Helen Diller Family Comprehensive Cancer Center, UCSF, San Francisco, CA, USA.
Department of Dermatology, UCSF, San Francisco, CA, USA.
J Immunother Cancer. 2019 Mar 4;7(1):62. doi: 10.1186/s40425-018-0493-9.
Checkpoint blockade immunotherapy has improved metastatic cancer patient survival, but response rates remain low. There is an unmet need to identify mechanisms and tools to circumvent resistance. In human patients, responses to checkpoint blockade therapy correlate with tumor mutation load, and intrinsic resistance associates with pre-treatment signatures of epithelial mesenchymal transition (EMT), immunosuppression, macrophage chemotaxis and TGFβ signaling.
To facilitate studies on mechanisms of squamous cell carcinoma (SCC) evasion of checkpoint blockade immunotherapy, we sought to develop a novel panel of murine syngeneic SCC lines reflecting the heterogeneity of human cancer and its responses to immunotherapy. We characterized six Kras-driven cutaneous SCC lines with a range of mutation loads. Following implantation into syngeneic FVB mice, we examined multiple tumor responses to α-PD-1, α-TGFβ or combinatorial therapy, including tumor growth rate and regression, tumor immune cell composition, acquired tumor immunity, and the role of cytotoxic T cells and Tregs in immunotherapy responses.
We show that α-PD-1 therapy is ineffective in establishing complete regression (CR) of tumors in all six SCC lines, but causes partial tumor growth inhibition of two lines with the highest mutations loads, CCK168 and CCK169. α-TGFβ monotherapy results in 20% CR and 10% CR of established CCK168 and CCK169 tumors respectively, together with acquisition of long-term anti-tumor immunity. α-PD-1 synergizes with α-TGFβ, increasing CR rates to 60% (CCK168) and 20% (CCK169). α-PD-1 therapy enhances CD4 + Treg/CD4 + Th ratios and increases tumor cell pSmad3 expression in CCK168 SCCs, whereas α-TGFβ antibody administration attenuates these effects. We show that α-TGFβ acts in part through suppressing immunosuppressive Tregs induced by α-PD-1, that limit the anti-tumor activity of α-PD-1 monotherapy. Additionally, in vitro and in vivo, α-TGFβ acts directly on the tumor cell to attenuate EMT, to activate a program of gene expression that stimulates immuno-surveillance, including up regulation of genes encoding the tumor cell antigen presentation machinery.
We show that α-PD-1 not only initiates a tumor rejection program, but can induce a competing TGFβ-driven immuno-suppressive program. We identify new opportunities for α-PD-1/α-TGFβ combinatorial treatment of SCCs especially those with a high mutation load, high CD4+ T cell content and pSmad3 signaling. Our data form the basis for clinical trial of α-TGFβ/α-PD-1 combination therapy (NCT02947165).
检查点阻断免疫疗法提高了转移性癌症患者的生存率，但反应率仍然很低。因此需要寻找识别机制和工具来规避耐药性。在人类患者中，对检查点阻断治疗的反应与肿瘤突变负荷有关，而内在的耐药性与上皮间质转化（EMT）、免疫抑制、巨噬细胞趋化和 TGFβ信号的预处理特征相关。
为了促进对鳞状细胞癌（SCC）逃避检查点阻断免疫治疗机制的研究，我们试图开发一种新的小鼠同源 SCC 系面板，反映人类癌症的异质性及其对免疫治疗的反应。我们对六种 Kras 驱动的皮肤 SCC 系进行了特征分析，这些系具有不同的突变负荷。将这些系植入同基因 FVB 小鼠后，我们观察了多种肿瘤对 α-PD-1、α-TGFβ 或联合治疗的反应，包括肿瘤生长速度和消退、肿瘤免疫细胞组成、获得的肿瘤免疫以及细胞毒性 T 细胞和 Tregs 在免疫治疗反应中的作用。
我们发现，α-PD-1 治疗对所有六种 SCC 系均不能有效地建立完全消退（CR），但对突变负荷最高的两个系 CCK168 和 CCK169 的肿瘤生长有部分抑制作用。α-TGFβ 单药治疗可使已建立的 CCK168 和 CCK169 肿瘤分别有 20%和 10%的 CR，同时获得长期抗肿瘤免疫。α-PD-1 与 α-TGFβ 协同作用，使 CR 率提高到 60%（CCK168）和 20%（CCK169）。α-PD-1 治疗可增加 CCK168 SCC 中的 CD4+Treg/CD4+Th 比值，并增加肿瘤细胞 pSmad3 的表达，而 α-TGFβ 抗体治疗可减弱这些作用。我们表明，α-TGFβ 部分通过抑制由 α-PD-1 诱导的抑制性 Tregs 发挥作用，这些 Tregs 限制了 α-PD-1 单药治疗的抗肿瘤活性。此外，在体外和体内，α-TGFβ 直接作用于肿瘤细胞，减弱 EMT，激活免疫监视的基因表达程序，包括上调肿瘤细胞抗原呈递机制的基因表达。
我们表明，α-PD-1 不仅启动了肿瘤排斥程序，还可以诱导竞争性 TGFβ 驱动的免疫抑制程序。我们为 α-PD-1/α-TGFβ 联合治疗 SCC 提供了新的机会，特别是对于突变负荷高、CD4+T 细胞含量高和 pSmad3 信号高的 SCC。我们的数据为 α-TGFβ/α-PD-1 联合治疗的临床试验（NCT02947165）奠定了基础。
