Self-associated molecular patterns mediate cancer immune evasion by engagement of Siglec receptors

Cancer immunotherapy targeting inhibitory receptors on T cells has changed the landscape of oncological practice, but most patients do not respond to current approaches. Thus, new targets on T cells for cancer immunotherapy are needed. CD33-related Siglecs are pattern recognition immune receptors binding to a broad range of sialoglycan ligands, which appear to function as self-associated molecular patterns (SAMPs) to dampen unwanted immune responses against self. Naïve T cells in humans have very low levels of inhibitory Siglec expression. Here, we show Siglec-9 in non-small cell lung cancer (NSCLC) are significantly upregulated on tumor-infiltrating T cells. These findings were confirmed in other tumor types including colorectal cancer, and ovarian cancer. Characterization of Siglec-9 expressing T cells showed a co-expression of inhibitory receptors including PD-1 and a distinct phenotype with increased cytokine production upon restimulation, compared to Siglec negative T cells. Functional analysis by reduction of sialoglycan-SAMPs on tumor cells in vitro and in vivo demonstrated an increased tumor cell killing and an inhibition of tumor growth. Overexpression of inhibitory Siglecs on T cells enhanced tumor growth in mice and exchange of inhibitory Siglecs on mouse T cells with an activating Siglec enhanced anti-cancer immunity. Increased T cell expression of Siglec-9 in NSCLC patients also correlated with survival, and analysis of Siglec-9 polymorphisms showed an association with the risk of developing lung and colorectal cancer. Our data identify the sialoglycan-SAMP/Siglec pathway as potential new target to improve T cell activation and cancer immunotherapy. Six non-small cell lung cancer tumor infiltrating CD8+ T cells (CD45+ CD3+ CD8+ CD4-) were sorted by flow cytometry according to their Siglec9 staining into Siglec9+ and Siglec9- samples.

靶向T细胞表面抑制性受体的癌症免疫治疗已重塑了肿瘤临床实践的格局，但多数患者无法对现有治疗方案产生应答。因此，开发靶向T细胞的新型癌症免疫治疗靶点迫在眉睫。CD33相关唾液酸结合免疫球蛋白样凝集素（CD33-related Siglecs）是一类可结合多种唾液酸聚糖配体的模式识别免疫受体，这类配体可作为自身相关分子模式（SAMPs），抑制针对自身组织的不必要免疫应答。人类初始T细胞的抑制性Siglec表达水平极低。本研究发现，非小细胞肺癌（NSCLC）患者的肿瘤浸润T细胞中Siglec-9的表达显著上调。这一发现在结直肠癌、卵巢癌等其他肿瘤类型中得到了验证。对表达Siglec-9的T细胞进行表征后发现，与Siglec阴性T细胞相比，这类细胞共表达包括程序性死亡受体1（PD-1）在内的多种抑制性受体，且在再刺激后可产生更多细胞因子，具备独特的表型特征。通过体外及体内实验降低肿瘤细胞表面的唾液酸聚糖-SAMPs水平的功能分析表明，该操作可增强肿瘤细胞杀伤效果并抑制肿瘤生长。在小鼠T细胞中过表达抑制性Siglecs可促进肿瘤生长，而将小鼠T细胞表面的抑制性Siglecs替换为激活性Siglecs则可增强抗肿瘤免疫。非小细胞肺癌患者体内Siglec-9在T细胞的高表达还与患者生存期相关；对Siglec-9多态性的分析显示，其与肺癌及结直肠癌的发病风险存在关联。本研究证实，唾液酸聚糖-SAMP/Siglec通路可作为改善T细胞活化及癌症免疫治疗的潜在新型靶点。本研究选取6例非小细胞肺癌患者的肿瘤浸润CD8+ T细胞（CD45+ CD3+ CD8+ CD4-），通过流式细胞术根据Siglec9染色情况将其分选为Siglec9阳性及Siglec9阴性样本。