Kanakatte Raviprakash

Inoculation of plasmids expressing the dengue-2 envelope gene elicit neutralizing antibodies in mice.

To develop a nucleic acid vaccine against dengue type-2 virus, the PreM and 92% of the envelope (E) genes were cloned into different eukaryotic plasmid expression vectors (pkCMVint Polyli and pVR1012). The resultant plasmid constructs (pD2ME and P1012D2ME) properly expressed the truncated E protein in vitro as evidenced by the expected protein size on SDS-PAGE and the ability of the protein to be recognized by monoclonal antibodies directed against conformational epitopes. Three-week-old BALB/c mice were given intradermal inoculations of each construct. Plasmid expression vectors without dengue genes were used as controls. One hundred percent of the mice that received the pD2ME and p1012D2ME constructs developed anti-dengue antibodies. These antibodies were shown to neutralize dengue type-2 virus in vitro. This is the first demonstration of the use of nucleic acid inoculation in the development of potential dengue virus. vaccines.

Immunogenicity of dengue virus type 1 DNA vaccines expressing truncated and full length envelope protein.

Recombinant plasmid DNA constructs expressing truncated or full-length dengue-1 envelope (E) with or without the pre-membrane (prM) were tested for immunogenicity in mice, as candidate dengue DNA vaccines. Two plasmids, one expressing the N-terminal 80% E and the other expressing prM and full length E were immunogenic in intradermally inoculated mice. The vaccinated mice produced dengue-1 specific antibodies that were both neutralizing and long lasting. Data suggested that the plasmid expressing prM and full length E produced virus like particles in transfected cells, and is probably a better immunogen compared to that expressing 80% E.

A dengue virus serotype-1 DNA vaccine induces virus neutralizing antibodies and provides protection from viral challenge in Aotus monkeys.

A DNA vaccine that expresses the premembrane/membrane (prM) and envelope (E) genes of dengue virus serotype-1 was tested for immunogenicity and protection against dengue-1 virus challenge in Aotus nancymae monkeys. The vaccine, in 1 mg doses, was administered intradermally (i.d.) to three monkeys and intramuscularly (i.m.) to three others. For controls, a 1 mg dose of vector DNA was administered i.d. to two monkeys and i.m. to one. All animals were primed and then boosted at one and five months post priming. Sera were collected monthly and analyzed for dengue-1 antibodies by enzyme linked immunosorbent assay (ELISA) and plaque reduction neutralization test (PRNT). Dengue-1 antibodies were detectable in the sera from i.d. and i.m. vaccine inoculated animals one month after the first boost and peaked one month after the second boost. The antibody levels from sera of animals that received the vaccine via the i.d. route were twice those from sera of animals that received the vaccine via the i.m. route. Six months after the second boost all inoculated and two naive monkeys were challenged with 1.25x10(4) plaque forming units (PFU) of dengue-1 virus. Two vaccine immunized animals were protected from viremia while the others showed a reduction in viremia. The mean days of viremia were 1 and 1.3 for the animals that were immunized with the vaccine via the i.d. or i.m. route, respectively vs 4 and 2 mean days of viremia in the animals inoculated with control DNA. Naive animals were viremic for an average of 4 days. All of the three control monkeys that received control DNA inoculum by either the i.d. or i.m. route had an intermittent viremia pattern with one or more negative days interspersed between the positive days. This pattern was not observed in any of the vaccine recipients or the naïve control monkeys. These results demonstrate that DNA immunization is a promising approach for the development of dengue vaccines and that A. nancymae monkeys are suitable for dengue vaccine trials.

Evaluation of a prototype dengue-1 DNA vaccine in a Phase 1 clinical trial.

Candidate dengue DNA vaccine constructs for each dengue serotype were developed by incorporating pre-membrane and envelope genes into a plasmid vector. A Phase 1 clinical trial was performed using the dengue virus serotype-1 (DENV-1) vaccine construct (D1ME(100)). The study was an open-label, dose-escalation, safety and immunogenicity trial involving 22 healthy flavivirus-naïve adults assigned to one of two groups. Each group received three intramuscular injections (0, 1, and 5 months) of either a high dose (5.0mg, n=12) or a low dose (1.0mg, n=10) DNA vaccine using the needle-free Biojector(®) 2000. The most commonly reported solicited signs and symptoms were local mild pain or tenderness (10/22, 45%), local mild swelling (6/22, 27%), muscle pain (6/22, 27%) and fatigue (6/22, 27%). Five subjects (41.6%) in the high dose group and none in the low dose group developed detectable anti-dengue neutralizing antibodies. T-cell IFN gamma responses were detected in 50% (4/8) and 83.3% (10/12) of subjects in the low and high dose groups, respectively. The safety profile of the DENV-1 DNA vaccine is acceptable at both doses administered in the study. These results demonstrate a favorable reactogenicity and safety profile of the first in human evaluation of a DENV-1 DNA vaccine.

Needle-free Biojector injection of a dengue virus type 1 DNA vaccine with human immunostimulatory sequences and the GM-CSF gene increases immunogenicity and protection from virus challenge in Aotus monkeys

A dengue-1 DNA vaccine containing sequences encoding premembrane and envelope proteins (DIME) was previously shown to elicit virus neutralizing antibodies in rhesus and Aotus monkeys, and the primates were partially protected from viremia upon challenge. To increase the neutralizing antibody levels and subsequent protection from virus challenge, four strategies were evaluated: (a) coimmunization with a plasmid expressing Aotus GM-CSF gene; (b) coimmunization with a plasmid containing human immunostimulatory sequences (ISS); (c) coimmunization with both the GM-CSF gene and ISS; and (d) delivery of vaccine using the needle-free Biojector system. Vaccination with the mixed formulation containing DIME, GM-CSF gene, and ISS, by either needle injection or Biojector, led to neutralizing antibody titers that were stable for up to 6 months after vaccination. Furthermore, 6 of 7 monkeys (85%), and 7 of 8 monkeys (87%) receiving this formulation were completely protected from viremia when challenged 1 and 6 months after vaccination, respectively. This is a significant improvement compared to our previous study in which one of three monkeys (33%) receiving just the DIME vaccine was completely protected from viremia at 6 months after immunization.

A Tetravalent Dengue Vaccine Based on a Complex Adenovirus Vector Provides Significant Protection in Rhesus Monkeys against All Four Serotypes of Dengue Virus

ABSTRACT Nearly a third of the human population is at risk of infection with the four serotypes of dengue viruses, and it is estimated that more than 100 million infections occur each year. A licensed vaccine for dengue viruses has become a global health priority. A major challenge to developing a dengue vaccine is the necessity to produce fairly uniform protective immune responses to all four dengue virus serotypes. We have developed two bivalent dengue virus vaccines, using a complex adenovirus vector, by incorporating the genes expressing premembrane (prM) and envelope (E) proteins of dengue virus types 1 and 2 (dengue-1 and -2, respectively) (CAdVax-Den12) or dengue-3 and -4 (CAdVax-Den34). Rhesus macaques were vaccinated by intramuscular inoculation of a tetravalent dengue vaccine formulated by combining the two bivalent vaccine constructs. Vaccinated animals produced high-titer antibodies that neutralized all four serotypes of dengue viruses in vitro. The ability of the vaccine to induce rapid, as well as sustained, protective immune responses was examined with two separate live-virus challenges administered at 4 and 24 weeks after the final vaccination. For both of these virus challenge studies, significant protection from viremia was demonstrated for all four dengue virus serotypes in vaccinated animals. Viremia from dengue-1 and dengue-3 challenges was completely blocked, whereas viremia from dengue-2 and dengue-4 was significantly reduced, as well as delayed, compared to that of control-vaccinated animals. These results demonstrate that the tetravalent dengue vaccine formulation provides significant protection in rhesus macaques against challenge with all four dengue virus serotypes.

Dengue 2 PreM-E/LAMP chimera targeted to the MHC class II compartment elicits long-lasting neutralizing antibodies.

A dengue 2 plasmid DNA vaccine (pD2) expressing the pre-membrane and envelope proteins (preM-E) was modified by replacing the dengue transmembrane and cytoplasmic sequences with those of the mouse lysosome-associated membrane protein (pD2/LAMP). Immunofluorescence and confocal microscopy of human 293, NIH 3T3, and macrophage IC21 cell lines transfected with pD2/LAMP showed that the preM-E/LAMP protein chimera was present in vesicles containing endogenous LAMP and major histocompatability complex class II (MHC II), in contrast to the non-vesicular localization of native preM-E protein lacking the LAMP targeting sequence. Mice immunized with pD2 showed an antigen-specific immunoglobulin response but the neutralizing antibodies titers (plaque reduction neutralization test, PRNT(50)) elicited by the native protein were minimal. In contrast, vaccination with pD2/LAMP resulted in PRNT(50) of 270, 320 and 160 at approximately 1, 3 and 8 months after two immunizations with 50 microg DNA, and approached 100% neutralization at 1:20 dilution. Additional immunization with pD2/LAMP, after 8 months, increased the neutralizing antibody titers to >640. Comparable neutralizing antibody responses were induced by two vector backbones, pVR1012 and pVax-1, at 5 and 50 microg of DNA. The neutralizing responses to the pD2/LAMP chimera were greatly superior to those elicited by pD2 in all conditions. These results underscore the importance of MHC class II presentation of DNA-encoded dengue-virus envelope protein for production of neutralizing antibodies.

A Heterologous DNA Prime-Venezuelan Equine Encephalitis Virus Replicon Particle Boost Dengue Vaccine Regimen Affords Complete Protection from Virus Challenge in Cynomolgus Macaques

ABSTRACT A candidate vaccine (D1ME-VRP) expressing dengue virus type 1 premembrane and envelope proteins in a Venezuelan equine encephalitis (VEE) virus replicon particle (VRP) system was constructed and tested in conjunction with a plasmid DNA vaccine (D1ME-DNA) expressing identical dengue virus sequences. Cynomolgus macaques were vaccinated with three doses of DNA (DDD), three doses of VRP (VVV group), or a heterologous DNA prime-VRP boost regimen (DDV) using two doses of DNA vaccine and a third dose of VRP vaccine. Four weeks after the final immunization, the DDV group produced the highest dengue virus type 1-specific immunoglobulin G antibody responses and virus-neutralizing antibody titers. Moderate T-cell responses were demonstrated only in DDD- and DDV-vaccinated animals. When vaccinated animals were challenged with live virus, all vaccination regimens showed significant protection from viremia. DDV-immunized animals were completely protected from viremia (mean time of viremia = 0 days), whereas DDD- and VVV-vaccinated animals had mean times of viremia of 0.66 and 0.75 day, respectively, compared to 6.33 days for the control group of animals.

Two Complex, Adenovirus-Based Vaccines That Together Induce Immune Responses to All Four Dengue Virus Serotypes

ABSTRACT Dengue virus infections can cause hemorrhagic fever, shock, encephalitis, and even death. Worldwide, approximately 2.5 billion people live in dengue-infested regions with about 100 million new cases each year, although many of these infections are believed to be silent. There are four antigenically distinct serotypes of dengue virus; thus, immunity from one serotype will not cross-protect from infection with the other three. The difficulties that hamper vaccine development include requirements of the natural conformation of the envelope glycoprotein to induce neutralizing immune responses and the necessity of presenting antigens of all four serotypes. Currently, the only way to meet these requirements is to use a mixture of four serotypes of live attenuated dengue viruses, but safety remains a major problem. In this study, we have developed the basis for a tetravalent dengue vaccine using a novel complex adenovirus platform that is capable of expressing multiple antigens de novo. This dengue vaccine is constructed as a pair of vectors that each expresses the premembrane and envelope genes of two different dengue virus serotypes. Upon vaccination, the vaccine expressed high levels of the dengue virus antigens in cells to mimic a natural infection and induced both humoral and cellular immune responses against multiple serotypes of dengue virus in an animal model. Further analyses show the humoral responses were indeed neutralizing against all four serotypes. Our studies demonstrate the concept of mimicking infections to induce immune responses by synthesizing dengue virus membrane antigens de novo and the feasibility of developing an effective tetravalent dengue vaccine by vector-mediated expression of glycoproteins of the four serotypes.

Human polyclonal immunoglobulin G from transchromosomic bovines inhibits MERS-CoV in vivo

Anti–MERS-CoV human IgG produced from transchromosomic bovines neutralizes MERS-CoV in vitro and in vivo. Emerging therapeutics The ability to treat emerging infections, such as the Middle East respiratory syndrome coronavirus (MERS-CoV), has been limited by the turnaround time of developing new therapeutics. Now, Luke et al. report that transchromosomal bovines can rapidly produce large quantities of fully human polyclonal IgG antibodies to MERS-CoV after vaccination. These antibodies could neutralize MERS-CoV both in vitro and clear infection in mice in vivo. Human testing will confirm whether passive immunization with these antibodies can safely and effectively treat infection in infected individuals. As of 13 November 2015, 1618 laboratory-confirmed human cases of Middle East respiratory syndrome coronavirus (MERS-CoV) infection, including 579 deaths, had been reported to the World Health Organization. No specific preventive or therapeutic agent of proven value against MERS-CoV is currently available. Public Health England and the International Severe Acute Respiratory and Emerging Infection Consortium identified passive immunotherapy with neutralizing antibodies as a treatment approach that warrants priority study. Two experimental MERS-CoV vaccines were used to vaccinate two groups of transchromosomic (Tc) bovines that were genetically modified to produce large quantities of fully human polyclonal immunoglobulin G (IgG) antibodies. Vaccination with a clade A γ-irradiated whole killed virion vaccine (Jordan strain) or a clade B spike protein nanoparticle vaccine (Al-Hasa strain) resulted in Tc bovine sera with high enzyme-linked immunosorbent assay (ELISA) and neutralizing antibody titers in vitro. Two purified Tc bovine human IgG immunoglobulins (Tc hIgG), SAB-300 (produced after Jordan strain vaccination) and SAB-301 (produced after Al-Hasa strain vaccination), also had high ELISA and neutralizing antibody titers without antibody-dependent enhancement in vitro. SAB-301 was selected for in vivo and preclinical studies. Administration of single doses of SAB-301 12 hours before or 24 and 48 hours after MERS-CoV infection (Erasmus Medical Center 2012 strain) of Ad5-hDPP4 receptor–transduced mice rapidly resulted in viral lung titers near or below the limit of detection. Tc bovines, combined with the ability to quickly produce Tc hIgG and develop in vitro assays and animal model(s), potentially offer a platform to rapidly produce a therapeutic to prevent and/or treat MERS-CoV infection and/or other emerging infectious diseases.