ST8Sia6 expression on tumors inhibits the immune response

检查点阻断，其目标是抑制T细胞对肿瘤的成功反应的抑制受体， 展示了免疫反应在抗癌中发挥的关键作用。然而，并不是所有的癌症 对针对T细胞上PD-1或CTLA-4的免疫治疗或检查点阻断有反应。例如， 大多数结肠癌患者对检查点抑制剂单一疗法没有反应，这种疗法对 只有4%的患者存在微卫星不稳定性。因此，许多肿瘤可能针对其他抑制性受体或 免疫系统的不同组成部分，以阻止它建立有效的反应。一个家庭 免疫细胞上的抑制受体是Siglec家族，它识别唾液酸修饰的配体 细胞表面的糖蛋白或糖脂。有20种真核唾液酸转移酶，每一种都是 在它们的首选连接、目标和添加的唾液酸数量上不同。人们很早就认识到 肿瘤改变了细胞表面糖基化和唾液酸的类型和频率。特别是，增加了 在癌症中经常观察到唾液酸的掺入，尽管高唾液酸化在癌症中的作用 促进和维持肿瘤生长的机制还不是很清楚。有趣的是，使用宇宙数据库，我们 研究发现，虽然389个人类肿瘤过度表达唾液酸转移酶ST8Sia6，但没有一个肿瘤表达不足 ST8Sia6；这表明对高ST8Sia6的肿瘤具有很强的选择性优势，尽管ST8Sia6的功能 ST8Sia6在癌症中的作用尚不清楚。我们证明了ST8Sia6在MC38或B16-F10中过表达 肿瘤细胞系加速了小鼠的肿瘤生长。肿瘤相关巨噬细胞(TAMs)在ST8Sia6- 在已形成的肿瘤中，表达的肿瘤具有M2样表型，而不是M1样表型 来自缺乏ST8Sia6表达的亲本MC38或B16-F10肿瘤细胞系。我们证明了这一点 ST8Sia6为抑制Siglec的Siglec-E产生配体，Siglec-E的表达仅限于天然免疫 细胞。Siglec-E基因敲除后ST8Sia6表达肿瘤细胞的生长优势消失 小鼠，证明ST8Sia6过表达的主要作用是抑制免疫反应 而不是对细胞生长的内在影响。我们开发了一种新型的依赖于cre的DOX- 可调控的ST8Sia6转基因研究ST8Sia6在自发肿瘤模型中的作用过度表达 ST8Sia6基因在自发性结肠癌模型中的表达显著降低了生存期至2-3个月而不是6个月 几个月，证明了ST8Sia6过表达对体内肿瘤细胞生长的强烈影响。这 该提案将研究ST8Sia6在调节肿瘤免疫反应中的功能。

Checkpoint blockade, which targets inhibitory receptors that suppress successful T cell responses to tumors, demonstrates the critical role that the immune response plays against cancer. However, not all cancers respond to immunotherapy or checkpoint blockade targeting PD-1 or CTLA-4 on T cells. For example, the majority of patients with colon cancer do not respond to checkpoint inhibitor monotherapy, which is effective in only 4% of patients with microsatellite instability. Thus, many tumors may target other inhibitory receptors or different components of the immune system to block it from mounting an effective response. One family of inhibitory receptors on immune cells is the Siglec family, which recognize ligands with sialic acid modifications on cell surface glycoproteins or glycolipids. There are twenty eukaryotic sialic acid transferases, each of which differ in their preferred linkage, targets and number of sialic acids added. It has been long recognized that tumors alter the type and frequency of glycosylation and sialic acid on the cell surface. In particular, increased incorporation of sialic acid is frequently observed in cancer, although the function of hyper-sialylation in promoting and sustaining tumor growth is not well understood. Interestingly, using the COSMIC database, we found that while 389 human tumors over-expressed the sialic acid transferase ST8Sia6, none under-expressed ST8Sia6; this indicates a strong selective advantage for tumors with high ST8Sia6, although the function of ST8Sia6 in cancer is not known. We demonstrated that ST8Sia6 overexpression in either MC38 or B16-F10 tumor cell lines accelerated tumor growth in mice. Tumor associated macrophages (TAMs) in ST8Sia6- expressing tumors possessed an M2-like phenotype, as compared to a M1-like phenotype in tumors formed from the parental MC38 or B16-F10 tumor cell lines that lack ST8Sia6 expression. We demonstrated that ST8Sia6 generates ligands for the inhibitory Siglec, Siglec-E, whose expression is restricted to innate immune cells. The growth advantage of ST8Sia6-expressing tumor cells was lost when injected into Siglec-E knockout mice, demonstrating that the primary effect of ST8Sia6 overexpression is on inhibition of the immune response of the host rather than an intrinsic effect on cell growth. We have developed a novel cre-dependent, dox- regulatable ST8Sia6 transgene to study the effect of ST8Sia6 in spontaneous tumor models. Overexpression of ST8Sia6 in a spontaneous model of colon cancer dramatically decreased survival to 2-3 months instead of 6 months, demonstrating the strong effect ST8Sia6 overexpression has on tumor cell growth in vivo. This proposal will examine the function of ST8Sia6 in modulating the immune response to tumors.