B7-based, CD28 or CTLA-4-specific agonists and antagonists for tolerance inductio

描述（由申请人提供）：同种异体造血细胞移植（HCT）是一种治疗危及生命的非恶性造血和免疫系统疾病的有效疗法，如骨髓衰竭综合征、血红蛋白病、免疫缺陷疾病和溶酶体贮积病。在非恶性疾病患者中，同种异体HCT的主要局限性是宿主抗移植物反应（移植物排斥）和供体淋巴细胞对宿主抗原的免疫反应，也称为移植物抗宿主病（GVHD），这两种反应都可能是致命的。为了避免移植物排斥和GVHD的问题，同种异体HCT接受者通常用免疫抑制剂的组合治疗延长的时间段。然而，长期的免疫抑制也会削弱宿主对病原体的免疫反应，从而增加严重感染的风险，并且在控制GVHD方面并不总是成功的。因此，需要在不损害免疫能力的情况下促进免疫耐受的努力来改善HCT的结果。CD 28和CTLA-4是白细胞表面共刺激受体，深刻影响免疫应答的过程：CD 28放大TCR信号传导的作用，并增强细胞周期进展和T细胞存活; CTLA-4（CD 152）提供相反的抑制信号。CD 28和CTLA-4结合共有的相关配体B7.1（CD 80）和B7.2（CD 86）。该项目的长期目标是开发合理的工程化拮抗剂和激动剂， CD 28或CTLA-4在各种临床环境中用作短期免疫治疗剂，最初专注于控制同种异体HCT后的宿主抗移植物反应和GVHD。我们的假设是，在移植后不久施用CD 28拮抗剂沿着CTLA-4激动剂应导致宿主和供体T细胞的下调，所述宿主和供体T细胞响应于错配的主要和次要抗原而特异性活化，防止募集并诱导新活化的T细胞的凋亡。理想的试剂将对CD 28或CTLA-4具有最大的选择性，具有短的生物半衰期以减少免疫相关的不良事件，并且具有最小的分子量以最大化组织迁移率。该项目（该R21应用）的探索/开发阶段的直接目标是通过计算将B7.1和B7.2的可溶形式重新设计为受体特异性结合试剂，确认其生物化学性质，接下来将在随后的合作应用中在基于体外细胞的测定和体内研究（在组织相容性骨髓移植的犬模型中）中进行评价。这些试剂的小尺寸优化了组织渗透率和短的生物半衰期;我们预测单体形式将作为竞争性拮抗剂， 多聚体（二聚体Fc融合物或四价试剂）将充当激动剂。这种方法利用了我们成功建立的迭代蛋白质工程管道，用于开发基于新型B7重新设计靶标的计算设计的AIDS疫苗免疫原（“表位支架”），用于独特的治疗应用。 公共卫生相关性：异基因造血细胞移植（HCT）已用于治疗危及生命的非恶性疾病（骨髓衰竭综合征、血红蛋白病和造血和免疫系统的其他遗传性疾病），但急性和慢性移植物抗宿主病（GVHD）仍然是HCT后治疗失败的主要原因。我们建议开发计算重新设计的分子（B7.1和B7.2的受体选择性版本）作为短期免疫治疗剂，通过靶向共刺激受体CD 28和CTLA-4并操纵其信号输出，在不损害免疫能力的情况下促进免疫耐受。从长远来看，这种方法也可以使患有自身免疫性疾病的患者和接受实体器官移植的患者受益;此外，它将为造血和实体器官移植的联合移植奠定基础，从而消除实体器官移植受者终身免疫抑制治疗的需要。

DESCRIPTION (provided by applicant): Allogeneic hematopoietic cell transplantation (HCT) is an effective therapy for life-threatening, non-malignant disorders of the hematopoietic and immune systems, such as marrow failure syndromes, hemoglobinopathies, immunodeficiency disorders and lysosomal storage diseases. Major limitations of allogeneic HCT in patients with nonmalignant disorders have been host-versus-graft reactions (graft rejection) and immune reactions of donor lymphocytes against host antigens, also called graft-versus-host disease (GVHD), both of which can be fatal. To circumvent the problems of graft rejection and GVHD, allogeneic HCT recipients are generally treated with combinations of immunosuppressive agents for extended periods of time. Long term immunosuppression, however, also weakens host immune responses to pathogens, thereby increasing the risk of serious infections - and is not uniformly successful in controlling GVHD. Therefore, efforts at promoting immune tolerance without compromising immune competence are needed to improve outcomes in HCT. CD28 and CTLA-4 are leukocyte cell-surface costimulatory receptors that profoundly influence the course of immune responses: CD28 magnifies the effects of TCR signaling and enhances both cell cycle progression and T cell survival; CTLA-4 (CD152) provides opposing inhibitory signals. CD28 and CTLA-4 bind the shared, related ligands B7.1 (CD80) and B7.2 (CD86). The long-term goal of this project is to develop rationally engineered antagonists and agonists specific for CD28 or CTLA-4 for use as short-term immunotherapeutics in various clinical contexts, initially focusing on the control of host-versus-graft reactions and GVHD following allogeneic HCT. Our hypothesis is that administering a CD28 antagonist along with a CTLA-4 agonist shortly after transplantation should lead to down-regulation of both host and donor T cells that were specifically activated in response to mismatched major and minor antigens, prevent recruitment and induce apoptosis in newly activated T cells. Ideal reagents would be maximally selective for CD28 or CTLA-4, have short biological half-lives to reduce immune related adverse events and minimal molecular weights to maximize tissue penetrance. The immediate goal of the exploratory/developmental phase of this project (this R21 application) is to computationally redesign soluble forms of B7.1 and B7.2 into receptor-specific binding reagents, confirming their properties biochemically, that would next be evaluated in in vitro cell-based assays and in vivo studies (in the canine model of histocompatible marrow transplantation) in subsequent collaborative applications. The small size of these reagents optimizes tissue penetrance and short biological half-life; we predict that monomeric forms will act as competitive antagonists and that multimeric (dimeric Fc fusions or tetravalent reagents) will act as agonists. This approach leverages an iterative protein engineering pipeline we successfully established for the development of computationally-designed AIDS vaccine immunogens ("epitope-scaffolds") for a distinct therapeutic application based on novel B7 redesign targets. PUBLIC HEALTH RELEVANCE: Allogeneic hematopoietic cell transplantation (HCT) has been used to treat life-threatening non-malignant disorders (marrow failure syndromes, hemoglobinopathies and other inherited diseases of the hematopoietic and immune systems), but acute and chronic graft-versus-host disease (GVHD) remain major causes of treatment failure after HCT. We propose to develop computationally-redesigned molecules (receptor-selective versions of B7.1 and B7.2) as short-term immunotherapeutics to promote immune tolerance without compromising immune competence, by targeting the costimulatory receptors CD28 and CTLA-4 and manipulating their signaling outputs. In the long term, this approach could also benefit patients with autoimmune diseases and those undergoing solid organ transplantation; in addition, it would set the stage for combined transplantations of hematopoietic and solid organ grafts, thereby eliminating the need for life-long immunosuppressive treatment in solid organ graft recipients.