Strategies for Receptor inhibition in immunotherapy

摘要： 尽管最近在免疫治疗方面取得了进展，如封锁检查站，但激进的新方法正在 既要提高现有治疗的有效性，又要提供全新的治疗方式。在……里面 在这个奖项的前一期，我们开发了一种免疫治疗剂，它利用了髓系分支 免疫系统通过阻断SIRPA/CD47轴，增强巨噬细胞对肿瘤的攻击。我们 设计了一种独特的、高亲和力的CD47 SIRPA拮抗剂，极大地增强了 几种临床批准的抗肿瘤抗体，但提供的优势是肿瘤选择性和非 毒性，这是目前大多数抗CD47单抗的局限性。这种分子目前正在进行几项临床试验 癌症类型，从而在一个任期内完成了从板凳到床边的循环。在此续签申请中， 我们请求支持在肿瘤学中开发受体抑制的新范例。我们提出了一种新的方法 免疫检查点封锁(ICB)，并通过利用未开发的 抑制免疫受体信号的自然生物学机制。我们发现， 包含ITIM/ITAM/ITSM/ITTM的免疫受体，如检查点受体PD1和CTLA4 在没有配基结合的情况下发出信号。因此，阻断PD-L1与抗PD1抗体的结合确实 T细胞激活未完全“刹车”：非配体依赖的PD1强直信号显著钝化 T细胞活化。我们设计了一种减少或消除紧张性信号的策略，称为受体抑制，通过 磷酸酶募集(RIPR)，依赖于激酶介导的信号受体与细胞的顺式连接 表面磷酸酶，如CD45，通过细胞内实现完全的信号抑制 细胞内靶受体ITAM/ITIM/ITSM/ITTM结构域去磷酸化。RIPR分子是双- 迫使靶受体二聚化为细胞表面磷酸酶的特异性抗体，抑制两者 配基结合和紧张性信号。使用PD1系统作为我们的第一个目标，我们发现我们实现了显著的 使用RIPR更大程度地抑制检查点封锁，RIPR使PD1与T细胞磷酸酶CD45二聚化， 而不是用抗PD1抗体阻断配体。此外，我们看到治疗效果增强超过了抗- PD1在几种小鼠肿瘤模型中的表达。在这项建议中，我们寻求支持，以更好地理解 在生化和细胞水平上的RIPR，以评估其在一系列小鼠肿瘤模型中的治疗效果 单独和与治疗性抗体结合使用，并探索检查点以外的RIPR应用 抑制其他受体，如CTLA4和SIRPA，这是肿瘤药物的靶点。

Abstract: Despite the recent advances in immunotherapy, such as checkpoint blockade, radical new approaches are needed to both improve the efficacy of existing treatments, and to offer entirely new therapeutic modalities. In the previous term of this award we developed an immunotherapeutic agent that exploited the myeloid branch of the immune system by blocking the SIRPa/CD47 axis, potentiating macrophage attack on tumors. We engineered a unique, high-affinity SIRPa antagonist of CD47 that greatly potentiated the anti-tumor efficacy of several clinically approved anti-tumor antibodies, yet offered the advantage of being tumor selective and non- toxic, which is a limitation of most current anti-CD47 mAbs. This molecule is now in clinical trials for several cancer types, thus completing the cycle of bench to bedside in one term of the award. In this renewal application, we request support to develop a new paradigm for receptor inhibition in oncology. We present a new approach to immune checkpoint blockade (ICB), and antagonizing the CD47/SIRPa axis, by exploiting an untapped natural biological mechanism for dampening immune receptor signaling. We have found that ITIM/ITAM/ITSM/ITTM-containing immunoreceptors, such as the checkpoint receptors PD1 and CTLA4, tonically signal in the absence of ligand engagement. As a result, blocking PD-L1 binding with anti-PD1 antibodies, does not fully “take the brakes off” of T cell activation: ligand-independent PD1 tonic signaling significantly blunts T cell activation. We have devised a strategy reduce or eliminate tonic signaling, termed Receptor Inhibition by Phosphatase Recruitment (RIPR), that relies on the cis-ligation of kinases-mediated signaling receptors to a cell surface phosphatase, such as CD45, to achieve complete signal inhibition through intracellular dephosphorylation of the target receptor intracellular ITAM/ITIM/ITSM/ITTM domains. RIPR molecules are bi- specific antibodies that compel dimerization of a target receptor to a cell-surface phosphatase, inhibiting both ligand binding and tonic signaling. Using the PD1 system as our first target, we find that we achieve significantly greater inhibition of checkpoint blockade using a RIPR that dimerizes PD1 with the T cell phosphatase CD45, versus ligand blocking by anti-PD1 antibodies. Furthermore, we see enhanced therapeutic efficacy over anti- PD1 in several mouse tumor models. In this proposal we seek support to better understand the mechanism of RIPR at the biochemical and cellular level, to assess its therapeutic efficacy in a range of mouse tumor models both alone and in combination with therapeutic antibodies, and to explore RIPR applications beyond checkpoint inhibition to other receptors, such as CTLA4 and SIRPa, that are oncology drug targets.