Superior immunogenicity of a freeze-dried, cell culture-derived Japanese encephalitis vaccine (inactivated)

Immunogenicity and safety of inactivated chromatographically purified Vero cell-derived Japanese encephalitis vaccine in Thai children

Summary: Inactivated mouse-brain-derived Japanese encephalitis vaccine has a worrisome safety profile and the live attenuated vaccine is unsuitable in immunodeficiency. This study aimed to evaluate the immunogenicity and safety of an inactivated chromatographically purified Vero-cell-derived JE vaccine (CVI-JE, Beijing P-3 strain) in children.

152 healthy Thai children, with an average (SD) age of 14.4 (3.8) months, received 3 doses of CVI-JE on days 0, 7–28, and one year. Homologous JE neutralizing antibody titers (NT) were measured. All subjects had seroprotection [geometric mean titer (GMT) 150] 28 days' post 2nd vaccination. The seroprotection rates at 1 year after primary series and and 1 month after the booster were 89.3% (GMT 49) and 100% (GMT 621), respectively. Local and systemic reactions–fever (17.6%), vomiting (8%), and poor appetite (5.3%)–were noted within 28 days' post-vaccination. All these symptoms were self-limited.

Conclusions: CVI-JE is safe, immunogenic, and provided high NT.

Japanese encephalitis vaccines: Immunogenicity, protective efficacy, effectiveness, and impact on the burden of disease

Japanese encephalitis (JE) is a serious public health concern in most of Asia. The disease is caused by JE virus (JEV), a flavivirus transmitted by Culex mosquitoes. Several vaccines have been developed to control JE in endemic areas as well as to protect travelers and military personnel who visit or are commissioned from non-endemic to endemic areas. The vaccines include inactivated vaccines produced in mouse brain or cell cultures, live attenuated vaccines, and a chimeric vaccine based on the live attenuated yellow fever virus 17D vaccine strain. All the marketed vaccines belong to the JEV genotype III, but have been shown to be efficacious against other genotypes and strains, with varying degrees of cross-neutralization, albeit at levels deemed to be protective. The protective responses have been shown to last three or more years, depending on the type of vaccine and the number of doses. This review presents a brief account of the different JE vaccines, their immunogenicity and protective ability, and the impact of JE vaccines in reducing the burden of disease in endemic countries.

The efficacy of inactivated West Nile vaccine (WN-VAX) in mice and monkeys

Background

West Nile virus (WNV) belonging to the genus Flavivirus of the family Flaviviridae causes nervous system disorder in humans, horses and birds. Licensed WNV vaccines are available for use in horses but not for humans. We previously developed an inactivated West Nile virus vaccine (WN-VAX) using a seed virus from West Nile virus (WNV NY99) that was originally isolated in New York City in 1999. In this study, we report the immunogenicity of WN-VAX in both mice and non-human primates.

Findings

The WN-VAX immunized mice showed protection against lethal infection with WNV NY99. The challenge test performed on mice passively immunized with serum from other mice that were previously immunized with WN-VAX confirmed that the neutralizing antibody titers of more than 1log10 protected the passively immunized mice from WNV lethal infection. Furthermore, monkeys (Macaca fascicularis) immunized three times with 2.5 μg, 5 μg or 10 μg/dose of WN-VAX exhibited neutralizing antibodies in their sera with titers of more than 2log10 after the second immunization.

Conclusions

The WN-VAX was protective in mice both by active and passive immunizations and was immunogenic in monkeys. These results suggest that the vaccine developed in this study may be a potential WNV vaccine candidate for human use.

Safety and immunogenicity of a freeze-dried, Vero cell culture-derived, inactivated Japanese encephalitis vaccine (KD-287, ENCEVAC®) versus a mouse brain-derived inactivated Japanese encephalitis vaccine in children: a phase III, multicenter, double-blinded, randomized trial

Background

Although mouse brain-derived, inactivated Japanese encephalitis vaccines (JE-MBs) have been successfully used for a long time, potential rare neurological complications have prompted the development of a Vero cell culture-derived inactivated vaccine (JE-VC). In a phase III clinical study, we aimed to compare the safety and immunogenicity of a JE-VC, KD-287 with a JE-MB, JEV-GCC, in children.

Methods

In this multicenter, double-blinded, randomized controlled trial, the study population consisted of 205 healthy Korean children aged 12–23 months. Each subject was subcutaneously vaccinated with either KD-287 or JEV-GCC twice at an interval of 2 weeks and then vaccinated once 12 months after the second vaccination. Neutralizing antibodies were measured by the plaque reduction neutralization test using the homologous and heterologous, as a post hoc analysis, challenge virus strains.

Results

The three-dose regimen of KD-287 showed a comparable safety profile with JEV-GCC except higher incidence of fever after the first dose (30.4% and 14.7%, respectively). Most of the fever was mild degree (61.3% and 66.7%, respectively). KD-287 fulfilled the non-inferiority criteria for seroconversion rate (SCR) and geometric mean titer (GMT) of the neutralizing antibody, which were the primary endpoints, at 4 weeks after the third vaccination (95% CI: −1.00, 3.10 for the SCR difference and 10.8, 17.6 for the GMT ratio). The SCRs of KD-287 were all 100% and the GMTs were higher in the KD-287 group than in the JEV-GCC group after the second vaccination and before and after the third vaccination (GMT ratio: 5.59, 20.13, and 13.79, respectively, p < 0.001 in all). GMTs were higher in the KD-287 group in the heterologous analysis also (GMT ratio: 4.05, 5.15, and 4.19, respectively, p < 0.001 in all).

Conclusions

This study suggests that the KD-287, a JE-VC is as safe as and may be more effective than the licensed MB-derived vaccine. KD-287 could thus be useful as a second-generation vaccine and substitute for the current JE-MB vaccine in Korean children.

Trial registration

ClinicalTrials.gov: NCT01150942

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0744-4) contains supplementary material, which is available to authorized users.

Generation and characterization of a new mammalian cell line continuously expressing virus-like particles of Japanese encephalitis virus for a subunit vaccine candidate

Background

Japanese encephalitis virus (JEV) is the most important cause of epidemic encephalitis in most Asian regions. There is no specific treatment available for Japanese encephalitis, and vaccination is the only effective way to prevent JEV infection in humans and domestic animals. The purpose of this study is to establish a new mammalian cell line stably and efficiently expressing virus-like particle of JEV for potential use of JEV subunit vaccine.

Results

We generated a new cell clone (BJ-ME cells) that stably produces a secreted form of Japanese encephalitis virus (JEV) virus-like particle (VLP). The BJ-ME cells were engineered by transfecting BHK-21 cells with a code-optimized cDNA encoding JEV prM and E protein expression plasmid. Cell line BJ-ME can stably produces a secreted form of Japanese encephalitis virus virus-like particle (JEV-VLP) which contains the JEV envelope glycoprotein (E) and membrane protein (M). The amount of JEV-VLP antigen released into the culture fluid of BJ-ME cells was as high as 15–20 μg/ml. JEV-VLP production was stable after multiple cell passages and 100% cell expression was maintained without detectable cell fusion or apoptosis. Cell culture fluid containing the JEV-VLP antigen could be harvested five to seven times continuously at intervals of 4–6 days while maintaining the culture. Mice immunized with the JEV-VLP antigen with or without adjuvant developed high titers of neutralizing antibodies and 100% protection against lethal JEV challenge.

Conclusion

These results suggest that the recombinant JEV-VLP antigen produced by the BJ-ME cell line is an effective, safe and affordable subunit Japanese encephalitis vaccine candidate, especially for domestic animals such as pig and horse.

Long-term follow-up after reimplantation of tumorous mandible bone treated with combination of decalcification and lyophilization

Mandibular resection requires reconstruction, with often unsatisfactory morphofunctional results. Reimplantation of the resected mandible itself is one of ideal solutions to this problem. However, both devitalization of tumor cells involved in resected bone and preservation of osteoinductive activity are required for successful results. Lyophilization appears to enable devitalization of tumor cells, and decalcified bone implants are likely to have osteoinductive potential. Accordingly, we speculated that decalcification and lyophilization of resected bone would be an appropriate method for mandibular reconstruction. However, there is no study on the reimplantation of mandibles treated with these methods to date. The purpose of this study was to estimate the long-term follow-up of reimplanted mandibles treated with decalcification and lyophilization. Presented here are 2 patients of reimplanted mandibles treated by decalcification and lyophilization who were followed up for 8 and 9 years. We observed a good incorporation of the graft in 1 case, but severe absorption in the other. Our results suggest that treatment with decalcification and lyophilization is 1 strategy for reimplantation of the resected bone in mandibular reconstruction, but further study is needed to prevent absorption of the reimplanted bone over the long term.

Immunogenicity of single-dose Vero cell-derived Japanese encephalitis vaccine in Japanese adults

In Japan, intensive immunization against Japanese encephalitis (JE) was performed from 1967 to 1976, and regular JE immunization was performed thereafter. However, for Japanese adults facing JE risk, dates of vaccination with new inactivated Vero cell-derived JE vaccine are unavailable. This study investigated how a single dose of Vero cell-derived JE vaccine affects Japanese adults. Neutralizing antibodies were measured pre- and post-JE vaccination in 79 participants (age 40.7 ± 9.4 years), enrolled between October 2009 and March 2011, whose JE-vaccination data were gathered from vaccination records and history taking. Before vaccination, the participants' seroprotection rate (SPR) was 51.9%, whereas SPR after vaccination was 93.7%. The seroconversion rate (SCR), which measures seronegative cases that turn seropositive after vaccination, was 86.8%. The geometric mean titer (GMT) was 14.7 before vaccination and 70.1 after vaccination. Age was a significant difference between seroprotected (42.8 years) and non-seroprotected (38.7 years) groups before vaccination. Then the difference of age, SCR, pre-vaccination GMT, post-vaccination GMT and sex ratio were also significant in participants aged 25-39 years and ≥40 years, who represent generations born when Japan's JE-vaccination policy changed. SCR was 100% in participants aged 25-39 years with a vaccination recorded 55.6% in participants aged 25-39 without a vaccination record, and 96.0% in participants aged ≥40 years. Thus, more participants aged 25-39 years were seroprotected before vaccination, but SCR was higher in those aged ≥40 years. Most Japanese adults can be protected after one-dose vaccination, but this may be insufficient for people aged 25-39 years without recorded JE vaccination.

A review of successful flavivirus vaccines and the problems with those flaviviruses for which vaccines are not yet available

Genus flavivirus comprises many important human pathogens causing public health problems worldwide. Some flavivirus infections are characterized by a relatively high mortality rate and/or high sequelae rate in survivors. Because most flavivirus life cycles are maintained between arthropod vectors and amplifying/reservoir hosts in the absence of humans, eradication of flaviviruses might be extremely difficult. Flavivirus vaccine development is considered a reasonable method to prevent flavivirus infections. Some vaccines have been successfully developed, but others have not, regardless of much effort. This review article describes currently available flavivirus vaccines against yellow fever, Japanese encephalitis, and tick-borne encephalitis. In addition, the current status of dengue and West Nile virus vaccine development is reviewed and problems regarding their development are discussed.

Suitability and perspectives on using recombinant insect cells for the production of virus-like particles

Virus-like particles (VLPs) can be produced in recombinant protein production systems by expressing viral surface proteins that spontaneously assemble into particulate structures similar to authentic viral or subviral particles. VLPs serve as excellent platforms for the development of safe and effective vaccines and diagnostic antigens. Among various recombinant protein production systems, the baculovirus-insect cell system has been used extensively for the production of a wide variety of VLPs. This system is already employed for the manufacture of a licensed human papillomavirus-like particle vaccine. However, the baculovirus-insect cell system has several inherent limitations including contamination of VLPs with progeny baculovirus particles. Stably transformed insect cells have emerged as attractive alternatives to the baculovirus-insect cell system. Different types of VLPs, with or without an envelope and composed of either single or multiple structural proteins, have been produced in stably transformed insect cells. VLPs produced by stably transformed insect cells have successfully elicited immune responses in vivo. In some cases, the yield of VLPs attained with recombinant insect cells was comparable to, or higher than, that obtained by baculovirus-infected insect cells. Recombinant insect cells offer a promising approach to the development and production of VLPs.

Immunogenicity and safety of currently available Japanese encephalitis vaccines: a systematic review

A number of Japanese encephalitis (JE) vaccines have been used for preventing Japanese encephalitis around the world. We here reviewed the immunogenicity and safety of the currently available Japanese encephalitis vaccines. We searched Pubmed, Embase, Web of Science, the Cochrane Library and other online databases up to March 25, 2014 for studies focusing on currently used JE vaccines in any language. The primary outcomes were the seroconversion rate against JEV and adverse events. Meta-analysis was performed for the primary outcome when available. A total of 51 articles were included. Studies were grouped on the basic types of vaccines. This systematic review led to 2 aspects of the conclusions. On one hand, all the currently available JE vaccines are safe and effective. On the other hand, the overall of JE vaccine evaluation is disorganized, the large variation in study designs, vaccine types, schedules, doses, population and few hand-to-hand trails, make direct comparisons difficult. In order to make a more evidence-based decision on optimizing the JE vaccine, it is warranted to standardize the JE vaccine evaluation research.

Phase III clinical trials comparing the immunogenicity and safety of the vero cell-derived Japanese encephalitis vaccine Encevac with those of mouse brain-derived vaccine by using the Beijing-1 strain

The immunogenicity and safety of an inactivated cell culture Japanese encephalitis vaccine (CC-JEV) were compared with those of an inactivated mouse brain-derived Japanese encephalitis vaccine (MB-JEV) in phase III clinical multicenter trials conducted in children. The vaccines contain the same Japanese encephalitis virus strain, the Beijing-1 strain. Two independent clinical trials (trials 1 and 2) were conducted. Trial 1 was conducted in 468 healthy children. Each subject was injected with 17 μg per dose of either CC-JEV or MB-JEV, and the immunogenicity and safety of the vaccines were investigated. Trial 1 showed that CC-JEV was more immunogenic and reactive than MB-JEV at the same dose. Therefore, to adjust the immunogenicity of CC-JEV to that of MB-JEV, a vaccine that has had a good track record regarding its efficacy for a long time, trial 2 was conducted in 484 healthy children. To improve the stability, CC-JEV was converted from a liquid type to a freeze-dried type of vaccine. Each subject was injected subcutaneously with either 4 μg per dose of CC-JEV, 8 μg per dose of CC-JEV, or 17 μg per dose of MB-JEV twice, at an interval of 2 to 4 weeks, followed by an additional booster immunization 1 to 15 months after the primary immunization. Based on the results of trial 2, 4 μg per dose of the freeze-dried CC-JEV (under the label Encevac) was selected as a substitute for the MB-JEV. Encevac was approved and launched in 2011 and has since been in use as a 2nd-generation Japanese encephalitis vaccine in Japan. (These studies have been registered at the JapicCTI under registration no. JapicCTI-132063 and JapicCTI-080586 for trials 1 and 2, respectively).

Japanese encephalitis: the virus and vaccines

Japanese encephalitis (JE) is an infectious disease of the central nervous system caused by Japanese encephalitis virus (JEV), a zoonotic mosquito-borne flavivirus. JEV is prevalent in much of Asia and the Western Pacific, with over 4 billion people living at risk of infection. In the absence of antiviral intervention, vaccination is the only strategy to develop long-term sustainable protection against JEV infection. Over the past half-century, a mouse brain-derived inactivated vaccine has been used internationally for active immunization. To date, however, JEV is still a clinically important, emerging, and re-emerging human pathogen of global significance. In recent years, production of the mouse brain-derived vaccine has been discontinued, but 3 new cell culture-derived vaccines are available in various parts of the world. Here we review current aspects of JEV biology, summarize the 4 types of JEV vaccine, and discuss the potential of an infectious JEV cDNA technology for future vaccine development.

Production of Japanese encephalitis virus-like particles in insect cells

Virus-like particles (VLPs) are composed of one or several recombinant viral surface proteins that spontaneously assemble into particulate structures without the incorporation of virus DNA or RNA. The baculovirus-insect cell system has been used extensively for the production of recombinant virus proteins including VLPs. While the baculovirus-insect cell system directs the transient expression of recombinant proteins in a batch culture, stably transformed insect cells allow constitutive production. In our recent study, a secretory form of Japanese encephalitis (JE) VLPs was successfully produced by Trichoplusia ni BTI-TN-5B1-4 (High Five) cells engineered to coexpress the JE virus (JEV) premembrane (prM) and envelope (E) proteins. A higher yield of E protein was attained with recombinant High Five cells than with the baculovirus-insect cell system. This study demonstrated that recombinant insect cells offer a promising approach to the high-level production of VLPs for use as vaccines and diagnostic antigens.