Long-term immunogenicity studies of formalin-inactivated enterovirus 71 whole-virion vaccine in macaques.

Enterovirus 71 (EV71) has caused epidemics of hand, foot and mouth diseases in Asia during the past decades and no vaccine is available. A formalin-inactivated EV71 candidate vaccine (EV71vac) based on B4 subgenotype has previously been developed and found to elicit strong neutralizing antibody responses in mice and humans. In this study, we evaluated the long-term immunogenicity and safety of this EV71vac in a non-human primate model. Juvenile macaques were immunized at 0, 3 and 6 weeks either with 10 or 5 µg doses of EV71vac formulated with AlPO4 adjuvant, or PBS as control. During the 56 weeks of studies, no fever nor local redness and swelling at sites of injections was observed in the immunized macaques. After single immunization, 100% seroconversion based on 4-fold increased in neutralization titer (Nt) was detected in EV71vac immunized monkeys but not PBS controls. A dose-dependent IgG antibody response was observed in monkeys receiving EV71vac immunization. The Nt of EV71vac immunized macaques had reached the peak after 3 vaccinations, then decreased gradually; however, the GMT of neutralizing antibody in the EV71vac immunized macaques were still above 100 at the end of the study. Correspondingly, both dose- and time-dependent interferon-γ and CD4+ T cell responses were detected in monkeys receiving EV71vac. Interestingly, similar to human responses, the dominant T cell epitopes of macaques were identified mainly in VP2 and VP3 regions. In addition, strong cross-neutralizing antibodies against most EV71 subgenotypes except some C2 and C4b strains, and Coxsackievirus A16 were observed. In summary, our results indicate that EV71vac elicits dose-dependent T-cell and antibody responses in macaques that could be a good animal model for evaluating the long-term immune responses elicited by EV71 vaccines.

A consensus envelope protein domain III can induce neutralizing antibody responses against serotype 2 of dengue virus in non-human primates.

We have previously demonstrated that vaccination with a subunit dengue vaccine containing a consensus envelope domain III with aluminum phosphate elicits neutralizing antibodies against all four serotypes of dengue virus in mice. In this study, we evaluated the immunogenicity of the subunit dengue vaccine in non-human primates. After vaccination, monkeys that received the subunit vaccine with aluminum phosphate developed a significantly strong and long-lasting antibody response. A specific T cell response with cytokine production was also induced, and this correlated with the antibody response. Additionally, neutralizing antibodies against serotype 2 were detected in two of three monkeys. The increase in serotype-2-specific antibody titers and avidity observed in these two monkeys suggested that a serotype-2-biased antibody response occurs. These data provide evidence that a protective neutralizing antibody response was successfully elicited in non-human primates by the dengue subunit vaccine with aluminum phosphate adjuvant.

Serologic profiles of chickens infected with subgroup J avian leukosis virus.

Subgroup J avian leukosis virus (ALV-J) causes serious economic losses in the commercial poultry industry. Measuring group-specific antigen (GSA) by enzyme-linked immunosorbent assay (ELISA) has been used to identify chickens infected with this virus. However, the inability of ELISA to discriminate the GSA from endogenous ALV (subgroup E ALV [ALV-E]) or ALV-J infection has limited its usage. The purpose of the present study was to develop a method to discriminate between uninfected flocks having ALV-E and ALV-J-infected flocks by ELISA. The GSA and anti-ALV-J antibody in the plasma samples from chickens at different ages in three grandparent farms were measured by ELISA. Infected flocks were confirmed by reverse transcription-polymerase chain reaction with different subgroup-specific primers and sequence analysis. The results indicated that the GSA of ALV-J-infected flocks increased, but that of the uninfected flocks decreased during young ages. The anti-ALV-J antibody of infected flocks was higher and increased earlier than that of uninfected flocks. Thus, measuring GSA in blood at the ages of 1 and 6 wk by ELISA is suitable to discriminate between ALV-J-infected flocks and uninfected flocks having ALV-E.