May 6, 2009
Blacksburg, Virginia -- Virginia Tech virologist Chris Roberts’ goal is to develop a platform for a flu vaccine that allows rapid modifications to meet new strains of flu.
Since 90% of complicated flu cases occur among those over 65, Roberts, associate professor in biomedical sciences and pathobiology in the Virginia-Maryland Regional College of Veterinary Medicine, has been working on a novel flu vaccine for the elderly. That is still his aim, but he is now more motivated than ever to speed development of his cell culture-based vaccine technology that is more rapid than the egg-based growth system presently used to create vaccines.
Influenza is an enveloped virus. It obtains its envelope or membrane as it buds from the surface of the host cell it has invaded. Roberts is using this practice against the virus - introducing membrane-bound immune-system stimulatory molecules such as cytokines into cells in such a way that the virus will incorporate them as part of its envelope. “Using this approach, inactivated influenza vaccines can be created that have enhanced immunogenicity, meaning they can boost our immune response to the vaccine and hopefully provide better protection against invading viruses,“ Roberts said.
Normally, cytokinescytokines are secreted proteins that boost and direct the immune system’s response to inflammation and infections. When a foreign particle gets into the body, the body ultimately responds by stimulating:
1) B cells to secrete anti-viral antibodies,
2) cytotoxic T cells to kill infected host cells, and
3) helper T cells to regulate and control the response of both cell types.
Antibodies work by recognizing and binding to specific components of the virus such as the glycoproteins on the surface of the virus (envelope). This serves to neutralize the ability of the virus to infect cells in the respiratory tract. A vaccination introduces weakened or killed forms of a virus so that the body recognizes the pathogen and begins producing antibodies to fight it. These antibodies are then ready to fight off infection should they encounter the virus.
Roberts’ vaccine goes a step further and provides an immune-boosting signal on the surface of the vaccine.
“It would stimulate your body’s defense mechanisms so that you develop a more potent response to that vaccine and that should translate into better protection against whatever flu is circulating at the time,“ said Roberts.
Presently, vaccines are made from eggs and it generally takes one or two special pathogen-free eggs per dose. It also takes four to five months to prepare enough doses of the vaccine for a given year. Several companies are actively working to develop cell culture based vaccines for flu, such as is already used for polio and chickenpox vaccines, for instance. “The process could someday allow us to reduce the amount of time required to make flu vaccines,“ said Roberts. “Cell culture based vaccines would also help us respond more rapidly when new viral strains emerge.“
Roberts’ approach, to have the virus clothed in its own vaccine, capitalizes on the use of cell culture based systems for vaccine production. Roberts’ group uses molecular biology techniques to fuse specific cytokines to components of the viral glycoproteins that facilitate their recognition by the virus assembly machinery. The resulting cytokine fusion proteins are then expressed in a virus permissive cell line and are actively incorporated into newly formed virus particles once those cells are infected with the virus. Now, when the virus leaves its host cell, it has cytokines bound to its outer surface and these particles are harvested, purified, and then chemically inactivated to create the vaccine. Importantly, these “killed vaccines,“ which Roberts’ has dubbed FLU CYT-IVACs (for FLU CYTokine bearing Inactivated VACcine), still retain the bioactivity of cytokines.
» Advantages of the Cell Culture System
This work was supported by the National Institute of Allergy and Infectious Diseases. The results of the mice trials have been published in the April 24, 2009, issue of Virology Journal (“Membrane-bound Cytokines Augment Influenza Virus Vaccines and Protect Against lethal Challenge in Mice,“ by Andrew S. Herbert, Lynn Heffron, Roy Sundick, and Paul C. Roberts). He and his collaborators also recently published a vaccine study in poultry in the January 2009 Journal of Interferon and Cytokine Research (“A Novel Method to Incorporate Bioactive Cytokines as Adjuvants on the Surface of Virus Particles,“ by Yufang Yang, David Leggat, Herbert, Roberts, and Sundick).