Development of dipeptidyl peptidase inhibitors as novel immune adjuvants

我们已经在多个模型中证实，在肿瘤注射后早期开始抑制DPPs可以防止肿瘤的发展。有趣的是，这种回归发生在肿瘤生长的初始阶段，即使在肿瘤大小达到峰值时DPP抑制停止，也能观察到。对T细胞的需求和选择性记忆的诱导已经通过消耗实验和肿瘤再挑战建立。此外，我们已经证明DPP抑制剂治疗不会增加肿瘤自然诱导的T细胞的大小，而是加速肿瘤启动过程，导致肿瘤生长早期肿瘤反应性T细胞增加。有趣的是，与未接受DPP抑制剂治疗的荷瘤小鼠的T细胞相比，接受DPP抑制剂治疗的小鼠的T细胞在过继转移到淋巴细胞减少小鼠时介导了更强的抗肿瘤作用。值得注意的是，即使在过继转移后没有使用额外的DPP抑制剂，也可以观察到这种增强的T细胞功能。正在进行的实验正在探索增强T细胞功能的基础。尽管DPP抑制剂治疗增加了产生IL-17的T细胞的数量，一种已知具有强大抗肿瘤活性的群体，但在缺乏IL-17或IL-23p19（来自Giorgio Trinchieri博士）的小鼠中，肿瘤消退保持完整，IL-17或IL-23p19是一种细胞因子，在产生IL-17的TC细胞功能中也很重要。通过选择性消耗抗原呈递细胞，我们已经证明，除了DPP抑制剂介导的肿瘤消退需要T细胞外，树突状细胞也是必需的。与肿瘤加速T细胞启动一致，DPP抑制剂治疗导致dc加速运输到肿瘤引流淋巴结。在缺乏DC转运至肿瘤引流淋巴结、CCL19和CCL21的趋化因子的plt/plt小鼠中，抗肿瘤活性丧失。此外，初步数据显示暴露于DPP抑制剂的淋巴结分泌CCL19增加。正在进行的研究正在用缺乏CCL19/21受体的小鼠来证实这些结果。最后，尽管在肿瘤攻击后开始DPP抑制剂治疗并不能阻止肿瘤生长，但在多种肿瘤模型中，DPP抑制剂与肿瘤靶向DC疫苗联合使用可使已建立的大肿瘤消退，包括儿童肉瘤模型。因此，我们的研究表明，DPP抑制剂是一种有效的疫苗佐剂，具有针对dc的新型作用机制，并且可以预测与直接靶向肿瘤特异性T细胞（如细胞因子）的药物协同作用。与Bill Bachovchin博士合作，我们现在正在肿瘤疫苗模型中测试多种选择性靶向不同DPP酶的DPP抑制剂。我们已经确定了第二代化合物，改善了小鼠的治疗窗口，增加了佐剂活性。我们已经开始与成人恶性肿瘤免疫学和生物学实验室的Jeff Schlom博士、James Gulley博士和Jim Hodge博士讨论这种药物的早期临床开发计划。根据这些研究的结果，儿科肿瘤科将考虑使用已经在人体中进行测试的疫苗平台进行后续试验（与Crystal Mackall博士合作的实体瘤疫苗和通过血液和骨髓移植科的血液恶性肿瘤疫苗（见ZIA BC 011295项目）并与Alan Wayne博士合作）。

We have established that inhibition of DPPs prevent tumor development when initiated early after tumor injection in multiple models. Interestingly, this regression occurs after an initial period of tumor growth and is observed even when DPP inhibition is stopped at peak tumor size. The requirement for T cells and the induction of selective memory has been established using depletion experiments and tumor rechallenge. In addition, we have demonstrated that DPP inhibitor treatment does not increase the magnitude of the T cells naturally induced by tumors, but rather accelerates the process of tumor priming resulting in increased tumor-reactive T cells early during tumor growth. Interestingly, T cells from tumor-bearing DPP inhibitor treated mice mediate superior anti-tumor effects upon adoptive transfer into lymphopenic mice when compared to T cells from tumor bearing mice not receiving DPP inhibitor. Remarkably, this enhanced T cell functionality is observed even when no additional DPP inhibitor is administered following adoptive transfer. Ongoing experiments are exploring the basis for enhanced T cell function. Although DPP inhibitor treatment increases the number of IL-17-producing T cells, a population known to posses potent anti-tumor activity, tumor regression remained intact in mice lack IL-17 or IL-23p19 (obtained from Dr. Giorgio Trinchieri), a cytokine also important in IL-17 producing TC ell function. Using selective depletion of antigen presenting cells we have demonstrated that, in addition to the T cell requirement for DPP inhibitor-mediated tumor regression, dendritic cells are also required. Consistent with the accelerated T cell priming by tumor, DPP inhibitor treatment results in accelerated trafficking of DCs to tumor draining lymph nodes. Anti-tumor activity is lost in plt/plt mice lacking the chemokines responsible DC trafficking to tumor draining lymph node, CCL19 and CCL21. In addition, preliminary data demonstrates increased secretion of CCL19 by lymph nodes exposed to DPP inhibitors. Ongoing studies are confirming these results using mice deficient in the receptor for CCL19/21 on DCs, CCR7. Finally, although initiation of DPP inhibitor treatment later following tumor challenge does not prevent tumor growth, combination of DPP inhibitor with tumor-targeted DC vaccination results in regression of large established tumors in multiple tumor models including a model of pediatric sarcoma. Thus, our studies demonstrate that DPP inhibitors represent potent vaccine adjuvants with novel mechanism of action that targets DCs and would be predicted act synergistically with agents directly targeting tumor-specific T cells such as cytokines. In collaboration with Dr. Bill Bachovchin, we are now testing multiple DPP inhibitors with selective targeting of different DPP enzymes in our tumor vaccine models. We have identified a second-generation compound with improved therapeutic window in mice and increased adjuvant activity. We have begun to discuss a early phase clinical development plan for this agent with Dr. Jeff Schlom, Dr. James Gulley and Dr. Jim Hodge in the Laboratory of Tumor Immunology and Biology in adult malignancies. Depending on the outcome of these studies, subsequent trials will be considered in the Pediatric Oncology Branch using vaccine platforms already being tested in humans (solid tumor vaccines in collaboration with Dr. Crystal Mackall and hematologic malignancies through the Blood and Marrow Transplant Section (see Project ZIA BC 011295) and in collaboration with Dr. Alan Wayne).