为实现免疫和化疗联合治疗转移性肿瘤，提高载药纳米粒的稳定性和药物定点可控释放，本项目拟构建一类具有ATP与肿瘤微环境pHe（pH6.2-6.9）双重敏感，集免疫检查点抑制剂与化疗药物于一体的新型DNA纳米凝胶载药系统。合成单链DNA接枝聚乙二醇-聚天冬氨酸-聚苯丙氨酸三嵌段聚合物为载体，部分主链通过pHe敏感键偶联PD-L1多肽抑制剂DPPA-1，其余主链偶联细胞穿透肽R8。双亲性主链自组装形成纳米胶束；ATP适配体与聚合物上DNA通过碱基互补配对作用形成高度结构化的网络，同时利用DNA负载阿霉素，获得高稳定性的载药DNA纳米凝胶。利用DPPA-1识别肿瘤细胞表面的PD-L1，pHe触发酰胺键断裂释放DPPA-1，阻断PD-1/PD-L1信号通路，逆转免疫抑制反应；R8协助纳米凝胶穿膜入胞，胞内高浓度ATP使DNA双链解聚释放阿霉素，杀死肿瘤细胞，激活人体抗肿瘤免疫反应，从而增强疗效。

In order to achieve the combination of immunotherapy and chemotherapy in the treatment of metastatic tumor, improve nanoparticles’ stability and control drug release, we construct a nogvel ATP and tumor microenvironment pHe (pH6.2-6.9)responsive DNA nanogel drug delivery system loading immune checkpoint blockers and chemotherapeutic drugs. Single chain DNA grafted poly(ethylene glycol)-poly(aspartic acid)-poly(phenylalanine) three block polymers is synthesized as the carrier materials. DPPA-1, a PD-L1 inhibitor, is conjugated on a part of the copolymer through the pHe sensitive bond and cell penetrating peptide R8 is immobilized on the other part of the copolymer. First, the copolymer self-assembled micelles via the hydrophobic force. Next, ATP aptamers crosslink to complementary DNA through base pairing interaction to form a highly structured network, meanwhile doxorubicin is intercalated into double stranded DNA. The drug-loaded DNA nanogel is fabricated. The DPPA-1 in the nanogel identify PD-L1 on the surface of the tumor cells and the weak acidic environment in tumor cleave the amide bond in the nanogel to release DPPA-1. DPPA-1 can block the PD-1/PD-L1 signaling pathway, resulting in the reverse of immunosuppression and the induction of immune surveillance. Subsequently, R8 facilitates nanogel to enter cells. Abundant ATP in cytosol can trigger the duplex-to-aptamer change, leading to the accelerated release of DOX. DOX can kill tumor cells and elicit anticancer immune responses of human body. The combination of immunotherapy and chemotherapy is expected to achieve efficiency in the treatment of advanced tumor.