|Human Interferon Genes (HIG)
For the first time, Isaacs and Lindenmann isolated the interferon in 1957. Definition and nomenclature of interferon have been recommended by a committee of experts (Anonymous, 1980). Interferon is defined as "a protein which exerts virus non-specific antiviral activity, at least in homologous cells through cellular metabolic procedure involving the synthesis of both RNA and protein." Thus, interferon is secreted by human cells just to resist the immediate invasion by virus and multiplication of abnormal cells.
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:
According to origin of cells they are classified into two major groups : leukocyte interferon and fibroblast interferon. Leukocyte interferon is produced on large scale but major difficulty is that mass production of IFN-a cannot be done.
||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.
Later on hybrid plasmid containing cDNA of IFN-b genes was built up which needed a promoter site on plasmid to express in E. coli cells (Derynck et al, 1980). Similarly, hybrid plasmids were also prepared that contained IFN- genes with trap promoter between the leader and ribosome binding sites, so that expression of interferon could be done. Expression of both the interferon could be optimized by varying the spacing sequence between trap Shine- Dalgarno sequence and the initiator condon (Glover, 1984).
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.