8.1 Modification by in vivo and ex vivo gene therapy

Somatic cells are modified in a number of different ways

8.1.1 Gene supplementation

This method is also called as gene augmentation. It aims to supply a functional copy of the defective gene. The method is generally employed for a gene product that has lost its function or is showing inadequate expression of protein. The process can be used when there is irreversible damage of the gene. The gene supplementation can be used for cancer therapy to increase the immune response against the tumor cells. Alternatively it can be used to replace the defective tumor suppressor gene.

8.1.2 Gene replacement

In this the mutated or nonfunctional copy of the gene is replaced by the correct functional copy of the same gene. The gene replacement is performed for a mutated gene which is harmful for the host. In general gene replacement aims for gain of function.

8.1.3 Targeted inhibition of gene function

The targeted inhibition of gene function is relevant for the infectious diseases where specific gene of pathogens is targeted. The pathogen associated antigenic gene is knocked down in order to avoid the harmful effect of the protein. It also aims for targeted inhibition of tumor antigen to reduce the autoimmune response. The gene is silenced by various means including siRNA, RNAi, etc.

8.1.4 Targeted killing of the cells

The targeted killing aims specifically for cancer cells where the metastatic form of the tumors are targeted and killed in situ . Many novel viruses called oncolytic viruses are targeted to kill the cancerous cells. Paramyxoviruses belong to such group of promising oncolytic viruses. Many studies using paramyxoviruses have shown encouraging results in reducing the cancerous condition by specifically targeting and killing the cancer cells by apoptosis.

Facts about gene therapy The beginning of gene therapy trial for humans started in 1990 for Severe Combined Immune Disorder (SCID). ajority of the gene therapy trials are conducted in United States and more than 60% of those are approved for cancer based gene therapy trials.