腺病毒载体在疫苗研发和基因治疗领域应用广泛，但常用腺病毒载体均基于现存野生毒株改造而来，临床应用时受到人群既有免疫的限制。本项目的科学假设是：现存病毒的共同祖先毒株具有更加广泛的组织嗜性，不受人群现存免疫水平影响，可能成为新型的腺病毒载体。本项目拟通过分析人等宿主的腺病毒表面蛋白序列，基于进化树和贝叶斯整合模型推断种、属和型共3个层次的共同祖先序列。采用同源建模方法构建祖先序列对应的表面蛋白三维结构模型，用分子动力学模拟检验祖先蛋白核衣壳结构的稳定性。人工合成腺病毒祖先毒株表面蛋白对应的核酸序列编码区，替换现有腺病毒载体基因组的相应片段，构建复制缺陷型载体，在细胞和动物水平验证该祖先序列重建载体的组织嗜性和免疫原性。复制缺陷型载体不能感染健康的动物或者人，具有良好的生物安全性。该项目有助于深入理解腺病毒分子进化历史，探索病毒的组织嗜性等致病机制，还能够开发新型腺病毒载体。

Adenovirus vectors are widely used in vaccine development and gene therapy, but adenoviral vectors in current usage have been derived from circulating wild strains whose clinical application are limited by the immunity existing in modern human population. The scientific hypothesis of this project is that there is a co-evolution network among the human adenovirus surface proteins, then the common ancestral strain of the current viruses has a more extensive tropism for tissue, which is not affected by the population's existing immunity level. This ancestral stain may serve as a novel type of adenovirus vector. This project aims to infer the common ancestral sequences based on phylogenetic tree and Bayesian integration model for three taxonomy levels of adenovirus including species, genus and type. The homology modeling method will be used to construct the three-dimensional structure model of the surface protein corresponding to the ancestral sequence. The stability of the viral capsid protein structure will be verified by molecular dynamics simulation and the optimal sequence for vector construction will be screened for. The coding region of the nucleic acid sequence corresponding to the surface protein of the ancestral adenovirus strain will be synthesized, then replacing the corresponding fragment in the genome of the commercial adenoviral vector, in order to construct a replication-defective vector hosting ancestral surface proteins, whose tropism and immunity would be verified at the cellular and animal level. Replication-deficient vectors can be used for disease control or treatment but cannot infect healthy animals or humans, so it would remain bio safe. The project will not only help us to understand the evolutionary history of adenoviruses' molecular biology, to explore the tropism in viral pathogenies, but also to develop new adenovirus vectors with bright future in translational medicine.