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In general, gene therapy is carried out by introducing a therapeutic gene to produce the defective or the lacking protein. But there are certain disorders (cancer, viral and parasitic infections, and inflammatory diseases) which result in an overproduction of certain normal proteins. It is possible to treat these diseases by blocking transcription using a single-stranded nucleotide sequence that hybridizes with the specific gene, and this is called antigene therapy. Antisense therapy refers to the inhibition of translation by using a single-stranded nucleotide. Further, it is also possible to inhibit both transcription and translation by blocking the transcription factor responsible for the specific gene expression.

Nucleic acid therapy refers to the use of DNA or RNA molecules for therapeutic purposes. The naturally occurring sequences of DNA and RNA or the synthetic ones can be employed in nucleic acid therapy. Theoretically, there is a vast potential for use of nucleic acids as therapeutic agents. But most of the work that is being carried out relates to the use of RNA in antisense therapy. (Note: Some authors use antisense therapy in a broad sense to reflect antigene therapy as well as antisense therapy.)

Antisense therapy for AIDS

Attempts are also being made to prevent HIV infection through antisense therapy. The target cells for HIV infection are genetically engineered to contain a gene that can express a complementary copy of hiv genome. This gene produces antisense RNA. When the cells containing antisense RNA are infected by HIV, it binds to viral RNA forming double- stranded RNA-RNA hybrid molecules. This double-stranded molecule cannot be used by the enzyme reverse transcriptase. Consequently, a DNA copy of the HIV genome cannot be made and incorporated into the genome.