For years, vaccine manufacturing has faced low prices and high liability, and companies have simply left the business, one by one. However, recent developments, notably concerns about Avian flu and a possible flu pandemic, have underscored the need for a vibrant, viable and competitive marketplace for vaccine products and technologies. The emergence of AIDS, SARS and West Nile Virus has only intensified concerns. Manufacturers who remain in the vaccine business are adopting multiple strategies, exploring simple steps like dilution and the use of new adjuvants, improving traditional manufacturing methods and exploring new ones such as cell culture vaccine manufacturing. At the same time, new vaccine media such as DNA vaccines are also being developed.
Last year, the U.S. flu vaccine shortage brought more attention to the issue of vaccine manufacturing, but in particular to flu vaccine manufacturing, which uses a complex method and occurs in fertilized chicken eggs. More than 70% of the global supply is produced in this manner by CSL, Ltd. (Parkville, Victoria, Australia), ID Biomedical (Northboro, Mass.), GlaxoSmithKline (London), Chiron (Emeryville, Calif.) and Sanofi Pasteur (Swiftwater, Pa.). “Eggs are the easiest medium for growing influenza virus, and provide a natural barrier against other pathogens,” says Vijay Samant, president of Vical (San Diego), a developer of DNA vaccines.
Egg-based flu vaccine production began about 35 years ago, and incremental improvements are made each year. Although manufacturers have slowly, steadily increased yields, the egg-based productivity well is running dry. “It would be unrealistic to believe that we’ll find ways to double yields, given current plant capacity,” says James Matthews, Ph.D., senior director, health and science policy, for Sanofi Pasteur U.S. At the same time, though, he says, “It would be a mistake to call the egg-based manufacturing method a dead end. It’s very predictable and reliable.”
To meet the growing demand for vaccine, Sanofi Pasteur has committed to doubling its manufacturing capacity and expanding its formulation and filling capabilities. If the company keeps its current plant — a big “if” at this point — its vaccine production will triple, but the new capacity is not expected to come online before 2009.
New technologies are being used to improve egg-based manufacturing efficiencies. One important example is disposable manufacturing equipment, which would help reduce cleaning and cleaning validation requirements and eliminate cross-contamination concerns. Since vaccines are not typically produced at a huge scale, the economic argument for using disposables is quite compelling, for both egg-derived and cell culture vaccines, says Hélène Pora, vaccine application development director at Pall Corp. (Saint Germain-en-Laye, France).
Dilution: how low can you go?
At the same time, studies are being conducted to determine the minimum effective dose of vaccines, especially for pandemic flu. The U.S. government, which is planning to stockpile close to eight million doses of an experimental vaccine against avian influenza by early 2006, has been encouraging production of agents to combat the deadly H5N1 strain, although no one knows how effective such a vaccine would be. Most experts believe immunization would require two inoculations, while a few hope that a mere fraction of the currently envisioned dose would be effective. Studies are under way on the feasibility of diluting the current stockpile to cover 120 million Americans. Even if fifteenfold dilution works, the U.S. will be far short of protecting all its citizens should a pandemic strain of bird flu emerge.
Vaccines often employ simple chemical agents, called adjuvants, to boost immunogenicity. Dowpharma (Midland, Mich.) is developing recombinant protein adjuvants for vaccines against influenza and other diseases. Dowpharma produces its LT protein adjuvant in Pseudomonas fluorescens.
Interest in adjuvants is on the rise as vaccine manufacturers seek to get more doses per unit vaccine. “All the major vaccine players are looking at adjuvant strategies for various vaccines, including flu,” says Kurt Hoeprich, Dowpharma’s business leader for vaccines.
Given the difficulty of substantially improving unit operations, manufacturers who use chicken eggs might focus on early-stage efficiencies, before the cultures are even set up. “Having the strains in hand and producing vaccine seed are the rate-limiting step,” says Kathy Coelingh, Ph.D., senior director for scientific and regulatory affairs at MedImmune (Gaithersburg, Md.). “Cutting down on this time will translate into clinical benefits.”
Culture wars
Rajeesh Beri, Ph.D., who manages process development at ID Biomedical, stresses the importance of having an alternative to egg-based manufacture, especially for flu vaccine. Certain influenza strains do not grow well in eggs. Moreover, a flu variant that originates in birds could kill chick embryos before sufficient virus was generated to create a product.
ID, which will soon be acquired by GlaxoSmithKline, is developing FluINsure, a nasally-delivered subunit vaccine. Subunit vaccines also offer the potential for rapid response to emerging viruses. ID also manufactures Fluviral S/F, a traditional egg-derived vaccine, and is developing NeisVac-C for meningitis C and a vaccine against group A strep in cell culture.
FluMist, MedImmunne’s lead nasal influenza vaccine product, is manufactured in chicken eggs, but the company has been investigating cell culture methods for some time. The potential benefits of growing viruses in mammalian cells are great, according to Coelingh, but it will take time to make the switch for seasonal flu.
FDA is “pretty comfortable” with using MDCK (Madin-Darby Canine Kidney) cells for pandemic influenza vaccines because of that disease’s high mortality. It will take much more data to convince the Agency to approve cell culture-based manufacturing for plain vanilla flu. That puts manufacturers in a bind of sorts, since playing the pandemic flu game forces them to dedicate manufacturing capacity to one influenza strain, which may never present a health problem. “There’s no point having that capacity for a one-shot deal,” says Coelingh.
Sanofi Pasteur is also developing cell-based production technology. Early in 2003, the company entered an agreement with Crucell (Leiden, Netherlands) to access the latter’s PER.C6 cell line for viral vaccine manufacture. PER.C6 cells are readily infected by influenza and, unlike other cells with that characteristic, they grow well in suspension. Sanofi Pasteur has also received a $97-million contract from the U.S. Department of Health and Human Services to develop a cell culture platform for influenza and pandemic flu.
But cell culture is no quick fix, Sanofi Pasteur’s Matthews warns. “Vaccine makers lack experience ‘campaigning’ flu strains in cell culture,” he cautions. “It will probably take ten years before that method is routine for flu vaccine production.”
Like flu vaccines made in eggs, experimental vaccines from cell culture need to protect against (and produce) three different viruses. “If you lack one strain, you lack a viable product,” Matthews says. Each of those viruses must be manufactured separately, since production facilities are not set up to manufacture more than one virus strain at one time.
Some vaccine developers are attempting to get around this limitation by development of “conserved” antigen subunit vaccines, which represent regions of the flu virus that do not change significantly from strain to strain, year to year. Researchers are hoping such a vaccine might provide lasting protection against multiple influenza variants, over many years perhaps, from a single shot. However, the first approved virus-based vaccine from cell culture will probably employ the “trivalent” strategy, just like the egg-derived product does today.
Familiar hurdles
Cell culture’s eventual success in vaccines, whether of the live/killed virus or subunit type, depends in part on overcoming the same hurdles it faces during the manufacture of conventional protein therapeutics: achieving high titers and culture viability, minimizing downstream losses, and regulations. Vaccines derived from killed or attenuated viruses require cells that are susceptible enough to virus infection that they promote viral replication, but not so vulnerable that the virus kills them. Also critical will be an efficient means of separating target viruses from cells and nondesirable pathogenic agents (viruses, prions).
According to cell culture expert Dr. Florian Wurm of the Swiss Federal Institute of Technology (Lausanne), advances in cell culture media are responsible for much of the hundredfold improvement in cell culture productivity over the last two decades. Similarly, successful cell culture-based vaccines, whether viral or protein, will demand careful attention to media composition and optimization.
Due to the unusual nature of growing viruses, cell culture-based viral vaccines will take some tweaking. Creative media formulations may promote cell growth but inhibit infection, notes Shawn Smith, bioproduction segment leader at media specialist Invitrogen (Grand Island, N.Y.). “Always keep the process goals in mind when optimizing the formulation,” he says.
Invitrogen claims to have participated in most of the major cell culture vaccine projects worldwide by providing media for established and experimental cell lines, including MDCK, Vero, and PER.C6. These cell lines have served the veterinary vaccine marketplace safely and efficiently for years.
Cell culture: curb your enthusiasm
More and more resources are being devoted towards non-egg-based vaccine production despite strong opinions favoring maintaining the status quo as well as for eventually abandoning eggs altogether. “There seems to be a sense of urgency to get out of eggs and into something quicker and more scalable,” says Invitrogen’s Smith. “But developers need to temper their enthusiasm.” With global regulations and the egg-based method firmly entrenched, he does not see substantial quantities of influenza vaccine manufactured outside of eggs for at least five to ten years. “The industry needs to get through the inertia of that first [U.S.] approval.”
“Cell culture is easy when it works,” says Samant of Vical. “But cells are hardly a utopia unless you’re talking about bacterial fermentation, which nobody is at the moment. Plus vaccines produced in mammalian cells would not be more effective than those manufactured using eggs. At best you’d enjoy some manufacturing advantages, but no efficacy benefits.”
Samant believes one possible direction for cell culture is to engineer a chicken embryo cell line for influenza vaccine incubation. These would have many of the benefits of eggs (which are actually embryonic chick cells), principally susceptibility to influenza viruses. At the same time, chicken cells would minimize the need to demonstrate clearance of pathogenic viruses that are generated endogenously in nearly all mammalian cell lines.
New science
The future of immunization may lie in products based on new science. Consider DNA vaccines. The idea behind them is simple: DNA coding for antigens from viruses or bacteria are injected into skin. Some of these genes wind up in the nuclei of cells, where they instruct the cell to manufacture the antigen that raises an immune response. When later challenged with the pathogen, the immune system kicks in and repels it.
The manufacturing angle for DNA vaccines is as compelling as the science behind them. At a typical dose of two micrograms, vaccinating every U.S. citizen twice would require only 1.2 kg of DNA, a quantity that can be made in a garage-sized plant. “At these levels, production becomes trivial, almost superfluous,” says John Beadle, M.D., CEO of PowderMed Vaccines U.S. (Frederick, Md.). Well, almost. The DNA must be formulated and filled in an appropriate delivery device. PowderMed uses a technology it calls PMED (particle-mediated epidermal delivery), which coats DNA onto gold microparticles using a sugary binding agent. The “injection” is actually a blast from a disposable delivery device which propels the particles into the epidermis, a tissue rich in immune-system cells.
PowderMed has four clinical and three preclinical projects based on this technology. Among these is a collaboration with GlaxoSmithKline for an HIV vaccine. The most developed pipeline product is a vaccine for human influenza, which recently completed Phase I trials with flying colors.
Vical’s DNA vaccine programs are also based on slightly different technology, and their product is injected by needle. The company’s development-stage products include three cancer vaccines, eleven products against infectious diseases, four cardiovascular vaccines, and three veterinary products.
Another interesting alternative vaccine platform is AVANT Immunotherapeutics’ (Needham, Mass.) attenuated bacterial scaffolds. AVANT begins with weakened salmonella, typhoid, or cholera bugs and attaches antigens from the target pathogen to the surface. The carrier organism serves not just as the vehicle, but as a type of independent immune booster—aa super-adjuvant if you will. “Our method goes cell culture one better because we’re growing bacteria, which is easy,” comments CEO Una Ryan, Ph.D. Attenuated bacteria-based vaccines provide almost immediate protection and are stable at room temperature for many months. AVANT and partner GlaxoSmithKline have one such vaccine, Rotarix (against rotavirus), approved in 34 countries, and several others in clinical trials.
In addition to providing process development and other knowhow for vaccines produced through bacterial fermentation, Dowpharma maintains its own vaccine technology platform based on virus-like particles (VLPs) which are generated in Pfēnex (pronounced “phoenix”) Expression Technology, a microbial expression system. The company has active programs against bacterial and viral pathogens, including influenza, for which it plans to team with an experienced vaccine developer for clinical evaluation and commercialization. VLPs employ an inert core festooned with protein antigens, typically molecules which are conserved through virus mutations. Dowpharma’s carrier is an antigenic but noninfectious plant virus. The other two major players in VLPs, Novavax (Malvern, Pa.) and Acambis (Cambridge, Mass.), use a different type of carrier. According to Hoeprich of Dowpharma, his team can construct a VLP in about six weeks, compared to three to six months to produce vaccines through the egg method.
DEATH BY ATTRITION?The steady attrition of vaccine capacity in North America over last 25 to 30 years has not been due to chance, says Donald F. Gerson, COO of Celltrion, Inc. (Inchon, Korea). Gerson knows of what he speaks. Since the mid-1980s, he has managed, by his estimation, the manufacture of between four and five billion doses of vaccines against tetanus, diphtheria, tuberculosis, cholera, measles and smallpox, for such firms as Wyeth, Aventis and Acambis. The vaccine industry’s troubles began in the 1950s, when several thousand children developed polio because of faulty manufacturing of the Salk polio vaccine. Although errors of that magnitude never occurred again, the incident has shaped the perception of the vaccine industry to this day. Considering vaccines’ enviable efficacy and safety record (conspiracy theories notwithstanding), manufacturers could never command a price commensurate with their products’ benefits. Uncertainty on the demand side didn’t help either. “Unless governments step in and purchases entire lots of vaccine, the price will always remain low, which almost guarantees marginal supplies,” says Gerson. However, even total co-opting of vaccine markets through government purchases may not solve manufacturers’ economic woes, as governments demand rock-bottom prices for drugs. This is especially true in developing nations, whose citizens most desperately need vaccines, but whose public health infrastructures cannot even afford the needles used to deliver these miracle medicines. “As many as two-thirds of the human race cannot afford vaccines of any type, in any form,” Gerson adds. Gerson is skeptical that even new manufacturing methods will save the day. Sanofi Pasteur (Swiftwater, Pa.) has received a huge contract to develop cell culture-derived flu vaccine. Baxter (Deerfield, Ill.), and Solvay Pharmaceuticals (Weesp, Netherlands), is investing heavily in methods to manufacture its InfluvacTC influenza product in MDCK cells. But the cost of building a vaccine manufacturing facility — estimates range from $50 million to $400 million — will keep all but the most dedicated manufacturers away. “It only takes standard execution of normal business practices to make cell culture manufacturing work,” says Gerson, “but it still takes a lot of money.” “Vaccine makers have been victims of their own success,” says Kathy Coelingh, Ph.D., senior director for scientific and regulatory affairs at MedImmune (Gaithersburg, Md.). “Vaccines are the most cost-effective medicines ever made, but society expects to have absolute protection with very little risk. But finally, the government is recognizing the importance of having a viable, incentivized vaccine industry that we can depend on, on American soil.” |
To access an article from HealthDay on a new approach that uses recombinant hemagglutinin (rHA) to produce vaccines more rapidly than conventional methods, visit www.healthday.com/view.cfm?id=531050.
