Development of a novel adenovirus type 4 vector as a promising respiratory vaccine vehicle

Jinghan Xu Busen Wang ^* Zhenghao Zhao Shipo Wu Zhe Zhang Shuling Liu Nan Huo Wanru Zheng Yi Chen Zhiqiang Gao Zuyuan Jia Tianyu Liu Li Zhu ^* Lihua Hou ^*

• Laboratory of Advanced Biotechnology, Beijing Institute of Biotechnology, Beijing, China

Introduction: Adenovirus (Ad) vectors are widely used for gene delivery, and some of them have been approved for vaccine development. In particular, the recombinant COVID-19 vaccine for inhalation, which was developed using adenovirus type 5 (Ad5), represents a milestone in respiratory immunization. Owing to the high pre-existing immunity (PEI) to Ad5, the development of an adenoviral vector with lower PEI and higher immunogenicity has been explored. However, most of the developed novel Ad vectors showed suboptimal immunogenicity in the animal model compared to Ad5.In this study, we constructed a novel replication-deficient viral vector based on human adenovirus type 4 (Ad4) which has long been used as a live virus vaccine with a favorable safety profile in the U.S. military. The mice were immunized intramuscularly or intranasally by Ad4 vectored vaccine to verify the immune responses and protective efficacy.Results: Compared with Ad5, the novel Ad4 vector showed comparable viral growth kinetics and transgene expression in cells and similar exogenous protein expression and distribution in mice. Besides, the Ad4-vectored vaccine elicited superior humoral and cellular responses as well as protective effects when vaccinated intranasally than those triggered by Ad5-vectored vaccine. Furthermore, the heterologous Ad5 prime and Ad4 boost immunization showed better immunogenicity and protection efficacy.Discussion: This study broadens the research trajectory of adenovirus-vectored vaccines and offers a new option for the development of recombinant viral-vectored vaccines.