Elucidating the Immune Suppressive Mechanism of SIGLEC-15 in the Tumor Microenvironment

阻断免疫检查点PD-1/PD-L1（PD）通路的免疫调节剂已显示出显著的 临床益处，并构成癌症治疗的新护理标准。这些代理商的成功是由于 PD-1受体的突出免疫抑制功能及其选择性表达， 配体PD-L1在肿瘤微环境（TME）中的作用，导致有利的疗效与毒性比。然而，在这方面， 尽管抗PD治疗提供了巨大的进步，但只有一部分患者产生了长期反应， 这说明需要在TME中，特别是在PD-L1阴性肿瘤中鉴定新的免疫调节剂。到 为了实现这一目标，我们建立了第一个人类膜蛋白的基因组规模的T细胞活性筛选，并鉴定了 Siglec-15是一种关键的免疫抑制剂，对各种癌症类型具有广泛的上调作用，是治疗癌症的新靶点。 癌症免疫疗法Siglec-15与许多其他已知的检查点相比具有独特的分子特征 抑制配体。除了肿瘤相关巨噬细胞外，它还在癌细胞上显示出优势表达， 在人类癌症中表现出PD-L1互斥表达模式。通过单克隆抗体阻断Siglec-15 抗体在小鼠肿瘤模型和人癌细胞培养系统中显示治疗功效， T细胞反应增强Siglec-15可能代表一类新的免疫检查点配体， PD-L1的相关表达和不同的作用机制，对抗PD具有重要意义 无反应的病人基于这些结果，我们开发了抗人Siglec-15抗体（NC 318）。 目前正在进行的PD-1难治性转移性实体癌的相关I/II期临床试验。虽然 初步的临床试验结果是非常有希望的，明确阐明了免疫抑制作用， 研究Siglec-15在肿瘤微环境中的作用机制将推动这一新方案的临床转化。 除了调节T细胞功能外，我们的新发现还表明Siglec-15代表了一种潜在的新功能， 髓样细胞的控制轴，髓样细胞是塑造肿瘤微环境的关键免疫细胞亚群， 相对缺乏成功的临床靶点。除此之外，重要的问题仍然是优化Siglec-15- 相关治疗，如其受体、诱导机制和潜在的累加效应或协同作用， 现有的治疗。在这个项目中，通过两个互补的目标，我们将利用我们在癌症方面的专业知识， 免疫学和免疫疗法，以：1）确定Siglec-15在T细胞之外的潜在免疫功能， 特别是骨髓细胞上的Siglec-15受体，并表征骨髓细胞和T细胞上的功能性Siglec-15受体; 2)检查致癌KRAS突变体作为Siglec-15表达对癌症的诱导机制的作用 细胞和确定更好的抗Siglec-15组合疗法，使用两种致癌KRAS突变相关的 胰腺癌和卵巢癌的同基因原位小鼠模型。总的来说，我们提出的研究将 促进我们对新型PD-L1互斥免疫检查点的理解，并增强Siglec-15- 基于抗PD-1/PD-L1不敏感癌症的治疗方法。

Immunomodulatory agents blocking the immune checkpoint PD-1/PD-L1 (PD) pathway have shown remarkable clinical benefits and constitute a new standard of care for cancer treatment. The success of these agents is due to the prominent immunosuppressive function of the PD-1 receptor alongside the selective expression of its ligand, PD-L1, in the tumor microenvironment (TME), leading to a favorable efficacy-to-toxicity ratio. However, despite the vast advances provided by anti-PD therapy, only a subset of patients develops a long-term response, illustrating the need for identifying new immune modulators in the TME, especially in PD-L1 negative tumors. To achieve this, we built the first genome-scale T-cell activity screen of human membrane proteins and identified Siglec-15 as a critical immune suppressor with broad upregulation on various cancer types and a new target for cancer immunotherapy. Siglec-15 has unique molecular features compared with many other known checkpoint inhibitory ligands. It shows dominant expression on cancer cells, besides tumor-associated macrophages, and exhibits PD-L1 mutually exclusive expression pattern in human cancers. Siglec-15 blockade by a monoclonal antibody shows therapeutic efficacy in mouse tumor models and human cancer cell culture systems and results in amplified T cell responses. Siglec-15 may represent a novel class of immune checkpoint ligands with tumor- associated expression and divergent mechanisms of action to PD-L1, with important implications for anti-PD unresponsive patients. Based on these results, we have developed an anti-human Siglec-15 antibody (NC318) with the related phase I/II clinical trials currently ongoing for PD-1 refractory metastatic solid cancers. Although the preliminary clinical trial results are quite promising, the clear elucidation of the immune suppressive mechanism of Siglec-15 in the tumor-microenvironment will advance the clinical translation of this novel program. Other than modulating T cell function, our new findings also suggest that Siglec-15 represents a potential novel axis of control for myeloid cells, a key immune cell subset critical in shaping the tumor microenvironment which have a relative lack of successful clinical targets. Beyond this, important questions remain to optimize Siglec-15- related therapy, such as its receptor(s), induction mechanisms, and potential additive effects or synergies with existing treatments. In this project, through two complementary aims, we will leverage our expertise in cancer immunology and immunotherapy to: 1) determine the potential immune function of Siglec-15 beyond T cells, particularly on myeloid cells, and to characterize functional Siglec-15 receptors on both myeloid cells and T cells; 2) examine the role of oncogenic KRAS mutants as induction mechanism of Siglec-15 expression on cancer cells and identify better anti-Siglec-15 combinatorial therapies using two oncogenic KRAS mutant-associated syngeneic orthotopic mouse models of pancreatic and ovarian cancer. Collectively, our proposed studies will facilitate our understanding of a novel PD-L1 mutually exclusive immune checkpoint and enhance Siglec-15- based therapeutic approaches for anti-PD-1/PD-L1 insensitive cancers.