The SARS-CoV-2 Omicron variant has become the dominant SARS-CoV-2 variant around the world and exhibits immune escape to current COVID-19 vaccines to some extent due to its numerous spike mutations. Here, we evaluated the immune responses to booster vaccination with intramuscular adenovirus-vectored vaccine (Ad5-nCoV), aerosolized Ad5-nCoV, a recombinant protein subunit vaccine (ZF2001) or homologous inactivated vaccine (CoronaVac) in those who received two doses of inactivated COVID-19 vaccines 6 months prior. We found that the Ad5-nCoV booster induced potent neutralizing activity against the wild-type virus and Omicron variant, while aerosolized Ad5-nCoV generated the greatest neutralizing antibody responses against the Omicron variant at day 28 after booster vaccination, at 14.1-fold that of CoronaVac, 5.6-fold that of ZF2001 and 2.0-fold that of intramuscular Ad5-nCoV. Similarly, the aerosolized Ad5-nCoV booster produced the greatest IFNγ T-cell response at day 14 after booster vaccination. The IFNγ T-cell response to aerosolized Ad5-nCoV was 12.8-fold for CoronaVac, 16.5-fold for ZF2001, and 5.0-fold for intramuscular Ad5-nCoV. Aerosolized Ad5-nCoV booster also produced the greatest spike-specific B cell response. Our findings suggest that inactivated vaccine recipients should consider adenovirus-vectored vaccine boosters in China and that aerosolized Ad5-nCoV may provide a more efficient alternative in response to the spread of the Omicron variant.

T-cell immunity plays an important role in the control of SARS-CoV-2 and has a great cross-protective effect on the variants. The Omicron BA.1 variant contains more than 30 mutations in the spike and severely evades humoral immunity. To understand how Omicron BA.1 spike mutations affect cellular immunity, the T-cell epitopes of SARS-CoV-2 wild-type and Omicron BA.1 spike in BALB/c (H-2^d) and C57BL/6 mice (H-2^b) were mapped through IFNγ ELISpot and intracellular cytokine staining assays. The epitopes were identified and verified in splenocytes from mice vaccinated with the adenovirus type 5 vector encoding the homologous spike, and the positive peptides involved in spike mutations were tested against wide-type and Omicron BA.1 vaccines. A total of eleven T-cell epitopes of wild-type and Omicron BA.1 spike were identified in BALB/c mice, and nine were identified in C57BL/6 mice, only two of which were CD4⁺ T-cell epitopes and most of which were CD8⁺ T-cell epitopes. The A67V and Del 69-70 mutations in Omicron BA.1 spike abolished one epitope in wild-type spike, and the T478K, E484A, Q493R, G496S and H655Y mutations resulted in three new epitopes in Omicron BA.1 spike, while the Y505H mutation did not affect the epitope. These data describe the difference of T-cell epitopes in SARS-CoV-2 wild-type and Omicron BA.1 spike in H-2^b and H-2^d mice, providing a better understanding of the effects of Omicron BA.1 spike mutations on cellular immunity.

Background: Yiqi Zengmian (YQZM) functions as an immunopotentiator by enhancing both cellular and humoral immunity. However, its pharmacodynamic active constituents, particularly those absorbed into the bloodstream, and mechanism of action remain unclear. This study aimed to investigate the immunopotentiating effects and mechanisms of YQZM in mice immunized with the BBIBP-CorV (Beijing Bio-Institute of Biological Products Coronavirus Vaccine). Methods: Serum pharmacochemistry and ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) were employed to identify bioavailable components of YQZM. The mice received the BBIBP-CorV twice on days 1 and 14, while YQZM was orally administered for 28 days. Neutralization assays and ELISA quantified antigen-specific antibodies (abs), flow cytometry (FC) and intracellular cytokine staining (ICS) were used to assess immune cell populations and their cytokines, and an enzyme-linked immunospot assay (ELISpot) quantified memory T and B cells (MBs and MTs). To identify underlying mechanisms, network pharmacology, RNA sequencing (RNA-Seq), molecular docking, Western blotting (WB), and quantitative reverse transcription PCR (RT-qPCR) were performed. Results: YQZM significantly enhanced antigen-specific antibody titers, immune cell proportions, cytokine levels, and memory lymphocyte functions. UPLC-MS/MS analysis identified 31 bioactive compounds in YQZM. KEGG enrichment analysis based on RNA-Seq and network pharmacology implicated the TLR-JAK-STAT signaling pathway in YQZM’s immune-enhancing effects. WB and RT-PCR validated that YQZM upregulated the expression of critical nodes in the TLR-JAK-STAT signaling pathway. Furthermore, molecular docking indicated that YQZM’s primary active components exhibited strong binding affinity for critical proteins. Conclusions: YQZM effectively enhances vaccine-induced innate and adaptive immunity via a multi-component, multi-target mechanism, among which the TLR-JAK-STAT signaling pathway is a validated molecular target.