 |
Development of vaccines for immunity Biotechnology is used in three different ways in the development of vaccine: a) Separation of a pure antigen using a specific monoclonal antibody. The method of immunopurification using monoclonal antibodies is used, to separate specific antigen from a mixture of very similar antigens. Once purified, the antigen is used for developing vaccine against a pathogen. Individual interferons (which have the property of inhibiting viral infection and cell proliferation) have been purified using this technique. These interferons were later used for clinical trials and then commercially used. Hundreds of genes in eukaryotes have been cloned from genomic DNA or from cDNA. These clones genes included a number of genes for specific antigens and some have been used for the synthesis of antigens leading to the preparation of vaccines. A very good example of this is cloning of Hepatitis B virus (HBV) genome. The HBV genome was cloned in the plasmid pBR322 followed by it’s propagation in E.coli. The antigens produced from this clone reacted with hepatitis B core antibody (HBAb) which has been used to produce hepatitis B vaccine. Efforts are on to use this method to produce an Anti- malarial vaccine. Malarial parasite Plasmodium falciparum is the malarial parasite which has become a major threat to human health which spreads by the mosquito bite. In human body, the malarial parasite passes through several antigenically distinct phases viz. sporozoite, merozoite, gametocytes etc. The vaccines can be developed to control any of these phases hence we can have antisporozoite vaccine, antimerozoite vaccine etc. Out of all these, considerable progress has been made in the making of antisporozoite vaccine due to cloning of gene meant for circumsporozoite (CS) protein. This protein 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 by synthesizing CS protein by clone gene.Synthetic peptides as vaccines Vaccines can also be prepared through short synthetic peptide chains. There are several ways by which these can be used as vaccines. As it is the three dimensional structure (not the amino acid sequence) of the protein which is responsible for the immunogenic response, it is essential to find out the protein region involved in immunogenic response. E.g. in Foot and Mouth Disease virus (FMDV), the amino acid 114-160 of virus polypeptide can produce antibodies which can neutralize FMDV and provide protection. The region of 201-213 amino acids of the same protein also could neutralize FMDV hence it has been shown that small synthetic peptides representing these regions of proteins can show immunogenic response and can be used for the development of vaccine. The immunogenic region of protein can also be located by gene coding for the protein. E.g. in Feline leukaemia virus, the clone gene of an immunogenic protein was cut into fragments by DNAase I and then cloned in lambda phage. Phage colonies (plaques) with different cloned fragments are screened with a specific monoclonal antibody that neutralizes the pathogen. The fragments which react with antibody must be synthesizing the immunogenic peptide fragments which can be sequenced. Using this method it was possible to identify a 14 amino acid immunogen of the envelope protein of Feline leukaemia virus (FLV). The corresponding synthetic peptide was also found to compete with the virus for antibody. The immunogenic region of a protein in a pathogen can also be identified by eluting it from purified major histocompatibility complex (MHC) molecules. Different MHC allelic variants bind with different proteins and purified using specific T cells. Peptides can be eluted from these purified MHC molecules and later on sequenced. The sequenced peptides are used to make synthetic peptides which are used as vaccines. |