Recombinant Vaccines II: Hepatitis B Overview

Recombinant and Synthetic Vaccines II

• Hepatitis B virus is transmitted via contaminated needles and sexual contact.
• It infects an estimated 200,000 Americans annually.
• Of the 20,000 who become carriers, one in five dies from cirrhosis and one in 20 develops liver cancer.
• Hepatitis B is a viral infection attacking the liver, causing acute and chronic disease.
• It is a significant occupational hazard for health workers, but preventable with available vaccines.
• A recombinant subunit vaccine exists for Hepatitis B.

Recombinant Subunit Vaccine for Hepatitis B

• The virus does not grow in tissue culture but can be obtained from carrier plasma.
• Vaccines purify viral surface antigens or inactivate the virus (e.g., with formaldehyde).
• The source of these vaccines is limited.
• Inactivated vaccines carry a risk of not completely inactivating all particles.

Hepatitis B Virus Structure and Vaccine Components

• The virus has small, medium, and large surface proteins (S, S+PreS2, and S+PreS2+PreS1).
• The viral envelope is primarily composed of S protein molecules (226 residues).
• Its genome is largely double-stranded DNA, encoding core and surface proteins.

Vaccine Production

• The gene for the surface protein is cloned from the viral genome.
• The DNA coding for the S protein is inserted into a yeast plasmid.
• Initially, yeast was used as the host to glycosylate the envelope protein.
• The protein is self-assembled into virus-like particles (VLP), which are indistinguishable from actual viral envelopes.

Recombinant Subunit Vaccine Advantages and Disadvantages

• Yeast-produced vaccines, while lacking some oligosaccharides, are effective.
• In 1986, it became the first recombinant DNA-based vaccine, licensed in the US.
• Earlier methods required substantial quantities of human serum to produce one dose.
• Modern methods obtain multiple doses from a single yeast culture volume.

Newer Vaccine Generation

• Newer vaccines use DNA for PreS2 and PreS1 regions (N-terminal parts).
• These regions appear to bolster immunity.

Vaccine Production in Mammalian Cells

• Plasmids containing the S protein gene and an animal cell promoter are introduced into mammalian cell lines.
• Translation occurs on ribosomes attached to the endoplasmic reticulum.
• Proteins are glycosylated and secreted as empty vesicles.
• This can induce immunity in individuals unresponsive to older vaccines.

Potential Problems of Recombinant subunit vaccines

• Recombinant vaccines, though effective, are often not replacing traditional ones.
• Economic reasons: Traditional vaccines are often effective and cause fewer adverse reactions.
• Scientific reasons: Some proteins fold improperly.
• Expression levels of specific genes can be problematic.
• Cultured mammalian cells used to express protective antigens may induce tumors when injected into animals.
• Removing host cell DNA can be difficult in order to prevent the introduction of tumor-causing DNA.
• Immunity produced is sometimes weak.