Costimulatory and Coinhibitory Receptor Control of Alloreactive T Cell Responses

描述(申请人提供)：使用共刺激阻断疗法成功预防移植排斥反应的两个主要障碍是：1)移植前供者反应性记忆T细胞的存在引发急性排斥反应，以及2)CD28阻断背景下EBV特异性免疫受损导致的PTLD。因此，确定克服这些障碍的策略对于优化贝拉奈特在临床上的使用至关重要。我们的初步研究表明，利用新的CD28结构域抗体(DAB)技术选择性地阻断CD28，可以抑制抗CTLA-4 Ig的CD8+突破反应。利用强大的转基因小鼠系统，我们可以在移植后特异性地识别、跟踪和表征CD4+和CD8+供者反应性T细胞，我们已经识别出一种在选择性CD28阻断后特异表达的共抑制分子(2B4，SLAMf4)。2B4在CD28 DAb介导的延长移植物存活中的作用的询问是创新的，因为2B4已被证明在自身免疫和在小鼠和人类的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，2B4在次级CD8+效应器上的表达水平高于初级效应器，最近的一项研究表明，2B4的表达在回忆反应中发挥了抑制CD8+次级效应器的作用。这些耐人寻味的数据提出了一种可能性，即在移植过程中，可以利用这种抑制途径来抑制供者特有的记忆T细胞回忆反应。最后，我们建议直接比较选择性CD28阻断和CTLA-4Ig在对EBV(MHV)小鼠同源物的保护性免疫反应中的效果。最近的一项研究表明，虽然CD80/86-/-动物表现出严重的无法控制MHV复制和从潜伏期重新激活的能力，但CD28-/-动物表现出相当于野生型小鼠的不可检测的病毒载量。这些重要数据表明，选择性阻断CD28可能更好地保存移植后EBV特异性保护性免疫反应。因此，关于在移植过程中选择性阻断CD28的影响，许多问题仍然没有得到回答。在CTLA-4共抑制信号存在的情况下选择性阻断CD28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？鉴于记忆T细胞可能是CTLA-4HI，因此更依赖于这一途径来控制反应，CD28阻断如何对二次回忆反应产生不同的影响？选择性阻断CD28对EBV保护性免疫有何影响？对这些问题的解答将为深入了解共刺激和共抑制受体在移植中的生物学机制提供基础，并将为进一步开发用于临床移植的新型选择性CD28阻滞剂提供机制基础。

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.