ABSTRACT
A safe and effective vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is urgently needed to tackle the COVID-19 global pandemic. Here, we describe the development of chimpanzee adenovirus serotypes 6 and 68 (AdC6 and AdC68) vector-based vaccine candidates expressing the full-length transmembrane spike glycoprotein. We assessed the vaccine immunogenicity, protective efficacy, and immune cell profiles using single-cell RNA sequencing in mice. Mice were vaccinated via the intramuscular route with the two vaccine candidates using prime-only regimens or heterologous prime-boost regimens. Both chimpanzee adenovirus-based vaccines elicited strong and long-term antibody and T cell responses, balanced Th1/Th2 cell responses, robust germinal center responses, and provided effective protection against SARS-CoV-2 infection in mouse lungs. Strikingly, we found that heterologous prime-boost immunization induced higher titers of protective antibodies, and more spike-specific memory CD8+ T cells in mice. Potent neutralizing antibodies produced against the highly transmissible SARS-CoV-2 variants B.1.1.7 lineage (also known as N501Y.V1) and B.1.351 lineage (also known as N501Y.V2) were detectable in mouse sera over 6 months after prime immunization. Our results demonstrate that the heterologous prime-boost strategy with chimpanzee adenovirus-based vaccines is promising for further development to prevent SARS-CoV-2 infection.
ABSTRACT
BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly pathogenic and contagious coronavirus that caused a global pandemic with 5.2 million fatalities to date. Questions concerning serologic features of long-term immunity, especially dominant epitopes mediating durable antibody responses after SARS-CoV-2 infection, remain to be elucidated. OBJECTIVE: We aimed to dissect the kinetics and longevity of immune responses in coronavirus disease 2019 (COVID-19) patients, as well as the epitopes responsible for sustained long-term humoral immunity against SARS-CoV-2. METHODS: We assessed SARS-CoV-2 immune dynamics up to 180 to 220 days after disease onset in 31 individuals who predominantly experienced moderate symptoms of COVID-19, then performed a proteome-wide profiling of dominant epitopes responsible for persistent humoral immune responses. RESULTS: Longitudinal analysis revealed sustained SARS-CoV-2 spike protein-specific antibodies and neutralizing antibodies in COVID-19 patients, along with activation of cytokine production at early stages after SARS-CoV-2 infection. Highly reactive epitopes that were capable of mediating long-term antibody responses were shown to be located at the spike and ORF1ab proteins. Key epitopes of the SARS-CoV-2 spike protein were mapped to the N-terminal domain of the S1 subunit and the S2 subunit, with varying degrees of sequence homology among endemic human coronaviruses and high sequence identity between the early SARS-CoV-2 (Wuhan-Hu-1) and current circulating variants. CONCLUSION: SARS-CoV-2 infection induces persistent humoral immunity in COVID-19-convalescent individuals by targeting dominant epitopes located at the spike and ORF1ab proteins that mediate long-term immune responses. Our findings provide a path to aid rational vaccine design and diagnostic development.