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Mar 1, 2012 (Vol. 32, No. 5)

Modernizing Vaccine Production

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    PaxVax has built a proprietary technology platform based on adenovirus serotype 4 (Ad4), which it says enables the rapid development of oral vaccines that can target any protein antigen.

    Emerging bird and swine flu variants during the past decade haven’t turned into the epidemics some feared, but they have still sent a firm message to governments and drugmakers: Current manufacturing procedures are not ready to produce enough vaccine fast enough to counter such threats. As a result, the U.S. government has invested heavily in vaccine production technology. Beyond filling a health need, it’s building up an arsenal of production and manufacturing systems to ensure that flu vaccines can be delivered efficiently in the face of biological threats. And vaccines for other pathogens are hitching a ride on the funding tailcoats, modernizing technology across the entire field. At the “World Vaccine Congress” next month, vaccine-makers will gather to discuss their innovations.

    “The pandemic threat that started eight years ago with avian flu is what really spearheaded this focal point to try to find a cell substrate that can handle high generation,” says Deborah Mosca, vp of product management at PaxVax. “We think novel cell substrates can respond much faster in the three-to-six month time frame with millions and billions of doses. And you can’t get there with eggs.”

    Modern flu vaccine production methods haven’t changed much since the 1950s, and are still egg-based. Vaccine manufacturers inject thousands upon millions of chicken eggs with virus and let them incubate for 9–12 days. Then the eggs are cracked, and the virus is purified and prepared into a vaccine.

    The process is slow, and occasionally entire batches of contaminated eggs have to be thrown out—hence the push toward cell-based production methods. “What makes cell culture attractive are the concerns about a bird flu,” says Tim Hahn, senior vp of manufacturing at NovaVax. “With a bird flu, the birds are infected, the eggs are infected, and eggs are used to make the vaccine.”

    At NovaVax, researchers are harvesting virus-like particles (VLPs) grown inside insect cells to use as vaccine antigens. VLPs contain proteins that mimic viral structure but lack genetic material. Thus the immune system will form antibodies to the viral proteins, but there is no danger of replication and infection.

    To generate the particles, the antigen sequence for pandemic or seasonal flu, two main disease areas at NovaVax, is encoded into a baculovirus, which then infects Sf9 insect cells grown in culture. Influenza spreads by budding new viruses off the cell membrane, and the researchers “keep that natural mechanism in the DNA coding,” says Hahn, so that the VLPs simply bud off the insect cell membrane. They’re then density-separated and purified, ready to generate an immune response.

    The insect-based method isn’t cheap, however, so NovaVax has turned to other aspects of manufacturing to save money. It grows its cultures inside disposable bags housed in stainless steel incubators, reducing cleaning costs between batches. Its purification system also has disposable parts for the same reason. “It saves on infrastructure, saves on time, and gives us a better turnout between batches,” reports Hahn.

    NovaVax’ seasonal flu vaccine will begin Phase II trials early this year, and it plans to begin human trials for a pandemic flu vaccine in the second quarter.

    It’s taken a long time to get to the point where companies could even consider testing cell culture-based vaccines in people because regulatory authorities were unsure of their safety. NovaVax had some paving laid before it because GlaxoSmithKline has already broken in the FDA with its Cervarix vaccine against human papillomavirus, which is VLP-produced using an insect-baculovirus system.

    “There has been tremendous resistance for introducing new cell types because of the unknowns,” says Mosca. “But when there’s been a need, there has been push and the regulatory authorities have acquiesced.”

    One way to baby-step the regulatory dance is to use protocols already widely accepted, and tie in a new innovation—and this is exactly what PaxVax is doing. The antigen for its pandemic flu vaccine is encoded on an adenovirus vector, which has been used in military vaccinations for decades. “We had the benefit of all the experience from the military,” says Mosca. “Ten million recruits have taken it over the years with no significant adverse events.”

    However, its real innovation is pioneering the use of a human cell line, A549, for use in vaccine production. Several human cell lines are already used to make vaccines, but one benefit of A549 is that it is immortal and thus can be used to continually produce vaccine proteins without having to restart cell cultures from scratch every 100 generations.

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