Nonfucosylation of an anti-TIGIT antibody enhances FcyR engagement, driving innate immune activation and antitumor activity

TIGIT is an immune checkpoint receptor expressed on activated and memory T cells, immunosuppressive T regulatory cells, and natural killer (NK) cells. TIGIT has emerged as an attractive target for antitumor therapies, due to its proposed immunosuppressive effects on lymphocyte function and T cell activation. We generated an anti-TIGIT monoclonal antibody (mAb) that binds with high affinity to human, non-human primate, and murine TIGIT and through multiple experimental methodologies demonstrated that checkpoint blockade alone is insufficient for antitumor activity. Generating anti-TIGIT mAbs with various Fc backbones we show that muting the Fc-Fcγ receptor (FcγR) interaction failed to drive antitumor activity, while mAbs with Fc functional backbones demonstrate substantial antitumor activity, mediated through activation of antigen-presenting cells (APCs), T cell priming, and NK-mediated depletion of suppressive Tregs and exhausted T cells. Further, nonfucosylation of the Fc backbone resulted in enhanced immune responses and antitumor activity relative to the intact IgG1 backbone. The improved activity correlated with the biased FcγR interaction profile of the nonfucosylated anti-TIGIT mAb, which supports that FcγRIIIa binding with decreased FcγRIIb binding favorably activates APCs and enhances tumor-specific CD8+ T cell responses. The anti-TIGIT mAbs with intact FcγR interacting backbones also demonstrated synergistic enhancement of other standard antitumor treatments, including anti-PD-1 treatment and a model monomethyl auristatin E antibody–drug conjugate. These findings highlight the importance of the anti-TIGIT mAb’s Fc backbone to its antitumor activity and the extent to which this activity can be enhanced through nonfucosylation of the backbone Bulk RNA-seq was performed on tumors from syngeneic mouse models, and gene-level transcript levels were subsequently used to compute immune-related gene signature scores that were correlated with the activity of SEA-TGT in those models.

TIGIT是一类免疫检查点受体（immune checkpoint receptor），可在活化T细胞、记忆性T细胞、免疫抑制性调节性T细胞以及自然杀伤（natural killer, NK）细胞表面表达。鉴于其对淋巴细胞功能与T细胞活化的潜在免疫抑制作用，TIGIT已成为抗肿瘤治疗的极具吸引力的靶点。本研究构建了一株可与人、非人灵长类及小鼠TIGIT高亲和力结合的抗TIGIT单克隆抗体（anti-TIGIT monoclonal antibody, mAb），并通过多种实验方法证实，仅依靠检查点阻断无法实现抗肿瘤活性。通过构建携带不同Fc骨架（Fc backbone）的抗TIGIT mAb，本研究发现，阻断Fc-Fcγ受体（Fcγ receptor, FcγR）相互作用无法介导抗肿瘤活性；而携带功能性Fc骨架的mAb则可展现出显著的抗肿瘤活性，其作用机制包括激活抗原呈递细胞（antigen-presenting cells, APCs）、启动T细胞应答，以及通过NK细胞介导清除免疫抑制性调节性T细胞（Tregs）与耗竭性T细胞。进一步研究显示，与完整IgG1骨架相比，Fc骨架的非岩藻糖基化（nonfucosylation）修饰可增强免疫应答与抗肿瘤活性。这种活性提升与非岩藻糖基化抗TIGIT mAb偏向性的FcγR相互作用特征相关，该特征表明，FcγRIIIa结合能力增强且FcγRIIb结合能力减弱的模式，可有效激活APCs并增强肿瘤特异性CD8+ T细胞应答。携带完整FcγR相互作用骨架的抗TIGIT mAb，还可与其他标准抗肿瘤治疗手段产生协同增效作用，包括抗PD-1治疗以及一款基于单甲基澳瑞他汀E（monomethyl auristatin E）的抗体药物偶联物模型。上述研究结果凸显了抗TIGIT mAb的Fc骨架对其抗肿瘤活性的重要性，以及通过Fc骨架非岩藻糖基化修饰可实现的活性提升幅度。本研究对同基因小鼠模型的肿瘤组织进行了批量RNA测序（bulk RNA-seq），随后基于基因水平的转录本水平计算免疫相关基因特征评分，并将其与这些模型中SEA-TGT的活性进行关联分析。