GVL Resistance: Immune selection, T cell ignorance and T cell exhaustion

供体T细胞在异基因造血干细胞移植（alloSCT）中起着至关重要的作用。首先,na ?T细胞和病原体特异性供体记忆T细胞（TM）保护受体免受感染。其次，供体T细胞介导移植物抗白血病（GVL）效应。在mhc匹配的同种异体移植中，gvl诱导T细胞靶向次要组织相容性抗原（miHAs）。不幸的是，miha反应性T细胞也会攻击非恶性宿主组织，导致移植物抗宿主病（GVHD）。长期以来，一个难以实现的目标是开发一种方法，既能保持GVL和免疫重建，又能最大限度地减少GVHD。第二个目标是克服GVL抗性。事实上，复发性疾病是移植后死亡的最大原因。白血病复发必须与同种异体反应性T细胞、白血病细胞和宿主的特性有关。了解这些因素是如何导致复发的，需要临床相关的模型，其中每种影响都可以分离出来。了解复发的一个主要障碍是无法在具有所有（甚至少数）导致GVL的同种异体特异性的多克隆T细胞中进行追踪。第二个障碍是缺乏临床相关和基因可操纵的白血病。我们有了新的数据，揭示了在一个容易追踪的多克隆gvl诱导T细胞靶向相关的和基因可操纵的白血病的模型中，面对强效同种免疫的白血病复发之间的脱节。我们假设，如果在供体中诱导CD8+ TM对白血病细胞表达的miHAs反应，GVL将会增强。正如我们所希望的那样，来自miha疫苗供者的CD8+ TM是GVL的有效介质，可以对抗由bcr-abl和NUP98-HOXA9融合cdna的逆转录病毒转移诱导的抗GVL细胞危象性CML （bc -CML）模型。MiHA特异性TM急剧扩张。然而，相当一部分小鼠死于mBC-CML。这是非常出乎意料的，特别是进行性mBC-CML小鼠保留了大量的miHA反应性CD8细胞。我们将使用该模型来检验关于GVL耐药的两个非排他性假设：1)对GVL耐药白血病亚克隆的同种免疫选择；2) T细胞反应受到T细胞外源性或内源性因素的限制。我们的系统具有独特的优势，使其成为这些研究的理想选择。使用MHCI四聚体，我们可以追踪micha特异性多克隆T细胞，这是介导GVL的唯一T细胞。mBC- CML是人类BC-CML/AML的种族和表型，由于它是由逆转录病毒诱导的，我们可以很容易地创建基因修饰白血病。我们还组装了阻断T细胞抑制途径的关键基因修饰小鼠和试剂。这些研究解决了一个真正的临床问题。我们正在进行一项临床试验，其中白血病患者接受cd34选择的移植物，补充TM，通过使用PI共同开发的试剂耗尽CD45RA+ TN纯化。在随后的研究中，我们计划纳入供体miha疫苗接种。这些研究将通过这种方法确定GVL的耐药机制，类似的耐药机制可能在没有供体疫苗接种的同种免疫反应中发挥作用。

DESCRIPTION (provided by applicant): Donor T cells play a vital role in allogeneic hematopoietic stem cell transplantation (alloSCT). First, na?ve and pathogen-specific donor memory T cells (TM) protect recipients from infection. Second, donor T cells mediate the graft-versus leukemia (GVL) effect. In MHC-matched alloSCT, GVL-inducing T cells target minor histocompatibility antigens (miHAs). Unfortunately, miHA-reactive T cells also attack nonmalignant host tissues, causing graft-vs-host disease (GVHD). A longstanding and elusive goal has been to develop approaches that preserve GVL and immune reconstitution while minimizing GVHD. A second goal is to overcome GVL- resistance. Indeed, relapsed disease is the greatest cause of post-transplant mortality. Leukemia relapse must relate to properties of alloreactive T cells, leukemia cells and the host. Understanding how these contribute to relapse requires clinically relevant models in which effects of each can be isolated. A major barrier to understanding relapse has been an inability to track among polyclonal T cells with all (or even a few) of the allospecificities that contribute to GVL. A second obstacle has been the lack of clinically relevant and genetically manipulable leukemias. We have new data that shed light on the disconnect between leukemia relapse in the face of potent alloimmunity in a model wherein easily trackable polyclonal GVL-inducing T cells target a relevant and genetically manipulable leukemia. We hypothesized that GVL would be augmented if CD8+ TM reactive against miHAs expressed by leukemia cells were induced in the donor. As we hoped, the CD8+ TM from miHA-vaccinated donors were potent mediators of GVL against a GVL-resistant model of blast crisis CML (mBC-CML) induced by the retroviral transfer of bcr-abl and NUP98-HOXA9 fusion cDNAs. MiHA- specific TM underwent dramatic expansion. However, a substantial fraction of mice succumbed to mBC-CML. This was quite unexpected, especially as mice with progressive mBC-CML retained a large number of miHA- reactive CD8 cells. We will use this model to test two nonexclusive hypotheses regarding GVL resistance: 1) alloimmunity selects for GVL-resistant leukemia subclones; and 2) the T cell response is restricted by T cell- extrinsic or -intrinsic factors. Our system has unique strengths that make it ideal for these studies. Using MHCI tetramers we can track the miHA-specific polyclonal T cells which are the only T cells that mediate GVL. mBC- CML is genocopy and phenocopy of human BC-CML/AML and because it is induced by retrovirus, we can readily create gene-modified leukemias. We have also assembled key gene-modified mice and reagents that block T cell inhibitory pathways. These studies address a real clinical concern. We have an ongoing clinical trial wherein leukemia patients receive CD34-selected grafts supplemented with TM purified by the depletion of CD45RA+ TN using a reagent co-developed by the PI. In a subsequent study we plan to incorporate donor miHA-vaccination. These studies will identify GVL resistance mechanisms with this approach and similar resistance mechanisms are likely in play in alloimmune responses without donor vaccination.