Hepatitis B [Recombivax HM (Merck) — A Hepatitis B Vaccine]
8.4. Hepatitis B [Recombivax HM (Merck) — A Hepatitis B Vaccine]
The Recombivax HB (Merck), a hepatitis B vaccine, is one of the most recent and significant developments in the field of recombinant DNA technology, that essentially comprise of highly specific antibodies which act like magic bullets.
It has been duly observed that hepatitis tends to cause a severe acute infection and may ulti- mately lead to chronic infection and permanent liver damage. It is essentially caused by hepatitis B virus (HBV) ; and recognized as an enveloped and double-stranded DNA virus. It has been adequately revealed through meticulous studies that individuals who are at the most vulnerable and greatest risk for infection include : IV-drug abusers (e.g., morphine/heroin addicts) ; homosexual men ; HBV-infected mothers ; and above all the health care workers. It is now almost mandatory under stringent law-enforc-
* WHO :WHO Expert Committee on Biological Standardization ; 44th Report, WHO Tech. Rep. Ser. 848,
PHARMACEUTICAL BIOTECHNOLOGY
ing authorities that ‘Blood Banks’ must now routinely screen for the HBV-antigens, which practice has substantially minimised the obvious exposure and risk for infection in persons requiring multiple trans- fusions. Previously called serum hepatitis. Importantly, the hepatitis B infection may be prevented through a vaccine created using recombinant DNA technology. However, complete protection can be accomplished via two vaccinations 1 month apart and a third dose 4 months later ; an increased anti-HBs antibody titer value evidently shows successful vaccination. The following categories of person(s) must
be vaccinated : • All health care staff members • Patients with renal disease requiring hemodialysis • Police personnels and other public safety workers • Family members and sexual partners of those infected with HBV • Persons who travel frequently and extensively abroad.
Note : The Centres for Disease Control and Prevention (CDCP) recommends that pregnant women should be meticulously tested for HBs Ag so that the newborns can be vaccinated.
Caution : Individuals who have not been vaccinated against HBV and receive a needle stick or mucous membrane contact either with blood or with other body secretions should immediately contact their occupational health department.
Fig. 2.15 evidently illustrates the various steps being followed in a sequential manner with regard to the production of a genetically engineered vaccine e.g., Hepatitis B Vaccine.
HEPATITIS VIRUS
4. Gene is removed Genetic material
3. Gene that directs
into yeast cells (DNA)
1. Genetic material
production of surface
5. Plasmids are inserted
from viral DNA
is extracted from
protein is located
and inserted
hepatitis virus
into plasmid
Yeast cell
Plasmids containing
Surface proteins that provoke
gene for an immune
surface response
2. Individual genes
analyzed and
6. Yeast is grown by proteins are
8. Result is a large quantity
fermentation. Cells combined with
of pure surface protein
reproduce and generate preserving
particles that provoke
more surface protein agent and other ingredients to
an immune response
7. After 48 hr yeast
cells are ruptured
make vaccine
to free surface protein. Mixture is processed to extract and purify surface protein
Fig. 2.15. A Schematic Diagram Illustrating a Genetically Engineered Vaccine.
GENETIC RECOMBINATION
Step 1 : Genetic material (DNA) is dul extracted from the ensuing hepatitis virus. At this stage the ‘surface proteins’ essentially provoke an immune response.
Step 2: The ‘individual genes’ are adequately analyzed and identified. Step 3 : The ‘specific gene’ which categorically directs production of surface protein is located
carefully. Step 4 : In this most critical steps the gene is removed from the viral DNA and inserted into the
plasmid carefully. Step 5: The plasmids are meticulously inserted into the corresponding yeast cells. Step 6 : Yeast is allowed to grow via fermentation. In this manner the cells reproduce and gener-
ate more quantum of surface protein. Step 7 : After a duration of 48 hours the corresponding yeast cells are ruptured to free the ensu-
ing ‘surface protein’. The resulting mixture is duly processed so as to extract the purify the surface protein.
Step 8 : A large amount of surface protein particles, in its purest form, are obtained which ultimately provoke an immune response effectively.
Step 9 : The resulting surface proteins are adequately mixed with appropriate preservations together with other ingredients to obtain the vaccine.
Antigenic Markers for HBV-Infection
In fact, there are three antigenic markers that have been duly identified for the HBV infection, namely :
(a) HBsAg : a surface antigen located on the viral envelope that represents one of the earliest markes and appearing in the blood during incubation,
(b) HBeAg : obtained from the protein capsid surrounding the DNA, and also is a marker for causing active infection, and
(c) HBc :
A core antigen that does not circulate in the blood, and helps in the stimulation of the production of the primary antibodies against HBV. These antibodies are not protective and, hence, provide no immunity.