One of the main bulwarks against an avian influenza ("bird flu") pandemic is vaccination against this disease. Since the specific virus or viruses capable of spreading this infection have not yet appeared, such a vaccine cannot yet be manufactured. If and when that microbe emerges, developing, producing, distributing, and applying that treatment to millions of people in the shortest possible time will be a high priority.
Unfortunately, the "legacy" method of producing vaccines, which involves inoculating fertile chicken eggs with live virus; growing the virus in the eggs; extracting, purifying, and inactivating it; and preparing it for injection in vaccine recipients is time-consuming, complicated, and subject to contamination. You can learn more about these problems by clicking on the title of the
Etopia Media Medical News Network article entitled
"Chiron Corporation fouls up multiple times, is rewarded with key role in global response to possible H5N1 bird flu pandemic, and cashes out, while co-founder repeats discredited Proposition 71 economic promises at legislative hearing".
A promising alternative to producing vaccines by this "legacy" method is to produce "DNA vaccines." For some basic introductory information about DNA vaccines, as provided on the web site of
Vical, a San Diego, California-based bio-technology pioneer of this technology, click
here.
In order to spread understanding of this possible alternative to legacy vaccine production,
Etopia Media Medical News Network submitted a list of questions about DNA vaccines to Vical, which has now provided detailed answers to these questions.
Etopia Media Medical News Network's questions and Vical's answers about DNA vaccines are presented here:
1. Heightened interest in DNA vaccines is taking place in the context of a looming avian influenza threat and perceived problems with legacy vaccine production methods. What is the legacy method of making vaccines and what are its limitations?
Conventional flu vaccines use split, killed influenza viruses or live, attenuated (disabled) influenza viruses. Other conventional vaccines are based on specific components of the target pathogen, which can be produced or extracted from the pathogen itself or manufactured synthetically.
The currently approved influenza vaccines are all manufactured by a conventional process that involves growing the influenza virus in chicken eggs. There are concerns about purity and consistency of vaccine produced by this method, but the major shortcomings relate to capacity. For the seasonal flu, availability of pathogen-free chicken eggs is based on orders placed well in advance, and therefore cannot be substantially increased on short notice. In a pandemic situation in which avian flu may affect entire flocks of chickens, the availability of eggs could be dramatically reduced at the time when they are most needed.
Purity is a concern if eggs from uncontrolled sources must be used to fill a gap. Chicken eggs may contain human pathogens and other impurities that could contaminate the resulting vaccine. And because the process involves multiple steps that are subject to incomplete control, potency and consistency of the resulting product can be variable.
Efficacy is another concern, particularly in the elderly, a population group that needs the most protection. The seasonal flu shot provides mainly B-cell mediated protection against a surface glycoprotein, which is different for each strain of flu. That is the reason you need to get a new flu shot each year. The live-attenuated inhaled vaccine has some potential to provide some protection against more conserved proteins, but the evidence of such cross-strain protection is limited.
There has been much discussion in recent months about changing to a cell culture manufacturing method for these conventional vaccines. While that would eliminate the reliance on eggs, it would also eliminate the role of the eggs as a “filter” for human pathogens, potentially increasing the risk of unrelated disease being passed along by the vaccine itself. This would require a more rigorous purification process that could render the vaccine ineffective.
Cell culture manufacturing can be very complex, and productivity may be much lower than with egg-based processes. That could further reduce availability of vaccine.
Regulatory approval of a vaccine using the cell culture manufacturing process requires approval of the cell lines themselves.
2. What is the basic theory underlying DNA vaccination?
DNA vaccination is based on the discovery that living cells in the body can take up DNA and produce the protein encoded by that DNA. A DNA vaccine “programs” cells to produce a protein associated with the target pathogen. The immune system then mounts a defense against the protein and is prepared to attack the actual pathogen when it arrives.
3. What is a "plasmid" and where do they come from/how are they made?
A plasmid is a closed loop of DNA, typically including a gene encoding the protein of interest and other sequences that control the cell’s internal manufacturing processes. Because of their structure, plasmids are inherently stable.
The plasmids used in DNA vaccines are typically assembled synthetically from the basic building blocks of DNA. They are then inserted into bacteria, which multiply in fermentation tanks making many copies of the plasmid. Straightforward purification processes then separate the desired plasmids from the unwanted bacterial remnants.
4. Let's say you wanted to use a DNA vaccine to protect people from avian influenza. What would the process be?
The first step in manufacturing a DNA vaccine is to identify the precise gene sequence of the specific strain of virus. This could be the current H5N1 strain of avian flu, or some as-yet-undetermined strain of an avian/human flu combination. From the gene sequence, specific genes can then be synthesized and inserted into plasmids. From that point forward, the process is identical to that used for any DNA vaccine, using simple fermentation and purification steps to produce the vaccine in the quantities needed.
5. Are these specifically-tailored plasmids infectious themselves?
No. Because plasmids encode only specific proteins associated with the pathogen, there is no possibility that they can produce the entire pathogen. Perhaps equally important for the manufacturer, there is no need to handle the pathogen itself to create the DNA vaccine. Only the gene sequence of the pathogen is needed. That means safety for employees and those in the surrounding communities are not at risk.
6. How are the DNA segments included in them able to stimulate the generation of antibodies in patients specifically effective against a specified antigen?
The proteins encoded by a DNA vaccine can be either surface antigens or core proteins from the target pathogen. The production of these proteins by the cells in the body results in specific responses against those proteins by the immune system. These immune responses can be either B-cell (antibody) mediated against surface proteins or T-cell mediated against core proteins. The combination allows targeting of specific features of the pathogen that may not be targets of an immune response during a natural infection.
7. How strong and how long-lasting is the immunity conferred by DNA vaccines?
That depends on the specific pathogen, just as with any other vaccine. This is a function of the immunogenicity of the specific features of each pathogen. Some may require multiple doses and periodic booster vaccines. Others may provide long-term protection with a single injection.
8. What are the advantages of DNA vaccines over legacy vaccines, in terms of ease of development, development time, side effects, production rate, and cost?
Compared with conventional vaccines, DNA vaccine development time and ease are significantly better, potentially cutting months or even years out of the process from initial identification of a pathogen to the point that a vaccine is ready for human testing. Side effects from DNA vaccines are really a function of immune responses against the encoded proteins, and may include local inflammation, redness, soreness, and other typical immune reactions. DNA itself does not cause any substantial side effects.
To date, the process has been performed on a much smaller scale for DNA vaccines, but the fermentors currently used for protein manufacturing could be converted to plasmid production. Production is theoretically scaleable to large fermentation and purification vessels that could yield millions of doses from each batch.
9. Where in the development and regulatory pipeline are various DNA vaccines from Vical, especially ones designed to work against influenza, and, more specifically, what trials or experiments are in place now to incorporate existing avian influenza DNA into DNA vaccines?
Vical and its licensees have vaccines at various stages of development, from early research through commercialization. The two grants received from the NIH to support influenza vaccine research are fairly recent (both in 2005), and these programs are therefore in relatively early stages of development. The current focus on avian flu is to develop and test a vaccine in mice and ferrets in collaboration with St. Jude Children’s Research Hospital. The two-year grant awarded in September is intended to support the program through preclinical development.
10. When an avian influenza virus mutates into one capable of routine human-to-human transfer, making a pandemic possible, how long do you expect it would take Vical to create a DNA vaccine against it and now long would it take to create commercially-useable quantities of that vaccine?
We were able to produce the initial vaccine construct for the SARS virus within 3 months of the completion of its genetic sequencing. Theoretically, a DNA vaccine could be developed and produced well within the six-month target recently announced in the President’s pandemic response plan.
In the absence of any financial restrictions or regulatory requirements, the process could be completed in substantially less time than that required by conventional vaccine processes. But because DNA vaccines are relatively new, the requirements for approval are likely to be higher than for conventional vaccines.
11. Would changes in regulatory and licensing procedures be necessary to enable such a rapid deployment scenario? What changes? Is this being attended to now?
Emergency authorization for development and manufacturing could be implemented as needed to address an impending pandemic situation. These measures are among those addressed in the President’s recently-announced plan. In the meantime, development must continue on the normal schedules associated with any new vaccine.
12. Are you talking to national and international health authorities (HHS, WHO) about your involvement in anti-avian flu initiatives, trials, plans, and funding?
We have announced funding under two NIH grants, one for human influenza and one for avian influenza. These efforts are closely related, and work on one largely applies to the other. It would be inappropriate for us to comment beyond these publicly-announced programs.
13. Is Vical publicly-traded? What's its symbol?
Vical is publicly traded on the Nasdaq National Market under the symbol VICL.
14. How completely does Vical control the intellectual property/patents covering DNA vaccine technology?
Vical and its collaborators discovered the core technology underlying DNA vaccination in the late 1980s, and our patents have been the basis for multiple licensing agreements.
15. Anything else you think the public ought to know about DNA vaccines and Vical?
Vical has recently been brought to the attention of many people because of our link to avian influenza. We would like these people to look beyond our avian flu effort to the broad range of other programs under independent and partnered development, all based on our patented technology. Our technology is broadly applicable for DNA vaccines, cancer immunotherapies, and angiogenesis programs. We would encourage interested parties to check our web site at
www.vical.com for a more complete picture of the company.
