Department of Translational Medicine, MedImmune, One Medimmune Way, Gaithersburg, MD 20878 USA.
Department of Infectious Disease and Vaccines, MedImmune, One Medimmune Way, Gaithersburg, MD 20878 USA.
J Immunother Cancer. 2017 Jun 20;5:47. doi: 10.1186/s40425-017-0247-0. eCollection 2017.
The expansion of antigen-specific CD8 T cells is important in generating an effective and long-lasting immune response to tumors and viruses. Glucocorticoid-induced tumor necrosis factor receptor family-related receptor (GITR) is a co-stimulatory receptor that binds the GITR ligand (GITRL). Agonism of GITR can produce important signals that drive expansion of effector T cell populations.
We explored two separate murine tumor models, CT26 and TC-1, for responsiveness to GITR Ligand Fusion Protein(GITRL-FP) monotherapy. In TC-1, GITRL-FP was also combined with concurrent administration of an E7-SLP vaccine. We evaluated tumor growth inhibition by tumor volume measurements as well as changes in CD8 T cell populations and function including cytokine production using flow cytometry. Additionally, we interrogated how these therapies resulted in tumor antigen-specific responses using MHC-I dextramer staining and antigen-specific restimulations.
In this study, we demonstrate that a GITR ligand fusion protein (GITRL-FP) is an effective modulator of antigen-specific CD8 T cells. In a CT26 mouse tumor model, GITRL-FP promoted expansion of antigen-specific T cells, depletion of regulatory T cells (Tregs), and generation of long-lasting CD8 T cell memory. This memory expansion was dependent on the dose of GITRL-FP and resulted in complete tumor clearance and protection from tumor rechallenge. In contrast, in TC-1 tumor-bearing mice, GITRL-FP monotherapy could not prime an antigen-specific CD8 T cell response and was unable to deplete Tregs. However, when combined with a vaccine targeting E7, treatment with GITRL-FP resulted in an augmentation of the vaccine-induced antigen-specific CD8 T cells, the depletion of Tregs, and a potent antitumor immune response. In both model systems, GITR levels on antigen-specific CD8 T cells were higher than on all other CD8 T cells, and GITRL-FP interacted directly with primed antigen-specific CD8 T cells.
When taken together, our results demonstrate that the delivery of GITRL-FP as a therapeutic can promote anti-tumor responses in the presence of tumor-specific CD8 T cells. These findings support further study into combination partners for GITRL-FP that may augment CD8 T-cell priming as well as provide hypotheses that can be tested in human clinical trials exploring GITR agonists including GITRL-FP.
抗原特异性 CD8 T 细胞的扩增对于产生针对肿瘤和病毒的有效和持久免疫反应非常重要。糖皮质激素诱导的肿瘤坏死因子受体家族相关受体（GITR）是一种共刺激受体，它与 GITR 配体（GITRL）结合。GITR 的激动作用可以产生重要的信号，驱动效应 T 细胞群体的扩增。
我们探索了两种独立的小鼠肿瘤模型，CT26 和 TC-1，以研究它们对 GITR 配体融合蛋白（GITRL-FP）单药治疗的反应。在 TC-1 中，GITRL-FP 还与同时给予 E7-SLP 疫苗联合使用。我们通过肿瘤体积测量评估肿瘤生长抑制情况，以及通过流式细胞术评估 CD8 T 细胞群体和功能的变化，包括细胞因子产生。此外，我们使用 MHC-I 二聚体染色和抗原特异性再刺激来探究这些治疗方法如何导致肿瘤抗原特异性反应。
在这项研究中，我们证明了 GITR 配体融合蛋白（GITRL-FP）是一种有效的抗原特异性 CD8 T 细胞调节剂。在 CT26 小鼠肿瘤模型中，GITRL-FP 促进了抗原特异性 T 细胞的扩增、调节性 T 细胞（Tregs）的耗竭和长效 CD8 T 细胞记忆的产生。这种记忆的扩增依赖于 GITRL-FP 的剂量，并导致完全清除肿瘤和防止肿瘤再挑战。相比之下，在 TC-1 荷瘤小鼠中，GITRL-FP 单药治疗不能引发抗原特异性 CD8 T 细胞反应，也不能耗竭 Tregs。然而，当与靶向 E7 的疫苗联合使用时，GITRL-FP 治疗导致疫苗诱导的抗原特异性 CD8 T 细胞、Tregs 的耗竭和有效的抗肿瘤免疫反应增强。在这两种模型系统中，抗原特异性 CD8 T 细胞上的 GITR 水平高于所有其他 CD8 T 细胞，并且 GITRL-FP 直接与初始抗原特异性 CD8 T 细胞相互作用。
综上所述，我们的结果表明，在存在肿瘤特异性 CD8 T 细胞的情况下，GITRL-FP 的递送可以促进抗肿瘤反应。这些发现支持进一步研究 GITRL-FP 的联合伙伴，这些伙伴可能增强 CD8 T 细胞的初始，以及提供可以在探索 GITR 激动剂（包括 GITRL-FP）的人类临床试验中测试的假设。
