摘要
近年来，嵌合抗原受体T细胞（chimeric antigen receptor T-cell，CAR-T）疗法在血液肿瘤的治疗中取得了突破性进展，但是在实体瘤的治疗中仍然存在着诸多问题，例如CAR-T细胞渗透性差，易发生T细胞耗竭现象、脱靶效应等，故实体瘤的CAR-T疗法需要提出新的治疗策略来提升治疗效果。与单一CAR-T治疗方式相比，CAR-T联合其他肿瘤治疗手段已经在临床前及临床研究中展现出优异疗效。本篇综述总结了CAR-T联用不同肿瘤治疗方法：抗体药物、溶瘤病毒、肿瘤疫苗、纳米药物应对实体瘤治疗的研究进展，以期为开发新的CAR-T联用策略治疗实体瘤提供理论依据和新思路。
CAR-T疗法已在个性化肿瘤治疗中取得突破性进展，并且在血液系统恶性肿瘤的治疗中显示出优异的治疗效果，因此被认为是最有前景的肿瘤治疗方式之一。目前全球已有9款CAR-T细胞治疗产品上市，其中6款靶向CD19，3款靶向BCMA，这些靶点主要针对的适应证有急性白血病、B细胞淋巴瘤、多发性骨髓瘤
血液肿瘤和实体瘤的不同在于血液肿瘤不会形成组织结构，但是实体瘤具有特殊的组织病理学特征，主要表现为：血管组织丰富、血管壁间较宽、结构完整性差、淋巴回流缺失以及大分子药物的选择性外渗和保留，这一现象被称为高通透性和滞留效应（enhanced permeability and retention effect，EPR），是影响CAR-T细胞浸润实体瘤部位的重要原
T细胞的转运则涉及到T细胞和内皮细胞之间的相互作用，在其迁移的过程中，诸多因素如：趋化因子-趋化因子受体不匹配、细胞黏附分子下调以及异常脉管系统的存在都有可能导致肿瘤特异性T细胞归巢失
TME主要由免疫细胞、基质细胞以及其他非细胞成分组成，TME中的成分与肿瘤细胞相互作用从而促进疾病进展以及耐药性的发生，而且这些相互作用使得TME产生乏氧、低pH、免疫抑制性细胞数量增多、抑制受体上调、肿瘤来源细胞因子分泌等现象，这些变化会导致CAR-T治疗效果不
实体瘤治疗效果不佳的部分原因是缺乏高表达的肿瘤特异性抗原（tumor specific antigen，TSA）及肿瘤免疫逃逸机制的发生。TSA仅在肿瘤组织中表达，因此是最理想的靶点，但是其发现、筛选过程较为困难，所以目前大部分的CAR靶点是肿瘤相关抗原（tumor associated antigen，TAA），但是使用TAA可能会影响CAR-T细胞对肿瘤细胞的识别能力，从而导致CAR-T的治疗效果降
抗体药物发挥作用有多种途径，主要包括细胞毒性作用、调节细胞激活能力、 抑制血管内皮生长因子（vascular endothelial growth factors, VEGFs）
目前FDA获批的大部分肿瘤治疗抗体药物需要依赖细胞毒性作用发挥药效。细胞毒性作用主要通过抗体依赖的细胞介导的细胞毒作用（antibody-dependent cell-mediated cytotoxicity，ADCC）、补体依赖性细胞毒性作用（complement-dependent cytotoxicity，CDC）和抗体依赖性细胞吞噬作用（antibody-dependent cell-mediated phagocytosis，ADCP）清除肿瘤细
免疫检查点是一类免疫抑制性的分子，其可以调控T细胞的活化状态，促进免疫耐受发生。常见的免疫检查点主要有PD-1、PD-L1、CTLA-4、LAG-3等，均是实体瘤中广泛分布的免疫检查点，对T细胞的免疫抑制状态有重要作
TME中肿瘤细胞高表达配体蛋白PD-L1、PD-L2，同时T细胞表面PD-1表达上调，使得PD-1/PD-L1通路持续激活，T细胞发生耗竭从而导致药效持续时间短，故PD-1/PD-L1抑制剂可以使得CAR-T细胞恢复活化状
实体瘤的生长和转移需要新生血管，其中有多种生长因子参与肿瘤血管生成，其中最重要的是VEGFs家族。VEGFs通过刺激内皮细胞的增殖、增加血管通透性、在骨髓中募集血管前体细胞来促进肿瘤血管生成，肿瘤内大量无规则的新生血管导致抗肿瘤药物的低效递
溶瘤病毒（oncolytic virus，OV）是一种可以特异性复制，具有嗜瘤性并且保证正常组织不受到破坏的病毒。OV可以通过多种作用机制发挥抗肿瘤作用，即：直接裂解肿瘤、释放TAA、释放细胞内损伤相关分子模式及病原体相关分子模式来激活抗肿瘤免疫应答，或者释放细胞因子及趋化因子来逆转TME中的不利条件起到间接抗肿瘤作
OV联合CAR-T疗法的设计思路有多种，如设计细胞因子分泌型OV、靶向趋化因子受体/配体的OV、负载免疫检查点抑制剂的OV、加装免疫共刺激分子的OV等。设计IL-2、IL-15、TNF-α等细胞因子分泌型OV可以大幅提升CAR-T细胞活
在过去的50年中，治疗性肿瘤疫苗已经进行了大量的临床前及临床研究，其主要通过激活人体免疫系统、发挥特异性抗肿瘤反应来起到治疗作用，是一种很有发展前景的抗肿瘤免疫治疗手段。肿瘤疫苗的作用机制是将抗原递呈给树突状细胞（dendritic cells，DC），再将活化信号传递给T细胞，经过T细胞的活化、增殖和运输后，高效清除肿
细胞疫苗的发展以DC疫苗为主，DC可以通过多种机制摄取TAA及TSA、刺激T淋巴细胞增殖产生抗肿瘤反应。DC细胞的抗原递呈能力、共刺激分子或共抑制分子的表达情况，决定了免疫系统的激活或者抑
核酸疫苗的作用方式是将编码蛋白基因的序列直接导入宿主体内，使其表达抗原蛋白，从而产生免疫反应。联用核酸疫苗和CAR-T疗法可以使淋巴结中的APCs表达CAR-T靶向的目标抗原，从而促进CAR-T细胞在体内大量扩增，解决T细胞耗竭的问题。例如Reinhard
多肽疫苗是通过化学合成技术制备的肿瘤特异性肽，在体内可以激活对多肽疫苗特异性反应的T细胞，从而增强T细胞的扩增能力和持久
纳米药物是指尺寸为1 ~ 1 000 nm的纳米载体或药物，其可以选择性聚集在发病区域并且发挥药效，同时防止药物在正常组织发生聚集现
纳米药物可以促进肿瘤细胞ICD的发生，通过增加免疫效应细胞的浸润、将免疫抑制性TME转化为免疫原性TME来提高抗肿瘤效果。通常化疗、放疗、光热疗法等治疗手段可诱发IC
利用纳米材料的特点，可将需要调控的基因递送到肿瘤细胞或免疫细胞从而改善TME不利环境条件来提升CAR-T细胞治疗效果。目前针对TME设计纳米材料的策略聚焦在包装趋化因子受体、免疫检查点抑制剂、促炎细胞因子、抗炎细胞因子抑制剂等。
纳米材料包装趋化因子受体、免疫检查点抑制剂联合CAR-T治疗可提升T细胞转运、浸润及效应持续性。Miao
解决TSA缺乏问题有两种方式：一种是修饰肿瘤细胞，使其表达更高丰度的抗原，从而招募T细胞发挥作用；另一种是增加APCs和T细胞之间的反应性，提高抗原递呈效果。第一种策略可以促进CAR-T细胞的增殖、提高T细胞在肿瘤组织中的浸润能力。例如Sun
除候选靶抗原缺乏问题外，肿瘤免疫逃逸的发生也需要解决，利用纳米材料可以增加不同靶抗原的识别能力。Alhallak
纳米材料用于增强T细胞增殖能力主要聚焦在增加抗原刺激程度和新型水凝胶的发展
增强抗原刺激的策略是提高靶抗原在全身淋巴系统及肿瘤部位的表达量，从而刺激CAR-T细胞增殖。例如Reinhard
水凝胶可封装CAR-T细胞、细胞因子、免疫检查点抑制剂等，可控制地将细胞释出，并且可以截留细胞因子和免疫检查点抑制剂使得细胞不断受到刺激增殖，同时防止细胞耗竭发生。Grosskopf
靶向外周免疫系统旨在增强次级淋巴器官中的抗原递呈能力和促进CTL的产生，提高外周免疫细胞群的抗肿瘤能
CAR-T疗法虽然已在血液肿瘤的治疗中取得了突破性进展，但在实体瘤的治疗中困难重重，仍有多个问题需要解决，如：TME中的抑制性信号发生、实体瘤抗原靶点匮乏、肿瘤免疫逃逸现象、T细胞浸润效果差、易发生脱靶现象
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