Vaccine production

The basic process technology in vaccine production consists of fermentation for the production of antigen, purification of antigen, and formulation of the final vaccine. In bacterial fermentation, technology is weU estabHshed. For viral vaccines, ceU culture is the standard procedure. Different variations of ceU line and process system are in use. For most of the Hve viral vaccine and other subunit vaccines, production is by direct infection of a ceU substrate with the vims. 

Alternatively, some subunit viral vaccines can be generated by rDNA techniques and expressed in a continuous ceU line or insect ceUs. Recent advances in bioreactor design and operation have improved the successful production of IPV in large-scale bioreactors. However, roUer bottles or flasks are stiU used for most current vaccine production. Development of insect ceU culture will allow for very large-scale Hquid suspension culture (143). Several vaccine candidates such as gpl60 for HIV and gD protein for herpes have been demonstrated in the insect ceU culture system. However, no vaccine has been approved for human use. 

A large and rapidly growing number of clinical trials (phase I and phase II) evaluating the potential of DNA vaccines to treat and prevent a variety of human diseases are currently being performed ( http // clinicaltrials.gov) however, there is yet no licensed DNA vaccine product available for use in humans. The clinical trials include the treatment of various types of cancers (e.g., melanoma, breast, renal, lymphoma, prostate, and pancreas) and also the prevention and therapy of infectious diseases (e.g., HIV/ABDS, malaria, Hepatitis B vims, Influenza vims, and Dengue vims). So far, no principally adverse effects have been reported from these trials. The main challenge for the development of DNA vaccines for use in humans is to improve the rather weak potency. DNA vaccines are already commercially available for veterinary medicine for prevention of West Nile Vims infections in horses and Infectious Hematopoetic Necrosis Vims in Salmon. 

The starting point for the produchon of all microbial vaccines is the isolation of the appropriate microbe. Such isolates have been mostly derived from human infections and in some cases have yielded strains suitable for vaccine production very readily in other cases a great deal of manipulahon and selechon in the laboratory have been needed before a suitable strain has been obtained. 

Viruses replicate only in living cells so the first viral vaccines were necessarily made in animals smallpox vaccine in the dermis of calves and sheep and rabies vaccines in the spinal cords of rabbits and the brains of mice. Such methods are no longer used in advanced vaccine production and the only intact animal hosts that are used are embryonated hens eggs. Almost all of the vims that is needed for viral vaccine production is obtained from cell cultures infected with vims of the appropriate strain. 

For these proteins, mammalian cells proved better hosts, as they could process the protein with intracellular machinery similar to that in humans. However, large-scale production of proteins in cell culture was problematic. Mammalian cells had to grow attached to a solid surface, such as glass in roller bottle culture. While the Federal Drug Administration (FDA) had approved some processes for vaccine production that used cell cultures, it required that these cells be normal. Normal mammalian cells can divide only a few times before they stop growing, making scale-up to large volumes difficult. 

Diphtheria and tetanus vaccines are two commonly used toxoid-based vaccine preparations. The initial stages of diphtheria vaccine production entail the growth of Corynebacterium diphtheriae. 

The toxoid is then prepared by treating the active toxin produced with formaldehyde. The product is normally sold as a sterile aqueous preparation. Tetanus vaccine production follows a similar approach. Clostridium tetani is cultured in appropriate media. The toxin is recovered and inactivated by formaldehyde treatment. Again, it is usually marketed as a sterile aqueous-based product. 

The advent of recombinant DNA technology has rendered possible the large-scale production of polypeptides normally present on the surface of virtually any pathogen. These polypeptides, when purified from the producer organism (e.g. E. coli, Saccharomyces cerevisiae) can then be used as subunit vaccines. This method of vaccine production exhibits several advantages over conventional vaccine production methodologies. These include ... 

A number of mineral-based substances display an adjuvant effect. Although calcium phosphate, calcium chloride and salts of various metals (e.g. zinc sulfate and cerium nitrate) display some effect, aluminium-based substances are by far the most potent. Most commonly employed are aluminium hydroxide and aluminium phosphate (Table 13.13). Their adjuvanticity, coupled to their proven safety, render them particularly valuable in the preparation of vaccines for young children. They have been incorporated into millions of doses of such vaccine products so far. 

Haemophilus influenzae Type B Conjugate Vaccine Products ... 

A competitive assay could also be used for quantitation. In a competitive assay, unlabeled antigen competes for labeled antigen. Examples include ELISAs for vaccine product antigens, such as recombinant proteins from viruses, or nonvaccine antigens such as growth factors or cytokines. 

Product variants can also be generated by in-process procedures, such as those used for viral inactivation, for example. These procedures could alter the protein structure, forming new epitopes. These types of changes could potentially be detected by ELISA because of the specificity of the antigen-antibody interaction. In the case of vaccine production, an ELISA could be used to monitor viral inactivation. For this, a panel of MAbs, if available, could be used. 

To conclude, an issue that is bringing great attention in recent years, the production of chimeric virus-hke particles should be briefly analysed. These chimeric VLPs are potentially valid systems for broader vaccine production, i.e. against a large number of different serotypes [34] in addition they can result in safe combination vaccines between closely related viruses [35], can be able to carry multiple foreign epitopes [36-39], or even, with the incorporation of tags (e.g. polyhistidine), allow easy single-step product recovery [40,41]. 

The option of business as usual is unattractive, given the high benefit to cost of existing and yet-to-be-developed vaccines. Failure to change public policy will lead to underinvestment in R D and vaccine production capacity and a dearth of suppliers. Potential benefits for new vaccines for HIV/AIDS and malaria are extremely high, and for a disease such as avian flu, inventing new vaccine production processes is clearly of critical importance as well. 

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