Hepatitis is a viral disease that causes acute and chronic liver infection.
It is one of the deadly virus infection which affects almost 7 million people a year.
This severe and contagious disorder can be prevented by the use of hepatitis-B vaccination.
The hepatitis B vaccine was produced previously by the use of the live hepatitis virus.
This version of the vaccine was a live vaccine as it had the viral particles which are devoid of virulence.
The virulence is removed by attenuation so that they are no longer pathogenic. So, when introduced into the body, the body’s immune system develops antibodies to combat them. Thus the immunity to new infection develops.
But these vaccines are unsafe and non-reliable due to problems of emergence of virulence in immune-compromised patients. Also, there is a trend of decline in the immunity of humans.
So once administered the vaccines can turn virulent and cause infection.
To avoid this, and provide effective prevention, hepatitis-B subunit vaccines are used.
These vaccines are manufactured using genetic engineering technology.
The subunits vaccines are the antigens of the virus and can evoke an immune reaction.
Further, these subunits are not the virus as a whole so no chances of virulence.
But the subunits are hard to collect and even multiply as they are not organisms. Further their size is also very small.
So the steps in the production of the hepatitis B vaccine are quite lengthier than routine steps of five steps of genetic engineering.
Production of Hepatitis B Vaccine
1. Isolation of the Whole-genome of the hepatitis-B virus:
2. Cloning of the genome with plasmid and its multiplication
3. The release of the sequence coding for HBs antigen.
4. Ligate with a yeast expression vector
5. Transform in Saccharomyces and allow for vaccine formation.
Isolation of the genome from the virus is the first step. An entire genome of 2kb is isolated which codes for HB ag on the virus body. But the quantity can be less and viruses are also not readily multiplied in labs. So the gene is multiplied by the use of plasmid. The plasmid has the inherent tendency to multiply. These plasmids with genome are introduced into bacteria for replication and multiplication. Many plasmids with the gene are produced.
From these sufficient genomes, the required gene coding for HBs is cleaved by the use of restriction endonucleases.
These are the enzymes that cut DNA molecules at precise points.
Once the required gene is formed, it is again taken and cloned with another vector namely yeast expression vector.
Here the yeast expression vector has alcohol dehydrogenase-1 (a strong promoter gene) by the side. Also, there is leucine 2 as a marker.
The enzyme DNA ligase is used for ligation (cloning) of the gene with yeast vector.
Then this newly formed vector is transformed into Saccharomyces cerevisiae bacteria.
The transformed cells are allowed to grow in culture media and promote gene expression. The vaccine is formed and is present in the body of the bacterial cell.
The bacterial cells are lysed, and the solution is centrifuged.
By this, the HBs gene is obtained in the supernatant. This vaccine is isolated and allowed to form aggregates with silver.
Unlike routine steps of rDNA technology, here we use two vectors. One for the multiplication of viral genes. The other is to transfer the HBs gene into bacteria from where it is expressed.
The hepatitis B vaccine is given as an intramuscular injection. It is administered as three doses and the second and third doses are given after one month and six months respectively.