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Feature Articles : Nov 1, 2008 ( )
Vaccine Development Aided by New Techniques
Field Revitalized by In-Depth Understanding of Infectious Diseases and Immunology!--h2>
The cyclical fortunes that have characterized the vaccines business for decades have swung decidedly positive, with no indication that they will slip again any time soon.
Today, vaccine development and manufacturing, more than perhaps any other area of biotechnology, are characterized by innovation, even daring. Developers tackle not just the easy targets like seasonal influenza but the most intractable communicable and noncommunicable diseases as well.
The industry has received several shots in the arm from the emergence of potentially pandemic viral infections, the threat of bioterrorism, and the promise of vaccination against noninfectious diseases such as cancer and heart disease.
“For years vaccines were considered a competitive, high-risk business characterized by low prices and high-liability exposure,” says Mike Kowolenko, Ph.D., svp for biotechnology at Wyeth. “Advances in our understanding of infectious diseases and immunology have revitalized vaccine development. Today’s vaccines are, therefore, more cost-effective and scientifically driven.”
Vaccine manufacturing has tracked development and manufacturing trends in biotech but has lagged by several years. Today’s developers increasingly seek to upgrade their production and expression systems, in favor of new cell culture technologies. Vaccine makers are beginning to adopt newer analytic techniques as well as more formal quality practices and methodologies like process analytic technology (PAT) and quality by design.
“Biotech was a black box back in the seventies,” notes Dr. Kowolenko. “It only became less so once we gained knowledge and understanding of those tools that influence process outcomes. Vaccine makers are now beginning to apply lessons learned from biotech.”
Vaccine makers must continuously innovate through manufacturing efficiencies, by concentrating on difficult targets, or by adding significant value to existing products.
For example Wyeth is looking to improve on its Prevnar pneumococcus vaccine, which is heptavalent, by developing a 13-valent product. “To do so requires the ability to control polysaccharide expression in bacteria, and to purify and conjugate those antigens,” Dr. Kowolenko reports.
In vaccines, the entry of even two or three competitors quickly relegates products to commodity status. This is what has happened, cyclically, to manufacturers of seasonal flu vaccine.
“The low-hanging fruit in vaccinology has already been harvested,” says Vijay Samant, CEO of Vical, which focuses exclusively on DNA vaccines. “If you’re going to be a player, pick a target nobody is working on and either get a head start, come up with a high-efficiency process, or figure out a way to provide long-term immunity.”
Vical has a Phase II DNA-based cytomegalovirus vaccine for treating bone marrow transplant patients and is working on products to combat SARS, Ebola, West Nile, herpes, and human immunodeficiency viruses, in addition to programs on dengue, angiogenesis, and melanoma. It is also developing a vaccine to prevent hematopoietic necrosis virus, a pathogen that spreads from wild salmon, in which it is harmless, to farm-raised salmon, which it kills.
“Vaccines made outside the human body are limited to generating antibody-mediated responses,” Samant notes. “The same is true for vaccines produced in cell culture. The only thing that comes close to generating the response from DNA vaccines are live attenuated vaccines.”
Vical manufactures its vaccines through fermentation of E. coli in 1,000 to 2,000 liter bioreactors. Fermentation is more productive and easier to standardize, validate, and scale, and presents fewer matrix impurities than cell culture. Also, with DNA vaccines, processes tend to be of the platform variety, suitable for almost any vaccine product.
Manufacturing DNA vaccines in weeks rather than months may provide a significant advantage when dealing with emerging infectious diseases such as pandemic influenza. “The speed at which we can make the vaccine is, in part, due to the fact that we do not need to handle the pathogen itself,” explains Samant.
Vical recently announced preliminary clinical trial data suggesting that its DNA vaccines safely induce significant human immune responses against H5N1 pandemic influenza.
The 100-person Phase I study demonstrated that the company’s Vaxfectin® adjuvant-formulated vaccine produced potentially protective antibodies, as measured by hemagglutination inhibition titers, similar to those of conventional vaccines. The data also suggests that the vaccine induces immunity to strains of H5N1 influenza not matching that of the vaccine. Cross-strain protection is key for utilizing vaccine stockpiled against rapidly-mutating viruses.
Alternative Delivery Mechanisms
DNA vaccines lend themselves to several novel gene-delivery systems including nonpathogenic viral carriers. In July, GeoVax announced it had engaged the services of Vivalis, to adapt the French company’s EBx® cell lines to produce modified vaccinia Ankara (MVA), a smallpox virus component of GeoVax’ DNA HIV vaccine.
MVA is an attenuated virus created by passaging 500 times in chicken cells. The result is a virus that grows easily in chicken cells, but cannot replicate within mammalian cells. MVA is programmed with genes coding for HIV proteins, which are then expressed in the cytoplasms of infected cells. Like other DNA-based vaccines, GeoVax’s early-stage clinical product induces both antibody and T-cell immunity.
Previously, GeoVax expressed MVA in cultured, attachment-dependent chicken cells in small, multiple vessels. Vivalis’ avian stem cell-derived EBx lines produce suspension cultures, allowing the GeoVax MVA component to be grown and scaled to appropriate volumes in bioreactors.
In addition to carrying genes for expressing three of the major antigenic HIV proteins—GAG (an internal structural protein), POL (polymerase), and env (envelope)—MVA serves as a kind of adjuvant and immunizes against smallpox in the bargain. According to Harriet Robinson, Ph.D., svp of R&D at GeoVax, the vaccine can be used as a therapeutic as well as a preventive measure.
“Aside from protective immunity, the vaccine might also serve to control viral load in HIV without the need to take antiviral drugs. Administered early enough, it might even prevent immune system damage.”
The success of Merck’s Gardasil HPV can only be viewed as encouraging for developers of vaccines based on virus-like particles (VLPs). VLPs are recombinant structures that mimic the size and shape of a virus, but lack genetic material and, therefore, the ability to replicate. Their ability to present antigens in the same configuration as viruses is believed to be the source of the immune response VLPs induce.
In August, Novavax reported favorable results from a Phase I/IIa trial of its pandemic influenza VLP vaccine candidate. The unadjuvanted vaccine targets an Indonesian strain of avian flu with fatality rates above 80%. In this study, the vaccine induced dose-dependent levels of strong neutralizing antibodies.
Disposable Processing to the Rescue
While Merck produces Gardasil in yeast, Novavax relies on baculovirus-transfected insect cell cultures. Novavax has teamed with GE Healthcare to develop an entirely disposable process for its VLP vaccine, claiming yields that are seven to ten times higher than for traditional egg-based or mammalian cell culture manufacturing.
Because baculovirus does not infect humans, manufacturing need not occur under strict biocontainment conditions. Plus, the flexibility of disposables permits rapid commissioning of manufacturing space, at a fraction of the cost for egg- or cell culture-based processes.
The Novavax manufacturing facility was constructed for less than $20 million. Compare that to the cost of a typical vaccine plant using multiple-use equipment, which is in the $200 million to $400 million range. According to Novavax, its VLP vaccines can reach clinics within three months of identifying a pandemic strain. Egg-based products take about six months.
Novavax operates a prototype facility in Rockville, which when fully operational, will feature a 1,000 L process capable of producing one million doses per week. This facility was built for less than $6 million, including facility renovation and equipment.
“The use of disposables allows us to shift 70% of costs to variable cost,” says Rahul Singhvi, Ph.D., president and CEO. Low costs allow Novavax to build manufacturing plants across the globe. Rather than stockpiling vaccines, these sites would create it on demand, in response to an outbreak of pandemic flu and unimpeded by travel restrictions likely to be imposed in the event of a pandemic. Such facilities could also produce seasonal flu vaccines. “And because our lead time is several weeks rather than half a year, we’d be able to release a vaccine before the first wave of infection hits the local population,” Dr. Singhvi points out.
Novavax is also working on a vaccine against seasonal flu. While current seasonal flu vaccines consist almost entirely of the hemagglutin antigen, Novavax’ development-stage product includes neuraminidase and matrix protein as well, and is, therefore, potentially more effective, according to the company.
Boosting the Immune Response
Vaccine developers have long believed that the right adjuvant can make a huge difference in the immune response to a vaccine. To date, only one adjuvant—alum—has been approved in the U.S., but several are under development.
FDA has been guarded about approving new adjuvants due to safety concerns, says Marc Mansour, Ph.D., vp for R&D at Immunovaccine Technologies (IVT). “Regulators recognize that alum is inadequate in many cases, and that we need better adjuvants,” he says. “But FDA is approaching the issue cautiously.”
IVT announced late in 2007 that it had successfully scaled up the manufacturing process for Vaccimax®, its vaccine platform that includes antigens, adjuvants, and liposomes. This work validates the suitability of the platform for commercial applications in therapeutic cancer and infectious disease indications. IVT expects to get its cancer formulation into Phase I by the end of 2009.
The manufacturing development was performed at Dalton Pharma Services, a cGMP contract manufacturer and development company. IVT hopes to out-license the platform for vaccines to treat cancer and infectious diseases.
Currently, IVT’s development-stage vaccines, which use short, synthetic peptide antigens, are targeted to cancer of the prostate, ovary, and breast. IVT is also researching vaccines against pandemic flu based on the usual HA antigens.
Like many small companies, particularly vaccine firms, IVT’s business strategy involves developing vaccines through mid-late clinical stages, then finding a business or licensing partner. “This type of deal is common in the vaccine business,” notes Dr. Mansour.
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