放疗可以通过诱导肿瘤的免疫原性细胞死亡和急性炎症来产生疫苗效应和重塑肿瘤微环境，促进抗肿瘤免疫的发生。然而，由于有限的抗原呈递、免疫抑制微环境和肿瘤内的慢性炎症，单纯放射治疗往往难以引起全身性的抗肿瘤免疫应答。因此，迫切需要开发新的策略来解决这些问题。

肽基纳米材料因具有载药高效，合成简单等优势获得广泛关注。更重要的是，其可以作为有效的抗原递送系统，来提高抗原的稳定性和免疫原性。并且，其可以通过酶响应的方式，在生物体内形成聚集和组装，实现更好的生物分布和组织滞留。

基于以上背景，我们构建了酶响应的原位多肽纳米纤维疫苗，来增强放射免疫联合治疗的效果。我们将环氧合酶-2抑制剂氟比洛芬（Fbp）共价连接在多肽组装模块G^DF^DF^DpY上。Fbp-G^DF^DF^DpY能够在高表达碱性磷酸酶（ALP）的4T1细胞表面发生响应性组装，并捕获放疗诱导肿瘤细胞释放的细胞外囊泡和自体抗原，形成纳米纤维疫苗。该疫苗可以作为“抗原库”持续缓慢的释放抗原；同时，多肽纳米纤维的佐剂效应能够促进DC细胞对抗原的摄取和交叉提呈，激活抗肿瘤免疫。此外，纳米疫苗对环氧合酶表达的抑制能够促进M2-巨噬细胞向M1表型的重极化，减少调节性T细胞和髓源性抑制细胞的数量，以实现抑制性免疫微环境的重塑。动物实验表明，纳米疫苗与放射治疗联用对4T1肿瘤的抑制率可以达到76%，并表现出良好的生物相容性。

综上所述，我们提出了一种新型的原位酶促多肽纳米疫苗，不仅可以放大放射治疗的原位疫苗效应，还能够重塑照射后的抑制性肿瘤免疫微环境，提高肿瘤放射免疫联合治疗效果。

Radiotherapy can generate a vaccine effect and reshape the tumor microenvironment by inducing immunogenic cell death and acute inflammation in tumors, thereby promoting the occurrence of anti-tumor immunity. However, due to limited antigen presentation, an immunosuppressive microenvironment, and chronic inflammation within the tumor, simple radiotherapy often fails to elicit a systemic anti-tumor immune response. Therefore, there is an urgent need to develop new strategies to address these issues.

Peptide-based nanomaterials have attracted widespread attention due to their advantages of efficient drug loading, simple synthesis, and more importantly, their ability to serve as effective antigen delivery systems to enhance the stability and immunogenicity of antigens. Additionally, they can form aggregates and assemble in vivo through enzyme responsiveness, achieving better biodistribution and tissue retention.

Against this background, we constructed an enzyme-responsive in situ polypeptide nanofiber vaccine to enhance the effects of radioimmune combination therapy. We covalently linked the COX-2 inhibitor Flurbiprofen (Fbp) to the multipeptide G^DF^DF^DpY. Fbp-G^DF^DF^DpY could undergo responsive assembly on the surface of 4T1 cells overexpressing alkaline phosphatase (ALP) and capture small extracellular vesicles and autologous antigens released by radiotherapy-induced tumor cells, forming a nanofiber vaccine. This vaccine acts as a ‘library’ of antigens that releases antigens slowly and continuously; meanwhile, the adjuvant effect of the peptide nanofibers can promote the uptake and cross-presentation of antigens by DC cells, activating anti-tumor immunity. Furthermore, the suppression of cyclooxygenase expression by the nanovaccine can promote the polarization of M2 macrophages towards the M1 phenotype, reduce the number of regulatory T cells and myeloid-derived suppressor cells, and thus reshape the immunosuppressive tumor microenvironment. Animal experiments showed that the combined use of the nanovaccine and radiotherapy could achieve a tumor suppression rate of 76% for 4T1 tumors and demonstrated good biocompatibility.

In summary, we proposed a novel in situ enzyme-instructed peptide nanovaccine, which can not only amplify the in situ vaccine effect of radiation therapy, but also reshape the inhibitory tumor immune microenvironment after irradiation, and improve the efficacy of tumor combined radioimmunotherapy.