Prime-boost vaccination of mice and Rhesus macaques with two novel adenovirus vectored COVID-19 vaccine candidates

Luo, Shengxue; Zhang, Panli; Liu, Bochao; Yang, Chan; Liang, Chaolan; Wang, Qi; Zhang, Ling; Tang, Xi; Li, Jinfeng; Hou, Shuiping; Zeng, Jinfeng; Fu, Yongshui; Allain, Jean-Pierre; Li, Tingting; Zhang, Yuming; Li, Chengyao

COVID-19 vaccines are being developed urgently worldwide, among which single-shot adenovirus vectored vaccines represent a major approach. Here, we constructed two novel adenovirus vectored COVID-19 vaccine candidates on simian adenovirus serotype 23 (Sad23L) and human adenovirus serotype 49 vectors (Ad49L) carrying the full-length gene of SARS-CoV-2 spike protein (S), designated Sad23L-nCoV-S and Ad49L-nCoV-S vaccines, respectively. The immunogenicity elicited by these two vaccine strains was individually evaluated in mice. Specific humoral and cellular immune responses were proportionally observed in a dose-dependent manner, and stronger response was obtained by boosting. Furthermore, five rhesus macaques were intramuscularly injected with a dose of 5×109 PFU Sad23L-nCoV-S vaccine for prime vaccination, followed by boosting with 5×109 PFU of Ad49L-nCoV-S vaccine at 4-week interval. Three macaques were injected with Sad23L-GFP and Ad49L-GFP vectorial viruses as negative controls. Both mice and macaques tolerated well the vaccine inoculations without detectable clinical or pathologic changes. In macaques, prime-boost vaccination regimen induced high titers of 103.16 S-binding antibody (S-BAb), 102.75 cell receptor binding domain (RBD)-BAb and 102.38 neutralizing antibody (NAb) to pseudovirus a week after boosting injection, followed by sustained high levels over 10 weeks of observation. Robust IFN-γ secreting T-cell response (712.6 SFCs/106 cells), IL-2 secreting T-cell response (334 SFCs/106 cells) and intracellular IFN-γ expressing CD4+/CD8+ T cell response (0.39%/0.55%) to S peptides were detected in the vaccinated macaques. It was concluded that prime-boost immunization with Sad23L-nCoV-S and Ad49L-nCoV-S vaccines can safely elicit strong immunity in animals in preparation of clinical phase 1/2 trials.