Intranasal Immunization with a Formalin-Inactivated Human Influenza A Virus Whole-Virion Vaccine Alone and Intranasal Immunization with a Split-Virion Vaccine with Mucosal Adjuvants Show Similar Levels of Cross-Protection

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>The antigenicity of seasonal human influenza virus changes continuously; thus, a cross-protective influenza vaccine design needs to be established. Intranasal immunization with an influenza split-virion (SV) vaccine and a mucosal adjuvant induces cross-protection; however, no mucosal adjuvant has been assessed clinically. Formalin-inactivated intact human and avian viruses alone (without adjuvant) induce cross-protection against the highly pathogenic H5N1 avian influenza virus. However, it is unknown whether seasonal human influenza formalin-inactivated whole-virion (WV) vaccine alone induces cross-protection against strains within a subtype or in a different subtype of human influenza virus. Furthermore, there are few reports comparing the cross-protective efficacy of the WV vaccine and SV vaccine-mucosal adjuvant mixtures. Here, we found that the intranasal human influenza WV vaccine alone induced both the innate immune response and acquired immune response, resulting in cross-protection against drift variants within a subtype of human influenza virus. The cross-protective efficacy conferred by the WV vaccine in intranasally immunized mice was almost the same as that conferred by a mixture of SV vaccine and adjuvants. The level of cross-protective efficacy was correlated with the cross-reactive neutralizing antibody titer in the nasal wash and bronchoalveolar fluids. However, neither the SV vaccine with adjuvant nor the WV vaccine induced cross-reactive virus-specific cytotoxic T-lymphocyte activity. These results suggest that the intranasal human WV vaccine injection alone is effective against variants within a virus subtype, mainly through a humoral immune response, and that the cross-protection elicited by the WV vaccine and the SV vaccine plus mucosal adjuvants is similar.</jats:p>

An MDCK Cell Culture-Derived Formalin-Inactivated Influenza Virus Whole-Virion Vaccine from an Influenza Virus Library Confers Cross-Protective Immunity by Intranasal Administration in Mice

“…Intranasal immunization with gammaradiation-inactivated whole-virion influenza vaccine induces influenza virus-specific cross-reactive humoral and cellular immunity (44,45). On the other hand, formalin-inactivated whole-virion influenza vaccine induces cross-reactive humoral immunity but rarely cellular immunity (24,45). Furthermore, cross-reactive neutralizing antibodies contribute to the cross-protection caused by intranasal immunization with formalin-inactivated whole-virion vaccine, and cross-reactive neutralization by intranasal immunization with a formalin-inactivated H1N1 influenza virus vaccine includes drift variants within the influenza virus subtype (24).…”

“…On the other hand, formalin-inactivated whole-virion influenza vaccine induces cross-reactive humoral immunity but rarely cellular immunity (24,45). Furthermore, cross-reactive neutralizing antibodies contribute to the cross-protection caused by intranasal immunization with formalin-inactivated whole-virion vaccine, and cross-reactive neutralization by intranasal immunization with a formalin-inactivated H1N1 influenza virus vaccine includes drift variants within the influenza virus subtype (24). However, Takada et al demonstrated that formalin-inactivated H5N1 influenza whole-virion vaccine in intranasal immunization does not induce cross-protection against different influenza virus subtypes through cross-reactive neutralizing antibodies (25).…”

“…After a 1-h incubation, the cells were washed 3 times with complete RPMI 1640 medium. For cytotoxicity assays, the infected P815 cells were labeled with Na 51 CrO 4 (PerkinElmer, Waltham, MA) as described previously (24). The target cells were suspended at 10 5 cells/ml in complete RPMI 1640 medium for use in the CTL assay.…”

“…Neutralizing antibody titers in the mouse sera and bronchoalveolar lavage (BAL) fluids were determined by a micro-cytopathic effect neutralizing test (21,24). The gamma interferon (IFN-␥) ELISPOT assay was performed as described previously (21,28).…”

“…In animal models, intranasal immunization with an influenza virus split-virion vaccine with mucosal adjuvant [e.g., cholera toxin B, poly(I-C), or poly(␥-glutamic acid) nanoparticles] induces cross-protection and in vivo virus clearance against drift variants within a subtype and against different subtypes of virus (19)(20)(21)(22)(23). Furthermore, intranasal immunization of mice with formalin-inactivated intact virus alone (without adjuvant), but not with an ether-split vaccine alone, induces cross-protection against the homologous virus, intrasubtype variants, and influenza A viruses of different subtypes (24,25).…”