Human Interferon Genes (HIG)
Interferon is used to cure many viral diseases such as common cold and hepatitis. It is species specific. In man there are 3 classes of interferon:
- Alpha interferon (IFN-a) or leukocyte interferon (leukocytes of blood)
- Beta interferon (IFN-b) or fibroblast interferon (fibroblast of connective tissue).
- Gamma interferon (IFN-γ) or immune interferon (by lymphocytes of blood) and lymphoblastoid interferon by transformed leukocytes.
In 1980, IFN-a and IFN-b were successfully produced from genetically engineered E. coli cells (by isolation of mRNA from leukocytes and fibroblasts, production of cDNA, its integration into pBR322 and incorporation and cloning into E. coli cells). Production was estimated to be about 1,000 to 100,000 molecules of IFN-b per cell. The Swedish firm, Biogene, produced IFN-a and IFN-b through recombinant DNA techniques which are now under clinical trials. It was found that genes responsible for the production of IFN- a and IFN-b had 865 and 836 nucleotides, respectively.
IFN-b produced by genetically engineered microorganism showed lower specific activity and decreased stability than natural one. Enhanced specific activity and stability was obtained when the cysteine at position 17 was replaced by a series of site specific mutagenesis resulting in ‘IFN-b-Ser’ molecule. It was stable for two years and well tolerant in cancer patients. Moreover, genetically engineered E. coli is reported to yield 5-10 million units/ml of IFN-b-Ser in a 200 liter batch reactor within 2-3 days of fermentation.