Vaccine Production through Biotechnology

Vaccines work by exposing the immune system to a harmless version or component of a disease-causing pathogen, training the immune system to recognise that pathogen and mount a rapid, protective response if it is ever encountered again in its full, disease-causing form. Traditionally, vaccines have been made either from a killed (inactivated) whole pathogen or from a live but deliberately weakened (attenuated) strain of the pathogen, both of which stimulate immunity while (ideally) being unable to cause the actual disease.

Both traditional approaches carry certain risks and limitations. An inactivated pathogen must be produced by growing large quantities of the actual disease-causing organism before killing it, which requires strict biosafety precautions, and an attenuated live pathogen, while generally very effective, always carries some risk -- however small -- of reverting to a disease-causing form, or of causing illness in individuals with a weakened immune system.

Recombinant DNA technology offers a different, generally safer approach: rather than growing the whole pathogen at all, only the specific gene coding for a single protein found on the pathogen's surface -- a protein that the immune system recognises and responds to, called an antigen -- is identified, cut out, and inserted into a suitable host organism (commonly yeast, or occasionally a bacterium or cultured animal cell) using the same principles of recombinant DNA technology described earlier in this chapter. The host organism then expresses and produces large quantities of just that one antigenic protein, which is purified and formulated into a vaccine. Because the vaccine consists only of one protein component of the pathogen rather than the complete, intact organism, it is often called a subunit vaccine, and because the pathogen itself is never grown or handled at any point in the production process, there is no risk whatsoever of the vaccine causing the actual disease.

The recombinant Hepatitis B vaccine is a well-known example of this approach. The gene coding for a specific surface antigen protein of the Hepatitis B virus (called HBsAg) is inserted into yeast cells, which then express and produce large quantities of this one viral surface protein. This purified protein, entirely free of any other viral genetic material or infectious component, is formulated into the vaccine that is administered to patients, where it stimulates a protective immune response against Hepatitis B without ever exposing the patient to the live or even inactivated virus itself. …