuatory and coinhibitory receptors in transplantation, and will provide a mechanistic foundation for the further development of novel selective CD28 blockers for use in clinical transplantation.