经CD19分子将抗原HER2和CD137靶向至B细胞以增强抗乳腺癌免疫应答机制的研究

Immunotherapy has become the latest clinical therapeutic intervention in breast cancer treatment. In our previous studies, we have designed the B cell vaccine (scFv-HER2) and demonstrated that targeting tumor-associated Ag HER2 to B cells via anti-CD19 single chain variable fragment (scFv) could elicit anti-tumor immune response to inhibit the growth of breast cancer cells, however, tumor was not eradicated by immune system which indicated that there are still some tumor cells evading from immune surveillance. A mechnism of tumor escape from immune surveillance is to promote activation-induced cell death (AICD) of effector T cells, so to reduce activation-induced cell death (AICD) of effector T cells will inhibit the immune escape of tumor cells. The CD137 is expressed by activated T cells, studies have shown that agonistic anti-CD137 monoclonal antibody can reduce activation-induced cell death (AICD) of effector T cells and enhance the cytotoxic activity of T cells. Based on our previous study, we plan to conjugate CD137 to get new vaccine scFv-CD137-HER2, which will target two antigens (HER2 and CD137) to B cells via CD19. Hopefully, this new strategy can elicit more effective anti-tumor antibody and enhance antigen specific T cells response, lower the activation-induced cell death of T cells, prolong the life of effector T cells and further promote the cytotoxic activity of T cells. Finally, we want to achieve the long-term anti-tumor effect and provide new ideas for the clinical treatment of breast cancer.

免疫治疗已成为乳腺癌治疗的新手段。我们前期设计的B细胞疫苗（scFv-HER2）通过CD19分子单链抗体（scFv）将肿瘤抗原HER2靶向至B细胞，可增强抗肿瘤免疫应答，明显抑制乳腺癌细胞生长，但肿瘤并未根除，提示仍有部分肿瘤细胞逃逸免疫监视,而促进T细胞活化诱导细胞死亡（AICD）是肿瘤逃逸免疫监视的其中一个重要机制， 因此在前期研究基础上抑制T细胞AICD则有助于抑制肿瘤免疫逃逸。CD137分子主要表达在活化T细胞等细胞表面，其活化型抗体可降低T细胞AICD,增强T细胞杀伤效应。故项目在前期基础上偶联CD137得到新的疫苗scFv-CD137-HER2，将抗原HER2和CD137同时靶向至B细胞，期望产生抗肿瘤抗体，增强抗原特异性T细胞应答，同时通过产生的CD137抗体减少T细胞AICD，维持效应性T细胞寿命，进一步增强T细胞杀伤功能，达到长效抗肿瘤效果，为乳腺癌的临床治疗提供新思路。

近几年，肿瘤的免疫治疗取的重要进展，然而仍有多种类型肿瘤能够逃逸免疫监视，其原因在于机体对肿瘤抗原的耐受。本课题通过制备CD19抗体的单链抗体scFv，然后偶联肿瘤抗原Her2D4，靶向B细胞，发现scFv-her2D4靶向B细胞后，能够打破宿主对肿瘤抗原的耐受能有效的产生抗肿瘤抗体，同时B细胞作为抗原提呈细胞也能够有效的活化T细胞，增强宿主的抗肿瘤免疫应答能力。同时我们深入分析了scFv-her2D4对肿瘤微环境中免疫细胞的影响，发现融合蛋白能够增加肿瘤组织中免疫细胞的浸润，活化肿瘤微环境中免疫细胞，改善肿瘤微环境，抑制肿瘤生长。同时我们也检测了融合蛋白与PD1抗体联合治疗乳腺癌和结肠癌的效果和抗肿瘤应答机制，发现联合治疗优于单个治疗，联合治疗能够明显抑制肿瘤生长，甚至缩小肿瘤体积使肿瘤消失。本项目研究为肿瘤的免疫治疗开辟一个新的方向，为后续肿瘤免疫治疗奠定基础。

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