Effects Of CPG-ODN On Immune Response Of Influenza Split Virion Vaccine

The widespread use of influenza vaccines is effective in the prevention and control of influenza epidemics. However, innovative vaccine technologies are still needed to improve the deficiencies of current influenza vaccines, such as the limited production capacity of pandemic vaccine, and the poor immunogenicity of seasonal vaccine in the infants and the elders. Adding adjuvants into vaccine formulations is the rational strategy to solve these problems. In the present study, the immuno-potentiating effect of a novel vaccine adjuvant, CpG oligodeoxynucleotides (CpG-ODN), on influenza split virion vaccine was evaluated.BALB/c mice were immunized intramuscularly or intranasally with 2009 H1N1 Influenza split virion vaccine using CpG-ODN, CpG-ODN plus Al(OH)3, or CpG-ODN plus Montanide ISA720 as adjuvants. Antigen-specific humoral immune responses were evaluated by ELISA, hemagglutination inhibiting (HI) assay and neutralizing assay. Antigen-specific cellular immune responses were evaluated by ELISPOT assay, intracellular cytokine staining assay and in vivo CTL assay.Intramuscular immunization results showed that compared with the control group immunized with antigen alone, CpG-ODN alone weakly enhanced the humoral immune responses, as indicated by the limited increase of antigen-specific IgG titers, HI titers and neutralizing titers by 3-6 folds, 2-4 folds and 4-8 folds, respectively, after two immunizations. In contrast, CpG-ODN plus Al(OH)3 as a composite adjuvant induced much more potent humoral immune responses; the antigen-specific IgG titers, HI titers and neutralizing titers were increased by 23-57 folds, 9-20 folds and 16-64 folds, respectively. Consequently, the composite adjuvant achieved antigen-sparing by at least 16 folds. In addition, the composite adjuvant enhanced the antigen-specific cellular immune responses, as revealed by the increase of IFN-γ-secreting CD4+ T cells and the increase of CD8+ CTL activity in immunized mice.Intranasal immuniziation results showed that CpG-ODN alone significantly enhanced the humoral immune responses compared with the control group, as indicated by the increase of antigen-specific serum IgG titers by 10 folds, after two or three immunizations. In addition, antigen-specific IgA was elicited in both serum and local mucosa. Furthermore, the single use of CpG-ODN enhanced the antigen-specific cellular immune responses to some extent, as revealed by the increase of IFN-γ-secreting CD4+ T cells and the increase of CD8+ CTL activity in immunized mice. However, neither CpG-ODN plus Al(OH)3 nor CpG-ODN plus Montanide ISA720 induced better immune responses compared with CpG-ODN.In conclusion: (1) CpG-ODN alone is an effective mucosal adjuvant for influenza split virion vaccine, enhancing not only mucosal but also systemic humoral and cellular immune responses; (2) CpG-ODN plus Al(OH)3 as a composite adjuvant for influenza split virion vaccine in intramuscular immunization strongly enhance the humoral and cellular immune responses and significantly reduce the dose of the antigen.