CpG 684: an effective adjuvant for the inactivated COVID-19 vaccine in mice

Aim: This study used CpG 684 as adjuvant of inactivated COVID-19 vaccine to detect a humoral and cellular immune response in mice. Materials & methods: We used 10 and 20 µg CpG 684 as adjuvants of am inactivated COVID-19 vaccine to immunize mice. IgG, IgG1, IgG2a, IgG2b and IgM binding antibodies were detected in serum by ELISA. The IFN-γ cytokine was detected by ELISPOT. Results: CpG 684 improved spike-specific IgG and IgM subtype binding antibodies and increased the neutralizing antibody titer against prototype, Delta and Beta strains. CpG 684 also improved cellular immune response. Conclusion: CpG 684 is an effective adjuvant for inactivated COVID-19 vaccine.

A Novel Targeted RIG-I Receptor 5'Triphosphate Double Strain RNA-Based Adjuvant Significantly Improves the Immunogenicity of the SARS-CoV-2 Delta-Omicron Chimeric RBD-Dimer Recombinant Protein Vaccine.

The rapid mutation and spread of SARS-CoV-2 variants recently, especially through the emerging variants Omicron BA5, BF7, XBB and BQ1, necessitate the development of universal vaccines to provide broad spectrum protection against variants. For the SARS-CoV-2 universal recombinant protein vaccines, an effective approach is necessary to design broad-spectrum antigens and combine them with novel adjuvants that can induce high immunogenicity. In this study, we designed a novel targeted retinoic acid-inducible gene-I (RIG-I) receptor 5'triphosphate double strain RNA (5'PPP dsRNA)-based vaccine adjuvant (named AT149) and combined it with the SARS-CoV-2 Delta and Omicron chimeric RBD-dimer recombinant protein (D-O RBD) to immunize mice. The results showed that AT149 activated the P65 NF-κB signaling pathway, which subsequently activated the interferon signal pathway by targeting the RIG-I receptor. The D-O RBD + AT149 and D-O RBD + aluminum hydroxide adjuvant (Al) + AT149 groups showed elevated levels of neutralizing antibodies against the authentic Delta variant, and Omicron subvariants, BA1, BA5, and BF7, pseudovirus BQ1.1, and XBB compared with D-O RBD + Al and D-O RBD + Al + CpG7909/Poly (I:C) groups at 14 d after the second immunization, respectively. In addition, D-O RBD + AT149 and D-O RBD + Al + AT149 groups presented higher levels of the T-cell-secreted IFN-γ immune response. Overall, we designed a novel targeted RIG-I receptor 5'PPP dsRNA-based vaccine adjuvant to significantly improve the immunogenicity and broad spectrum of the SARS-CoV-2 recombinant protein vaccine.

Comparison of the immunogenicity of nasal-spray rVSV vector, adenovirus vector, and inactivated COVID-19-based vaccines in rodent models.

Intranasal (i.n.) vaccines can induce mucosal and systemic immunity against respiratory pathogens. Previously, we demonstrated that the recombinant vesicular stomatitis virus (rVSV)-based COVID-19 vaccine rVSV-SARS-CoV-2, with poor immunogenicity via the intramuscular route (i.m.), is more suitable for i.n. administration in mice and nonhuman primates. Here, we found that the rVSV-SARS-CoV-2 Beta variant was more immunogenic than the wild-type strain and other variants of concern (VOCs) in golden Syrian hamsters. Furthermore, the immune responses elicited by rVSV-based vaccine candidates via the i.n. route were significantly higher than those of two licensed vaccines: the inactivated vaccine KCONVAC delivered via the i.m. route and the adenovirus-based Vaxzevria delivered i.n. or i.m. We next assessed the booster efficacy of rVSV following two i.m. doses of KCONVAC. Twenty-eight days after receiving two i.m. doses of KCONVAC, hamsters were boosted with a third dose of KCONVAC (i.m.), Vaxzevria (i.m. or i.n.), or rVSVs (i.n.). Consistent with other heterologous booster studies, Vaxzevria and rVSV elicited significantly higher humoral immunity than the homogenous KCONVAC. In summary, our results confirmed that two i.n. doses of rVSV-Beta elicited significantly higher humoral immune responses than commercial inactivated and adeno-based COVID vaccines in hamsters. As a heterologous booster dose, rVSV-Beta induced potent, persistent, and broad-spectrum humoral and mucosal neutralizing responses against all VOCs, highlighting its potential to be developed into a nasal-spray vaccine.

A Novel Single-Stranded RNA-Based Adjuvant Improves the Immunogenicity of the SARS-CoV-2 Recombinant Protein Vaccine.

The research and development (R&D) of novel adjuvants is an effective measure for improving the immunogenicity of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recombinant protein vaccine. Toward this end, we designed a novel single-stranded RNA-based adjuvant, L2, from the SARS-CoV-2 prototype genome. L2 could initiate retinoic acid-inducible gene-I signaling pathways to effectively activate the innate immunity. ZF2001, an aluminum hydroxide (Al) adjuvanted SARS-CoV-2 recombinant receptor binding domain (RBD) subunit vaccine with emergency use authorization in China, was used for comparison. L2, with adjuvant compatibility with RBD, elevated the antibody response to a level more than that achieved with Al, CpG 7909, or poly(I:C) as adjuvants in mice. L2 plus Al with composite adjuvant compatibility with RBD markedly improved the immunogenicity of ZF2001; in particular, neutralizing antibody titers increased by about 44-fold for Omicron, and the combination also induced higher levels of antibodies than CpG 7909/poly(I:C) plus Al in mice. Moreover, L2 and L2 plus Al effectively improved the Th1 immune response, rather than the Th2 immune response. Taken together, L2, used as an adjuvant, enhanced the immune response of the SARS-CoV-2 recombinant RBD protein vaccine in mice. These findings should provide a basis for the R&D of novel RNA-based adjuvants.