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Synthesis of Antigens Through Cloned Genes -  Hundreds of genes in eukaryotes have been cloned either from genomic DNA or from cDNA. These cloned genes included a number of genes for specific antigens, and in some cases have been used for the synthesis of antigens leading to the preparation of vaccines.
Following two examples can be used to illustrate the use of cloned genes for vaccine preparation:

(i) Cloning of Hepatitis B virus (HBY) genome. The HBV genome has been cloned in the plasmid pBR322 and propagated in E. coli. From this clone, antigen could be produced in good quantity, which reacted with hepatitis B core antibody (HBAb). This has therefore been used to produce hepatitis B vaccine, which was later approved for mass vaccination in several countries.

(ii) Cloning of human malarial gene. Despite the great menace and threat to human health due to malarial parasite Plasmodium falciparum, no anti-malaria vaccine, could be developed so far. Recently with cloning of a gene coding for surface protein of the sporozoite of P. falciparum, there is a hope for developing a vaccine.

In human host, malarial parasite passes. through several antigenically distinct phases, namely;
(i) sporozoite: the form in which the parasite is injected with mosquito bite; sporozoites enter the liver and multiply and develop into
(ii) merozoites, which in turn invade and multiply in red blood cells; small fraction of these merozoites in red blood cells form
(iii) gametocytes, which may be picked up by a mosquito to start another cycle.

Therefore, vaccines can be developed to control any of these phases and will be accordingly called
(i) antisporozoite vaccine, which will prevent malaria in the vaccinated individual and also block its spread;
(ii) antimerozoite vaccine which will protect or ameliorate the patient but will not check the spread of the disease and
(iii) antigametocyte vaccine, which would prevent the spread without helping the patient. Of these, antisporozoite vaccine is in sight due to cloning of gene meant for circumsporozoite (CS) protein.

This gene was obtained directly from DNA of erythrocytic form of parasite, rather than as cDNA from mRNA. This cloned gene may, in course of time, lead to the synthesis of vaccine b) synthesizing CS protein by cloned gene.

 
 

 

 
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