展示靶向单链抗体(scFv)的细菌膜影(ghost)递送线性DNA疫苗的分子机制研究

There is an urgent need to establish the efficient and low cost method to produce DNA vaccine worldwide. We have tried to developed the large-scale PCR (>1000ml) technique to obtain low-cost linear DNA vaccine ; however, its intrinsic high vaccination dose (>100 ug each time) due to the inefficient uptake limits its application. Considering the great advantages of recent developed adjuvant – empty bacterial (ghost) and the targeting scFv, we postulated that the efficient combination of ghost and scFv may overcome this limitation. To achieve this goal, we have successfully developed a super folding fluorescent protein vector that can highly express fusion scFv in the bacterial out membrane and prepared ghost that is capable of carrying a linear DNA to immune cells in vitro. Based on this work, we plan to further optimize the super folding fluorescent protein expression system to express targeting scFv in the bacterial out membrane to improve the ability of ghost to load more linear DNA. Our purpose is to establish a comprehensive vaccination model that can deliver both inner and outer vector can load immune stimulating substance, such as linear DNA vaccine is loaded in the ghost target scFv is attached to out membrane of ghost. Elucidating the mechanism of comprehensive vaccination method will provide important insights for development of high efficient, safe and DNA vaccine as well as establishement of prevention models in response to the emerging infectious diseases.

随着DNA疫苗国内外的相继上市，探讨高效、低成本生产模式的研究备受青睐。课题组建立的高效、安全的大规模PCR(>1000ml/次)获得线性DNA疫苗的方法应势而生，但其低效被摄取而导致的高接种剂量(>100μg/次)限制了其应用。借助免疫佐剂-细菌膜影(ghost)和靶向单链抗体(scFv)的研究结果，我们推测构建具有二者的优点靶向性递送载体或许可突破这一限制。课题组前期构建了高效表达融合的scFv于细菌外膜的超折叠荧光蛋白(sfGFP)表达载体，证实了利用裂解质粒制备的ghost在体外具有携带线性DNA至免疫细胞的能力。鉴于此，本研究拟进一步验证sfGFP表达体系融合表达靶向scFv的可能性及以此制备的ghost荷载线性DNA能力，建立一种靶向性疫苗模式。充分阐明靶向疫苗制备的分子机制，可为深入探讨制备高效、安全DNA疫苗而快速应对新发传染病的预防模式提供重要的参考。

鉴于病毒性疾病流行对人类健康威胁的严重不断增加和DNA疫苗的优势，研究者越来越关注DNA疫苗的高效、低成本生产模式。课题组建立的高效、安全的大规模PCR获得线性DNA疫苗的方法应势而生，但其在体内的低被摄率而导致的高接种剂量限制了其应用。随着对细菌膜影（BGs）和靶向单链抗体（scFv）的深入研究，我们推测构建具有二者的优点靶向性递送载体或许可突破大规模PCR制备线性DNA疫苗的应用限制。课题组首先优化了大规模PCR制备线性DNA疫苗的方法，然后我们设计了针对小鼠树突状细胞表面受体分子DEC-205的单链抗体scNLDC融合sfGFP表达的重组质粒pET23a-sfGFP-scNLDC，重组质粒成功在大肠杆菌获得可溶性表达，并且表达纯化的单链抗体scNLDC与DC 2.4细胞具有较强亲和性。在此基础上，将表达scNLDC的质粒（pET23a-sfGFP-scNLDC）与制备细菌膜影的裂解质粒（pBV220-E）共同转化至大肠杆菌Rosetta Blue中，通过IPTG和42 ℃升温诱导制备了展示靶向单链抗体scNLDC的细菌膜影 （scBGs），用于线性DNA疫苗的递送载体。与单独的线性DNA疫苗或传统细菌膜影递送线性DNA疫苗相比，展示靶向单链抗体scNLDC的ghost递送线性DNA疫苗免疫BALB/c小鼠可诱导更强的特异性免疫应答和保护效率。我们建立的以展示靶向scFv的scBGs作为线性DNA疫苗递送载体的模式，可为深入探讨制备高效、安全DNA疫苗而快速应对新发传染病的预防模式提供重要的参考。