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Free «Hepatitis B Vaccine Production Using Yeast» Essay Sample

Background Information

Content Overview

The discovery of the hepatitis B advanced beyond protecting people through blood transfusions from hepatitis B to the broader scope of protecting people from the disease. In the late 1960s, virologist Blumberg (Fox Chase Cancer Center (FCCC), Barbara Werner, immunologist, Manfred Bayer electron microscopist, and molecular biologist Lawrence Loeb, vigilantly described the small particles isolated from HBsAg-positive blood and visualized it through the electron microscope.They found out that some particles were whole viruses, others contained no nucleic acid that was the genes responsible for causing infection and the disease (Harford & Cabezon, 234-87).

It is from such assumptions that Hepatitis B virus (HBV) was identified as the causative agent of serum hepatitis. Blumberg first acknowledged this antigen as a serum protein explicit for aborigines in Australia. It was only later that the infectious nature of the antigen was identified, in which case it turned out to be the surface protein of HBV that is secreted into the bloodstream of infected patients in excess over viral particles.

After many centuries, the first licensed vaccines against HBV became accessible in the beginning of 1980s.The vaccine was produced by harvesting and purifying HBsAg from the serum of chronic carriers, given that there was no possibility for proliferation of the virus in vitro (Gleeson & Ortori, 45-76). Even though they were safe and effective, serum-derived vaccines were expensive and in relatively short supply because of shortage of human carrier plasma that met the requirements for the production of the vaccine. Since the 1980s, recombinant hepatitis B vaccines have been used as more practical alternatives with the HBsAg produced in yeast (Harford & Cabezon, 234-87).

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HBV was established to be prevalent in many parts of the world, with more than two billion people having had contacted the virus, and more than 350 million people being chronic carriers of the virus.

Hepatitis B Vaccine Production Using Yeast

Why Yeast?

Yeasts have outstandingly been distinguished as capable of producing a potential vaccine against hepatitis B virus. This is a biological fact that has been founded on the rising track record of the expression platforms in the production of pharmaceuticals. Some of the commercially available, yeast-derived, recombinant pharmaceuticals are inclusive of insulin, the anti-coagulant hirudin, interferon-alpha-2a, and a variety of vaccines used against the hepatitis B virus and papillomavirus infections.

The yeast vaccines are particularly produced in either baker's yeast, known as Saccharomyces cerevisiae, the methylotrophic species Hansenula polymorpha and Pichia pastoris. For the case of this manuscript however, methylotrophs is considered in the production process for hepatitis B vaccines. The reason attached is that Methylotrophs yeast species produce a comparatively   high balanced production of both the membrane and the protein component of a recombinant viral particle (Gleeson & Ortori, 45-76).

Among the most significant recombinant pharmaceuticals available were the yeast-derived vaccines that could be used against hepatitis B infections. The vaccines for Hepatitis B were derived from the particles containing hepatitis B surface antigen (HBsAg) inserted into host-derived membranes.

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The development of effective, yeast-derived recombinant hepatitis B surface proteins was hence the factor behind the success of current vaccination programs against hepatitis B.

In the most recent advancements, yeast-based HepB vaccines are being modified by including substitute adjuvant, in addition to RC-529, a non-toxic lipid, A mimetic35. Other developments incurred along include the coming of large surface antigen also called core protein sequences aimed at reducing the number of non-responders or developing a therapeutic vaccine. Several combination vaccines are also under development, including yeast-derived HepB particles

What about Hepatitis B?

The hepatitis B virus is transmitted parenterally by infected blood through the mucosal routes, during organ transplantation, or parentally during birth. The most infected body organ by the virus is mainly the liver tissue. The virus infections can be transient or chronic.

Chronic hepatitis B develops in up to between (5 and10) % of the infected healthy adults and up to 90% of the newborns. After a persistent hepatitis B infection, the liver eventually develops cirrhosis. However, even without preceding cirrhosis, the development of hepatocellular carcinoma (HCC) is possible. Nearly 90 percent of the infected adults recuperate completely after the apparent or in-apparent hepatitis and may be regarded as cured (Gellissen, 321-76). Presently, there are two recombinant hepatitis B vaccines which have been approved by the FDA and accessible for use. The two are both S-antigen vaccines produced in the yeast S. cerevisiae, and P. pastoris. H. polymorpha-based vaccines have additionally been launched (George, Gotthard & Gerd, 121-45).

The production of recombinant H. polymorpha strains generally adhere to a standard approach synonymous to that prescribed for S. cerevisiae.This encompasses the construction of the expression cassette for HBsAg (contained in a plasmid vector), transformation of H. polymorpha, isolation and characterization of recombinant strains. Manufacturing of such H. polymorpha strains use vectors, inserting an S-antigen coding sequence into an expression cassette harboring either an FMD promoter or a MOX promoter for expression control. In addition, the vectors contain genetic elements that are necessary for plasmid propagation and selection in E. coli, and those for selection in the yeast host (Gellissen, 321-76).

The engineered strain contains up to 60 copies of the functional expression cassette for HBsAg mitotically stable and is integrated into the genome. FMD promoter-controlled production strains have been engineered for Hepavax-Gene AgB, like-wisely, MOX-promoter controlled strains have been engineered for ButaNG (Roggenkamp & Hansen, 35-65). The inherent features of the two promoters, both derived from genes of the methanol utilization pathway levels, providing both high and attractive productivity upstream process design that can be controlled by additions of appropriate amounts of glycerol and methanol to the culture medium.

In the H. polymorpha, the recombinant viral surface antigen is found to be assembled into yeast-derived lipid membranes similar to the situation in other yeasts, forming 22 nm, (1.17-1.20) g cm -3 particles (Roggenkamp & Hansen, 35-65).  Preceding studies have shown that this lipoprotein particle structure is necessary for the antigenicity of the HBsAg. the H. polymorpha-based platform with its methanol pathway promoters, and that including methanol in a fermentation process provides an efficient process for a balanced co-production of both vaccine components.

This is pegged in the knowledge that generally, membrane proliferation is associated with methanol induction (George, Gotthard & Gerd, 121-45).

Concluding Remarks

With the coming of gene technology, new methodologies for the production of safe and efficient pharmaceuticals, with the bacterium Escherichia coli, mammalian cells, and various yeasts as preferred platforms for the production of such recombinant compounds, have been provided. Newborns of chronically HBV-infected mothers can receive a combined active and passive immunization, all commercially accessible recombinant vaccines produced in yeasts.


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