Status: BLA filing originally expected in 2007

Organizations involved:

Acambis PLC – Manuf.; R&D; Tech.; Parent

Sanofi Pasteur S.A. – World mark.; Manuf. other

Baxter Healthcare Corp. – Tech.

Bharat Biotech Intl. Ltd. – Former

St. Louis University – R&D; Tech.

Cross ref.: See the entry for Yellow Fever Virus Vaccine, Live (YF-VAX; #567), used as the vector forming the backbone or basic structural component of this chimeric virus vaccine; and the entry for Japanese Encephalitis Vaccine/Intercell (#490), which uses the same Japanese encephalitis virus SA14-14-2 strain. See also the non-recombinant JE vaccines in the Vaccine Products section, including JE-VAX, currentlyl marketed by Sanofi Pasteur, but is no longer marketed and will essentially be replaced by Chimerivax-JE.

Description: ChimeriVax-JE is a lyophilized (freeze-dried) formulation of a recombinant, attenuated, single-dose, live virus vaccine containing chimeric virus consisting of structural genes (prM and E) from Japanese encephalitis virus (JE) strain SA14-14-2 inserted/substituted into an attenuated (nonpathogenic) yellow fever virus strain 17D vector (carrier), with the resulting chimeric virus cultured in Vero fetal rhesus monkey kidney cells. The resulting chimeric virus has the envelope of JE virus, including neutralizing epitopes and determinants for host cell tropism, and the capsid and nonstructural genes of yellow fever virus 17D responsible for replication. This chimeric virus is prepared by replacing the genes encoding two structural capsid proteins (prM and E) of yellow fever virus (YF) 17D vaccine strain with the corresponding genes of the attenuated JE vaccine strain SA14-14-2 . Note, the yellow fever virus 17D strain, itself, is used as a live vaccine; see the entry for Yellow Fever Virus Vaccine, Live or YF-VAX). Since the prM and E proteins contain antigens confer protective humoral and cellular immunity, the immune response to vaccination is directed principally at Japanese encephalitis virus. The prM and E proteins contain critical antigens conferring protective humoral and cellular immunity against JE.

Safety of the chimeric vaccine is ensured by deriving all genes from an attenuated vaccine virus strains. The Japanese encephalitis virus (JE) prM and E genes are from JE strain SA14-14-2, a live, attenuated JE vaccine strain widely used in China (PRC). The remaining genes of the chimeric virus, including the capsid gene and all of the nonstructural (NS) genes responsible for intracellular replication, are derived from YF 17D used for 60 years with an excellent record of safety and effectiveness (see the YF-VAX entry).

Nomenclature: Japanese encephalitis vaccine, rDNA/Acambis [BIO]; ChimeriVax-JE [TR]; YF/JE SA14-14-2 [SY]; Japanese encephalitis virus vaccine, yellow fever virus YF 17D vector, recombinant [SY]

Biological.: ChimeriVax technology from Acambis utilizes yellow fever virus (YF) 17D vaccine strain capsid and nonstructural genes, i.e., structural and replication-related components, to deliver the viral envelope gene(s) of other flaviviruses as live-attenuated chimeric viruses. ChimeriVax-JE is a live, attenuated recombinant virus prepared by replacing the genes encoding two structural proteins (prM and E) of yellow fever 17D virus, used as the vector, with the corresponding genes of an attenuated strain of Japanese encephalitis virus (JE), SA14-14-2. ChimeriVax-JE was constructed by insertion of the prM-E genes from the attenuated JE virus SA14-14-2 vaccine strain into a full-length cDNA clone of YF 17D virus. Passage in fetal rhesus lung (FRhL) cells led to the emergence of a small-plaque virus containing a single MetLys amino acid mutation at E279, reverting this residue from the SA14-14-2 to the wild-type amino acid. The E279 mutation is located in a beta-sheet in the hinge region of the E protein that is responsible for a pH-dependent conformational change during virus penetration from the endosome into the cytoplasm of the infected cell.

Construction of the YF-JE chimera was described by Chambers et al., “Yellow fever/Japanese encephalitis chimeric viruses: construction and biological properties” (J. Virol., 1999; 73:3095–3101). The entire genome of YF 17D (17D-204 substrain, from ATCC) was cloned into two plasmids. This provided smaller plasmids that were more stable to manipulate the YF sequences and facilitated replacement of the prM and E genes of the flavivirus target vaccine. Cloning sites were engineered to permit replacement of the entire pre-M and E coding sequences of JE SA14-14-2 with the corresponding sequences of YF 17D. Sites for posttranslational cleavage of the capsid and pre-M proteins and of the E and NS1 proteins were preserved. Restriction sites were incorporated in both the YF and JE sequences for in vitro ligation of full-length cDNA. Transcription to mRNA was performed. Chimeric virus was prepared by transfecting full-length RNA transcripts into diploid fetal rhesus lung (FRhL) cells by electroporation and passaging the progeny virus in FRhL cells. Passage 5 (FRhL5) is the intended passage level for the vaccine to be administered to humans. Chimeric virus has been shown to be stable after 18 sequential passages in culture.

Fully processed mature flavivirus virions contain three structural proteins, envelope (E), capsid (C), and membrane (M), and seven non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). After binding of virions to host cell receptors, the E protein undergoes an irreversible conformational change upon exposure to the acidic pH of endosomes, causing fusion between the envelope bilayers of the virions and endocytic vesicles, thus releasing the viral genome into the host cytosol. The M protein interacts with amino acids 200-327 of the E protein. This interaction protects the E protein from irreversible conformational changes caused by maturation in the acidic vesicles of the exocytic pathway. The M protein is cleaved from its precursor protein (prM) after the consensus sequence R-X-R/K-R (X is variable), and incorporated into the virus lipid envelope together with the E protein.

The live Chimerivax-JE exhibits restricted replication in vivo, producing only a low-level viremia following peripheral inoculation. This reduces the likelihood that hematophagous insects, e.g., mosquitos, could become infected by feeding on a vaccinated host, and ChimeriVax-JE virus has been shown to be restricted in its ability to infect and replicate in mosquito vectors. The low viremia caused by ChimeriVax-JE in primates and poor infectivity for mosquitoes are safeguards against secondary spread of the vaccine virus.

Protection against JE virus infection in vaccinated individuals is mediated principally by preformed JE virus-neutralizing antibodies. Cross-protection between heterologous members of the JE antigenic complex has been repeatedly demonstrated, indicating that the vaccine should retain efficacy against diverse JE virus strains encountered worldwide.

In preclinical studies, Chimerivax-JE was not neurovirulent at doses up to 6 log PFU in intracerebrally inoculated mice and in rhesus monkeys given doses of 7 log PFU intracerebrally. Mice inoculated with a single ≥103 PFU dose were protected from intraperitoneal challenge with wild type JE virus. Vaccine strain viremia in monkeys lasted for two days and was similar to that induced by YF 17D. No monkeys showed any signs of illness and all developed high titers of JE virus neutralizing antibodies. The vaccine protected primates against intracerebral and intranasal challenges with wild-type JE virus.

The YF virus vector is the same as used in the JE-VAX yellow fever vaccine, which is widely considered “one of the safest live virus vaccines ever developed.” These properties are expected to apply to other YF 17D vaccine constructs.

Companies.: Chimerivax-JE has been commercially developed Acambis PLC, and is manufactured at company facilities in Canton, MA. The Berna Products, Corp. subsidiary of Acambis will market the vaccine in the U.S. and certain other territories.

In late 1998, Pasteur Merieux Connaught (PMC), now Sanofi Pasteur, purchased from OraVax (now Acambis) the option to negotiate an agreement to license ChimeriVax-JE in all territories except Korea, where OraVax was in separate negotiations. No commercial licensing has apparently resulted from this.

In Feb. 2007, with positive results from the pivotal Phase III trial (see Trials section below), Sanofi Pasteur licensed exclusive worldwide marketing, distribution and certain manufacturing rights, excluding India and the Indian subcontinent and the U.S., for which Sanofi Pasteur received a licensing option. Sanofi Pasteur plans to introduce the vaccine in Europe and throughout the Asia Pacific region, with particular focus on the large endemic countries, including Thailand and China. Acambis will receive royalties on sales and payment for the supply of bulk manufactured ChimeriVax-JE product, and will receive upfront and milestone payments of up to €30 million following approvals of ChimeriVax-JE in key endemic countries and in the European Union.

On Nov. 8, 2005, Acambis concluded an agreement with Bharat Biotech International Ltd. for the manufacture and marketing of ChimeriVax-JE in India. Bharat Biotech received exclusive marketing rights in India and neighboring countries. Bulk vaccine would be manufactured at Acambis’ Canton, MA, facilities. Bharat Biotech would be responsible for end-stage fill/finish processing of ChimeriVax-JE at its Hyderabad-based manufacturing plant, the largest in the Asia-Pacific region. Bharat Biotech would market the vaccine using its own established sales force and distribution network serving India and surrounding countries. In parallel with the Phase III trials in Australia and the U.S., Acambis had been conducting clinical trials in India to support approval of ChimeriVax-JE for populations where the disease is endemic. Bharat Biotech has the capacity to manufacture ~1 million doses/month, but initial/launch plans call for manufacture of only about 1 million doses/year.

In March 2008, Acambis extended its agreement with Sanofi Pasteur. to include India and the Indian subcontinent. Acambis and Bharat Biotech had mutually agreed to cancel their prior Indian marketing agreement. As with its preexisting agreement, Acambis will supply bulk ChimeriVax-JE vaccine to Sanofi Pasteur from its Canton, MA facility

In 2003, Acambis decided to bring commercial scale manufacture of ChimeriVax-JE in-house and to finalize scale-up of its manufacturing process to optimize a stable, freeze-dried formulation prior to initiating Phase III testing in 2005. A bridging trial was initiated to confirm bioequivalence, i.e., that the new material manufactured in Canton, OH, facilities has a clinical profile substantially similar to that of vaccine used in previous trials.

Status: Acambis originally planned to file a BLA for FDA approval for use in for traveller's and JE endemic populations in the first half of 2007. This has not happened yet. Acambis' clinical studies have concentrated on use in travelers. This U.S. filing will presumably be followed by applications in Europe and other countries worldwide.

Tech. transfer: In fall 1997, OraVax acquired an exclusive license from St. Louis University for the chimeric vector vaccine (Chimerivax) technology used by OraVax with its series of ChimeriVax vaccines against flaviruses, including Japanese encephalitis, dengue and hepatitis C virus. Chimerivax technology developed by Dr. T. Chambers and workers, St. Louis Univ., involves constructing a recombinant virus using the live attenuated Japanese encephalitis virus strain 17D, the same virus used in Japanese Encephalitis Virus Vaccine Inactivated JE-VAX (Japanese Encephalitis Virus Vaccine Inactivated from Sanofi Pasteur) as the vector, with genes for immunogenic components from other flaviviruses, e.g., JE, exchanged for corresponding YF genes. This JE 17D virus vector adopted for Chimerivax vaccines contains its own genes required for replication, with genes exchanges/swapped for expression of viral coat antigens of the target virus.

U.S. 6,962,708 and 6,696,281, “Chimeric flavivirus vaccines,” co-assigned to Acambis, Inc. and St. Louis University has an exemplary claim (no. 1): “A chimeric live, infectious, attenuated virus, comprising: a yellow fever virus in which the nucleotide sequence encoding a prM-E protein is either deleted, truncated, or mutated so that functional yellow fever virus prM-E protein is not expressed, and integrated into the genome of said yellow fever virus, a nucleotide sequence encoding a prM-E protein of a second, different flavivirus, to that said prM-E protein of said second flavivirus is expressed, wherein the capsid protein of said chimeric virus is from yellow fever virus.”

Acambis has licensed Vero cell culture technology from Baxter, and will make royalty payments to Baxter.

Trials: A Phase I trial and a Phase II ‘challenge’ trial were completed in 2001. The Phase I trial demonstrated proof-of-principle for ChimeriVax technology. In the challenge trial, subjects vaccinated with ChimeriVax-JE exhibited an immune response with long-term memory and a rapid rise in protective antibodies after exposure to live JE virus, supporting the vaccine’s potential as a single-dose vaccine for travellers to JE-endemic areas. Of the 197 subjects who provided pre- and post-vaccination blood samples for analysis, 190 (96%) seroconverted, developing JE-neutralizing antibody titers 28 days after receiving a single dose of ChimeriVax-JE. Neutralizing antibody levels remained high at both six and 12 months after a single inoculation. There was no interference with chimeric vaccination by prior immunity to YF, but a slight interference was noted in persons given YF 17D vaccine 30 days after ChimeriVax-JE.

Results from Phase II studies completed in 2002 were reported in the Oct. 2003 edition of the Journal of Infectious Diseases (vol. 188, no. 8, p. 1213-30). This randomized, double-blind placebo- and yellow fever vaccine (YF-Vax)-controlled outpatient trial was conducted in the U.S., with 99 healthy adults randomized to receive two intramuscular injections (30 days apart) of one of five dose levels of ChimeriVax-JE (5.8, 4.8, 3.8, 2.8 or 1.8 log10 plaque-forming units [PFU]) or a single dose of ChimeriVax-JE (4.8 log10 PFU) preceding or following placebo or a standard dose of yellow fever vaccine (YF-Vax). ChimeriVax-JE was well tolerated, with no differences in adverse events between treatment groups. Viremias resulting from administration of ChimeriVax-JE (and YF-VAX) were of short duration and low titer. Among 87 subjects administered graded doses (1.8-5.8 log10) of ChimeriVax-JE, 82 (94%) developed JE virus neutralizing antibodies. A second dose administered 30 days later had no booster effect. The seroconversion rates and mean titers of neutralizing antibodies were statistically the same when comparing one injection to two injections (at all dose levels) and when comparing the highest (5.8 log10 PFU) with the lowest (1.8 log10 PFU) dose levels administered. The seroconversion rates were similar across all dose levels. The lowest dose was ~1,000 times lower than the highest dose used previously. Previous inoculation with YF-Vax did not interfere with ChimeriVax-JE, but there was a suggestion (not statistically significant) that ChimeriVax-JE interfered with YF-VAX administered 30 days later. Another study explored immunological memory both in subjects who had received ChimeriVax-JE 9 months before and in ChimeriVax-JE-naive subjects challenged with JE-VAX. Anamnestic responses were observed in preimmune individuals. ChimeriVax-JE appeared to be a safe vaccine that provides protective levels of neutralizing antibody after a single dose. With positive Phase II results in hand, Acambis then concentrated on finalizing the formulation and scale-up for commercial manufacture.

In Aug. 2005, a bridging study using the new stable, freeze-dried formulation manufactured at commercial-scale at the Canton, MA, facility showed a 96% seroconversion to JE virus-neutralizing antibodies after a single-dose of ChimeriVax-JE, results consistent with those of previous Phase I and II studies using vaccine manufactured elsewhere and/or using a different process.

In Nov. 2005, Acambis initiated large pivotal Australian and U.S. Phase III trials comparing ChimeriVax-JE to JE-Vax (inactivated virus vaccine from Sanofi Pasteur; see related entry). The two trials are enrolling over 2,800 healthy adult subjects have been designed to provide comprehensive safety data and test the non-inferiority of ChimeriVax-JE to JE-VAX by statistical comparison of immunogenicity (i.e., induction of virus-neutralizing antibodies is used as a surrogate marker for clinical prophylactic efficacy). The efficacy study portion, enrolling 800 adults, will also test clinical consistency of three commercial-scale batches of ChimeriVax-JE manufactured at Acambis’ Canton, MA facility. The remaining 2,000 subjects are included in the safety study.

In Jan. 2007, Acambis initiated a single-dose pediatric trial in India; and also reported, “To date, ChimeriVax-JE has already been tested in approximately 2,400 adult volunteers.”

In March 2007, Acambis reported that “ChimeriVaxTM-JE, has met and exceeded the primary immunogenicity endpoint in a pivotal Phase 3 efficacy trial.” In this randomised, double-blind, multi-center Phase III study, 820 adult subjects were vaccinated at a 1:1 ratio with either single-dose ChimeriVax-JE or JE-VAX, the licensed three-dose JE vaccine. The trial compared immunogenicity 30 days after immunization, with subjects receiving either two doses of placebo (saline) followed by one dose of ChimeriVax-JE or the full three-dose schedule of JE-VAX. The primary efficacy endpoint, seroconversion rates based on neutralising antibodies against the homologous JE virus, was met, showing the non-inferiority of ChimeriVax-JE to JE-VAX. Of the subjects vaccinated with ChimeriVax-JE, 99.1% seroconverted vs. 74.8% in the JE-VAX group. The efficacy of ChimeriVax-JE statistically superior to JE-VAX (p <0.05). ChimeriVax-JE elicited a rapid immune response, with 93.6% of those vaccinated with ChimeriVax-JE generating neutralizing antibodies 14 days after vaccination. There were no vaccine-related serious adverse events observed during the 60-day treatment observation period. The overall incidence of adverse events following vaccination was slightly lower in the ChimeriVax-JE group than in the JE-VAX group, and the incidence of local injection site reactions in the ChimeriVax-JE group was significantly lower than in the JE-VAX group. Preliminary results from this trial had been reported in Oct. 2006.

Acambis is collaborating with the World Health Organization for pediatric trials of ChimeriVax-JE in endemic countries.

Medical: ChimeriVax-JE offers potential advantages over existing JE vaccines, including requiring only a single dose, production in an acceptable cell culture system, and lower costs of manufacture.

Disease: See the Japanese Encephalitis Virus Vaccine (JE-Vax) entry in the Vaccine Products section. In India, JE has been resulting in ~15,000 deaths/year, despite the availability of vaccines for the past 60 years.

Market: The introduction of a single-dose vaccine, such as Chimerivax-JE, may transform the use of vaccines against JE by making it simpler, faster, easier and cheaper for healthcare providers to administer, particularly in regions where achieving compliance to multi-dose regimens can be difficult. Current JE vaccines, e.g., JE-VAX, are administered in multiple doses. Human vaccination remains the only reliable tool to control JE. No antiviral drugs are available and mosquito control has not proven successful. Particularly, in the U.S. and developed countries, the use of inactivated mouse brain-cultured vaccines, e.g., JE-VAX, has been hampered by reports of neurological reactions and various side effects after vaccination, their short-term protection, and limited production capacity. A significant numbers of cases of hypersensitivity reactions have been reported and vaccinees are advised to stay in areas with medical resources for 10 days after receiving the vaccine.

Although JE vaccine is best known as a traveler’s vaccine administered to adults in developed/affluent countries, children will likely be the primary target population for the vaccine in endemic regions, particularly with a more effective and safer vaccine.

The current JE vaccine available in India is administered in three doses costing Rs 150 (~$3.40). Bharat Biotech is expected to price its vaccine comparably.