(i) Recombinant vaccines : Vaccine is produced using recombinant DNA technology. A recombinant vaccine contains protein or a gene encoding a protein of a pathogen origin that is immunogenic A gene coding an immunogenic protein from the pathogen, is isolated, cloned and used for vaccine production The vaccines based on recombinant proteins are also called Sub-Unit Vaccines.
Whole protein vaccine : Hepatitis B vaccine is produced from surface antigens of transgenic yeast by r-DNA technology They can also be produced in genetically engineered microbes, cultured animal cells, possibly in insects and plants.
Recombinant – polypeptide vaccines : In some cases, the immunogenic portion of the protein- recombinant polypeptide is used as vaccine e.g., gene encoding B polypeptide (part of cholera enterotoxin – Ab A2 and B polypeptide) has been cloned and the recombinant B polypeptide produced is being used, in combination with inactivated cholera cells, as an oral vaccine in place of conventional injectable cholera vaccine. Immunogenicity of foot and mouth disease virus coat protein is due to its amino acids 114-160 and also 201 -213. They induce antibodies which neutralize the virus and thereby provide protection against the foot and mouth disease.
Live recombinant vaccine : The most advanced and promising approach in which concerned pathogen gene is introduced into the genome of selected viral / bacterial vector which is suitably attenuated and the live microorganisms are used for vaccination. Vaccinia virus appears to be more promising vector.
DNA vaccines: Recently vaccines based on pathogen naked DNA are being developed. Tue various approaches for DNA vaccines are as follow
• injection of pure DNA (or RNA) preparation into muscles
• reimplantation of autologus cells (cells of the individual to be vaccinated) into which the gene has been transferred and
• particle gun delivery of plasmid DNA which contains the gene in an expression casette e.g., skin cells They elicit humoral immune response and are usually shed off in a few days preventing long term persistence modified cells.
(ii) Delayed fruit ripening
A major problem in fruit marketing is the pre-mature ripening and softening dining transport of fruits. Consequently shelf-life of fruit remains short in the market. During ripening, genes encode the enzyme cellulase and polygalacturonase. Therefore, ripening process can be delayed by interfering the expression of these genes. In the U.S.A., a transgenic tomato named FlavrSavr (flavour saver) was produced where ripening is delayed by , lowering polygalacturonase activity.
A plant growth hormone ethylene is produced during fruit ripening and senescence. It is synthesised from S-adenosylmethionine through an intermediate compound 1-aminocyclopropane-l-carboxylic acid (ACC). There is a large number of bacteria that can degrade ACC. Therefore, bacterial gene (for ACC) deaminase associated with ACC degradation was isolated and introduced into tomato. In transgenic tomato, fruit ripening was delayed because it synthesised lower amount of ethylene (due to inhibition in ACC synthesis) than the normal tomatoes. Such tomatoes and other fruits can be transported to a longer distance without spoilage.
