Immunogenicity and safety of single booster dose of KD-414 inactivated COVID-19 vaccine in adults: An open-label, single-center, non-randomized, controlled study in Japan.

Although vaccines for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease 2019 (COVID-19) induce effective immune responses, vaccination with booster doses is necessary because of waning immunity. We conducted an open-label, non-randomized, single-arm study in adults in Japan to assess the immunogenicity and safety of a single booster dose of the KD-414 purified whole-SARS-CoV-2-virion inactivated vaccine candidate after vaccination with a primary series of BNT162b2. The primary endpoint was serum neutralizing activity at 7 days after booster injection compared with the primary series of BNT162b2. The SARS-CoV-2-structural protein-binding antibody level and T cell response against SARS-CoV-2-Spike (S) peptides were also examined as secondary endpoints, and safety profile assessments were conducted. Twenty subjects who participated in a previous study declined an injection of KD-414 (non-KD-414 group) and received a booster dose of BNT162b2 instead. The non-KD-414 group was compared to the KD-414 group as a secondary outcome. A single dose of KD-414 induced lower serum neutralizing activity against the wild-type virus within 7 days compared to after the primary series of BNT162b2 but significantly induced anti-SARS-CoV-2-S1-receptor-binding domain-binding immunoglobulin G (IgG) antibodies and SARS-CoV-2-S peptide-specific CD4+ and CD8+ T cell responses. Local or systemic symptoms were significantly lower in the participants who received KD-414 than in those who received BNT162b2 as the third COVID-19 vaccine dose. The present data indicate that a single booster dose of KD-414 induces a substantial immune response in BNT162b2-primed individuals and has a good safety profile, thereby supporting further clinical trials to identify rational targets.

Persistence of neutralizing antibody and its protective efficacy induced by a live attenuated tetravalent dengue vaccine, KD-382, in cynomolgus monkeys.

An effective dengue vaccine should induce a long-lasting immune response against all four serotypes simultaneously with a minimum number of immunizations. Our live attenuated tetravalent dengue vaccine candidate, KD-382, was developed using a classical host range mutation strategy (no addition of artificial genetic modification). In our previous study, cynomolgus monkeys immunized with a single dose of KD-382 seroconverted to all four serotypes. However, it is important to determine if neutralizing antibodies (NAbs) induced by KD-382 can work as a long-lasting immune response to prevent dengue. In this study, a single dose of KD-382 induced a strong NAb response against all four serotypes in cynomolgus monkeys. We also confirmed that NAb titers against all four serotypes persist for at least five years, indicating its high potential as a dengue vaccine candidate. Next, we evaluated the effect of pre-existing dengue immunity on NAb responses induced by KD-382. We administered KD-382 to cynomolgus monkeys pre-administered one of the monovalent parental wild-type strains 60 days before vaccination. Regardless of the pre-immunized serotype, all the monkeys showed sufficient tetravalent NAb responses, which lasted for over two years. All the KD-382 vaccinated monkeys were then challenged with different parental wild-type viruses than that used for pre-administration; viral RNA in the serum was less than the lower limit of quantification, indicating complete protection against secondary heterologous dengue infection without any harmful disease enhancement. Consequently, KD-382 successfully induced a long-lasting and protective tetravalent NAb response in monkeys, suggesting that KD-382 is a promising vaccine candidate usable for both dengue seronegative and seropositive individuals.

Well-balanced immune response and protective efficacy induced by a single dose of live attenuated tetravalent dengue vaccine (KD-382) in monkeys.

One of the challenges developing a live attenuated tetravalent dengue vaccine (TDV) is to overcome the presumed viral interference that may be preventing the induction of a balanced immune response to all 4 serotypes of the dengue virus (DENV1-4). Our live attenuated TDV candidate was developed from wild-type (wt) parental strains (DENV1/03135, DENV2/99345, DENV3/16562, and DENV4/1036, respectively) using a classical host range mutation strategy: the same strategy used for the approved live attenuated smallpox, polio, and MMR vaccines. Our vaccine candidate is expected to mimic natural dengue virus infection, as it provides all the components of dengue virus, including both structural and nonstructural proteins. Therefore, induction of more solid and comprehensive immune responses against pathogenic dengue viruses is also expected. In this study, we evaluated the neutralizing antibody responses for each serotype induced by a single subcutaneous administration of 6 formulations, which were composed of different combinations of vaccine strains and were all of different dosages. These formulations were tested in dengue-naïve cynomolgus macaques. As a result, regardless of the TDV formulation, all the monkeys immunized with TDVs seroconverted to all the 4 serotypes at day 30. Next, we evaluated protection ability of the selected formulations of TDV candidate, no RNAemia was detected from any of the immunized monkeys upon s.c. challenge with wtDENV. The findings of this non-human primate study indicate that our vaccine candidate is very promising; it can be further evaluated for safety and efficacy in human clinical studies.

Immunological equivalence between mouse brain-derived and Vero cell-derived Japanese encephalitis vaccines.

The persistent spread via animal reservoirs urges expanding vaccination programs against pathogens like the Japanese encephalitis virus, JEV. The JEV is spreads to new areas by domestic as well as by wild animals. Although there is a safe and efficient vaccine on the market, this is derived from infected mouse brains, why today's situation requires overcoming the potential risk caused by using animal tissues. To meet this demand we have developed a Vero cell-derived JEV vaccine, using the same virus strain as in the established one. A phase III clinical study of the new vaccine has recently been completed with positive outcome. Like the established mouse brain-derived vaccine, the Vero cell-derived one is a formalin inactivated whole virus vaccine. We here demonstrate the very good agreement in immunological tests between the two antigens. The study includes analyses with two neutralizing monoclonal antibodies that blocks cell entry at a late stage in infection, assumedly interfering with fusion-related refolding in the virus fusion protein. It is obvious that the formalin inactivation treatment, with both virus preparations, retains these essential vaccine epitopes.

Development of Vero cell-derived inactivated Japanese encephalitis vaccine.

We have established a manufacturing system for a Vero cell-derived inactivated Japanese encephalitis vaccine at a 500l scale. The production system involves expansion of Vero cells using microcarrier, followed by virus infection. Except for an additional purification step, the downstream purification processes are similar to those used for the current mouse brain-derived vaccine; cell removal, concentration and removal of low-molecular weight impurities by membrane filtration, formalin-inactivation, sucrose density gradient ultracentrifugation, and Sulfate-Cellulofine column chromatography are conducted. The antigen obtained from the manufacturing system was highly purified and its physico-chemical and immunological properties were comparable with those of antigen derived from mouse brains. Our system is very simple and could be easily scaled-up to allow vaccine production at a several thousand litre scale.

Non-clinical and phase I clinical trials of a Vero cell-derived inactivated Japanese encephalitis vaccine.

The safety and effectiveness of a Vero cell-derived inactivated Japanese encephalitis (JE) vaccine were compared with those of a current JE vaccine in non-clinical studies and a phase I clinical trial. The single-dose toxicity study showed no toxicity of either the current JE vaccine or the investigational Vero cell-derived JE vaccine. In a local irritation study, the degree of irritation caused by both vaccines was determined to be the same as that induced by normal saline. To investigate genotoxicity, a chromosomal aberration test was conducted and the results were negative. Both JE vaccines were administered to a group of 30 subjects who were seronegative (neutralizing antibody titer <10(1)) for JEV virus (Beijing-1 Strain). Each subject was subcutaneously inoculated twice at an interval of 1-4 weeks, followed by an additional booster inoculation 4-8 weeks later, and clinical reactions and serological responses were subsequently investigated. Adverse drug reactions of local reaction, headache and malaise were mild, occurring at a rate of 6.7 and 20.0% after administration of the Vero cell-derived JE vaccine and the current JE vaccine, respectively. The seroconversion rate after three doses of both JE vaccines was 100%, while the geometric mean titer for the Vero cell-derived and current JE vaccines was 10(2.35) and 10(2.03), respectively. These results suggest that the safety and effectiveness of the Vero cell-derived inactivated JE vaccine are equal to those of the currently available conventional vaccine in humans, and that the Vero cell-derived vaccine could be a useful second-generation JE vaccine.