An inactivated hand-foot-and-mouth disease vaccine using the enterovirus 71 (C4a) strain isolated from a Korean patient induces a strong immunogenic response in mice

Abstract

Enterovirus 71 (EV71) is a major causative agent of hand-foot-and-mouth disease (HFMD) frequently occurring in children. HFMD induced by EV71 can cause serious health problems and has been reported worldwide, particularly in the Asia-Pacific region. In this study, we assessed the immunogenicity of a formalin-inactivated HFMD vaccine using an EV71 strain (FI-EV71 C4a) isolated from a Korean patient. The vaccine candidate was evaluated in mice to determine the vaccination doses and vaccine schedules. BALB/c mice were intramuscularly administered 5, 10, or 20 μg FI-EV71 vaccine, followed by a booster 2 weeks later. EV71-specific antibodies and neutralizing antibodies were induced and maintained until the end of the experimental period in all vaccinated groups. To determine the effectiveness of adjuvant for the EV71 vaccine, three adjuvants, i.e., aluminium hydroxide gel, monophosphoryl lipid A, and polyinosinic-polycytidylic acid, were administered separately with the FI-EV71 vaccine to mice via the intramuscular route. Mice administered the FI-EV71 vaccine formulated with all three adjuvants induced a significantly increased antibody response compared with that of the single adjuvant groups. The vaccinated group with triple adjuvants exhibited more rapid induction of EV71-specific and neutralizing antibodies than the other groups. These results suggested that the role of adjuvant in inactivated vaccine was important for eliciting effective immune responses against EV71. In conclusion, our results showed that FI-EV71 was a potential candidate vaccine for prevention of EV71 infection.

Fig 1. EV71-specific humoral immune responses induced by a formalin-inactivated EV71 vaccine in mice.

Mice were administered inactivated EV71 vaccine mixed with 500 μg for alum, 2 μg for MPLA, and 10 μg for poly I:C adjuvant or PBS as a control. (A) Titers of total IgG antibodies against EV71 viral particles were determined by ELISAs. (B) The levels of neutralization antibodies against EV71 were measured by endpoint dilution of serum in neutralization assays.

Fig 2. EV71-specific cell mediated immune responses induced by a formalin-inactivated EV71 vaccine in mice.

Mice were administered inactivated EV71 vaccine mixed with 500 μg for alum, 2 μg for MPLA, and 10 μg for poly I:C adjuvant or PBS as a control. Splenocytes from vaccinated mice were isolated and stimulated with the EV71 vaccine. The supernatants of splenocytes were harvested at 48 h after stimulation and analyzed for cytokines using a multiplex system. Graphs show means + SEMs. *p < 0.01, using one-way ANOVA with Tukey’s post-hoc test.

Fig 3. EV71-specific immune responses in serum samples from mice vaccinated with the formalin-inactivated EV71 vaccine combined with diverse adjuvants.

Mice were administered the inactivated EV71 vaccine mixed with 500 μg for alum, 2 μg for MPLA, and 10 μg for poly I:C adjuvant. (A) The lgG antibody titer against EV71 was measured by ELISA at 4, 8, 12 and 16 weeks. (B) IgG isotype analysis of EV71-specific IgGs in sera of mice at 8 weeks postvaccination. The IgG isotype graph shows means + SEMs. ***p < 0.0001 using one-way ANOVA with Tukey’s post-hoc test.

Fig 4. EV71-specific immune responses in serum samples from mice vaccinated with the formalin-inactivated EV71 vaccine combined with diverse adjuvants.

Mice were administered the inactivated EV71 vaccine mixed with 500 μg for alum, 2 μg for MPLA, and 10 μg for poly I:C adjuvant and measurement of neutralization antibody titer(A) and cross-reactivity of neutralization antibodies (B) by heterologous EV71 strains. Crossreactivity was determined using sera from mice at 16 weeks postvaccination. ***p < 0.0001 using one-way ANOVA with Tukey’s post-hoc test.

Fig 5. EV71-specific cell mediated immune responses induced by the formalin-inactivated EV71 vaccine with diverse adjuvants.

Splenocytes from vaccinated mice were isolated and stimulated with the EV71 vaccine strain. Supernatants of splenocytes were harvested at 48 h after stimulation and analyzed for cytokine levels using a multiplex system. Graphs show means + SEMs. *p < 0.01, using one-way ANOVA with Tukey’s post-hoc test.