Live, attenuated influenza virus (LAIV) vehicles are strong inducers of immunity toward influenza B virus

Abstract

Historically, vaccines developed toward influenza viruses of the B type using methodologies developed for influenza A viruses as a blueprint have not been equally efficacious or effective. Because most influenza research and public attention concerns influenza A viruses, these shortcomings have not been adequately addressed. In this manuscript, we utilized different influenza vaccine vehicles to compare immunogenicity and protection in mice and ferrets after vaccination against an influenza B virus. We report that plasmid DNA vaccines demonstrate low immunogenicity profiles and poor protection compared to either whole, inactivated influenza virus (IIV) or, live, attenuated influenza virus (LAIV) vaccines. When mixed prime:boost regimens using LAIV and IIV were studied, we observed a boosting effect in mice after priming with LAIV that was not seen when IIV was used as the prime. In ferrets LAIV induced high antibody titers after a single dose and provided a boost in IIV-primed animals. Regimens including LAIV as a prime demonstrated enhanced protection, and adjuvantation was required for efficacy using the IIV preparation. Our results differ from generally accepted influenza A virus vaccine models, and argue that strategies for control of influenza B virus should be considered separately from those for influenza A virus.

Figure 1

Vaccination against influenza B virus with identical and mixed delivery vehicles induces IgG immunity in BALB/c mice. Sera taken from mice prior to vaccination (Pre), three weeks after primary (Pri), and three weeks after secondary (Sec) inoculation with influenza B virus HA expressed by identical (A) or mixed (B) vectors were analyzed for IgG isotypes (IgG (γ-specific), IgG1, or IgG2a) by ELISA. ELISA titers are reported as the reciprocal serum dilution representing 50% maximal binding on the titration curve. Titers are reported as the mean ± standard deviation for individual groups of mice at each time-point (Alum + Alum (◊), PBS + PBS (∇), n = 11; n = 18; HA-DNA (IM) + HA-DNA (IM) (∆), n = 18; HA-DNA (GG) + HA-DNA (GG) (□), n = 18;; IIV (Alum) + IIV (Alum) (●), n = 17; IIV + IIV (▼), n = 11;, LAIV + LAIV (■), n = 18, IIV + LAIV (▲), n = 11; and LAIV + IIV (◆), n = 11), except for Pre and Pri titers reported for the group receiving IIV + LAIV (n = 14).

Figure 2

Vaccination against influenza B virus with identical and mixed delivery vehicles induces protective immunity in BALB/c mice. Four weeks after secondary exposure to HA antigen expressed in multiple delivery vehicles, mice were challenged with 7.5 MLD₅₀ BYam98 HA-expressing virus with a mouse lethal phenotype. Morbidity (% initial body weight) and mortality (% survival) are reported for individual groups of mice (Alum + Alum (◊), PBS + PBS (∇), n = 11; n = 18; HA-DNA (IM) + HA-DNA (IM) (∆), n = 18; HA-DNA (GG) + HA-DNA (GG) (□), n = 18; IIV (Alum) + IIV (Alum) (●), n = 17; IIV + IIV (▼), n = 11;, LAIV + LAIV (■), n = 18, IIV + LAIV (▲), n = 11; and LAIV + IIV (◆), n = 11),

Figure 3

Vaccination against influenza B virus using mixed delivery vehicles induces disparate antibody kinetics. Sera taken from ferrets prior to vaccination (Pre), three weeks after primary (Pri) inoculation, and three weeks after secondary (Sec) inoculation with influenza B virus HA expressed by mixed vectors were analyzed for IgG (H + L) expression by ELISA. ELISA titers are reported as the reciprocal serum dilution representing 50% maximal binding on the titration curve. Titers for individual ferrets are reported as individual symbols, with the bar representing the mean for the (PBS (■), n = 2; IIV + LAIV (○), n = 4; and LAIV + IIV (◆), n = 4).

Figure 4

Nasal wash viral titers in vaccinated ferrets after challenge with BYam98 HA-expressing influenza virus. Nasal wash collected daily after challenge was tested for presence of influenza virus. Titers are reported as the mean ± standard deviation for each group at time-points indicated by the symbols (PBS (■), n = 2; IIV + LAIV (○), n = 4; and LAIV + IIV (◆), n = 4).