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In the most simplified terms, a vaccine is a biological preparation that provides active acquired immunity against a certain disease. Usually a vaccine consists of a biological agent that represents the disease-causing microorganism. It is often made from a weakened or killed form of the microorganism, its toxins or one of its surface protein antigens. An individual that has been vaccinated produces antibodies against the protein antigen that protect him/her from contracting the disease upon attack from the pathogenic microorganism. Learn More »
Scientists take many approaches to design vaccines against a pathogenic microorganism. These choices are dictated by the nature of pathogen and the infection as well as practical considerations about the use of the vaccine. Some of the options include live attenuated vaccines, inactivated vaccines, DNA vaccines and recombinant subunit vaccines. See schematic below for an overview of the various approaches used to make a vaccine. This technical note discusses the basics of research and production of recombinant vaccines.
Vaccine generated using recombinant DNA technology is called recombinant vaccine. While there are various types of vaccines made possible by recombinant DNA technology, recombinant vaccines can be classified into two major categories.
These vaccines usually consist of synthetic DNA containing the gene that encodes the disease-agent protein. Usually, the plasmid DNA used as vaccine is propagated in bacteria such as E. coli and they are isolated and purified for injection. This "naked" DNA is usually injected intramuscularly or intradermally. The principle behind a DNA vaccine is that the antigen can be expressed directly by host cells in a way that simulates viral infection and invokes an immune response from the host. This is similar to GenScript's DNA Immunization Technology which is a powerful tool that aids in custom antibody production against membrane proteins, other problematic antigens, as well as for early DNA vaccine development studies. DNA immunization technique allows antigen production to occur in vivo, bypassing the need to produce and purify protein antigen in vitro. Click here to learn more about how GenScript's DNA immunization service can help you succeed in your next DNA vaccine development project. Schematic below illustrates concept of DNA vaccine.
A DNA vaccine usually consists of the following components:
The promoter drives the expression of the gene encoding antigenic protein, when introduced into the target. The protein antigens can be processed in the cytoplasm and the fragmented peptides presented to the immune system by class I MHC molecules. In addition, if the protein is exported or secreted, it can be processed by class II MHC molecules and, as a result, mount a specific antibody response.
GenScript is a world leader in synthetic DNA technology and its rush gene synthesis service helped Novavax develop a vaccine candidate for avian influenza A/H7N9 in record time of 289 days, less than 6 weeks after initial reports of infections in April 2013. Click here to learn more about how GenScript gene synthesis services can accelerate your vaccine research.
These are subunit vaccines containing only a fraction of the pathogenic organism. Often time these are synthetic peptides that represent the protein component that induces an immune response. But they can also consist of protein subunits (antigens) expressed in a heterologous expression system (E. coli, yeast, insect etc.) using recombinant protein expression technologies. Most of the vaccines under investigation today are based on such purified recombinant proteins or subunits of antigens. One of the best examples of recombinant protein vaccine currently in use in humans is the vaccine against Hepatitis B Virus (HBV).
The current vaccine for Hepatitis B Virus is produced by expressing the HBV surface antigen (HBsAg) using yeast expression system. Yeast secretes the antigen into culture supernatant facilitating purification. Yeast post translational machinery is suitable for this purpose as it renders the Antigen with the necessary glycosylation patterns. Upon recombinant expression, the HBsAg assembles into virus-like particles (VLPs) which are extremely immunogenic, making it a very effective vaccine.
Another example of a recombinant protein vaccine is the vaccine against Human Papilloma Virus (HPV). There are currently two vaccines against HPV infection, both of which have been developed based on VLPs assembled from recombinant HPV coat proteins. These vaccines utilize the L1 recombinant capsid protein of the virus subtype produced either in insect or yeast-expression system.
Prokaryotic expression systems for vaccine antigen production include bacteria such as E. coli and eukaryotic systems include mammalian, yeast or insect cells. Several factors are taken into consideration before selecting the right system for vaccine antigen expression. Among other things, expression levels, selection marker and the presence or absence of post-translational modification are essential factors that interfere in the efficacy of production of recombinant antigens as vaccines. Bacterial expression systems are widely used due to the ease of handling and their capacity for high level expression. However, for antigens in which post-translational modifications are necessary, the use of mammalian, yeast or insect cells is considered.
Although vaccines based on recombinant proteins offer several advantages such as safety and economy of production, most of them suffer from poor immunogenicity when administered alone. And hence they require the use of adjuvants to elicit a longer-lasting immune response.
At GenScript, E. coli expression is routinely used for the production of high quality recombinant protein used in vaccine research applications. Baculovirus expression is also widely used given its applicability to a wide variety of proteins, their authentic modifications (resembling antigenic protein) and also for cost reasons. To see an overview of recombinant protein expression systems, click here.
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