Monogenic recessive diseases only require the functional gene to be expressed, often therapeutically useful levels being much lower than that those found in normal individuals. Many gene therapy protocols to date have concentrated upon treatments for cancer. The aim of immunopotentiation is to enhance the response of the immune system to cancers, thereby leading to their destruction. The cells are then irradiated prior to being returned to the patient, preventing the reintroduction of replication competent tumour cells. These approaches have been termed cancer vaccines.
Oncogene inactivation uses the same techniques employed for dominantly inherited monogenic diseases.
The oncogene may be targeted at the level of the DNA, RNA transcription or protein product. Oligodeoxynucleotides are short single stranded pyridimine rich DNA sequences that form a triple helix with purine rich double stranded DNA sequence. An alternative means of killing a tumour cell is to transduce a gene coding for a toxic product, known as molecular chemotherapy. Many cancer chemotherapy regimes are limited by their low therapeutic index, as determined by heamopoetic cells. Development of therapies for non malignant diseases have been hampered by the short duration of transgene expression.