Gene delivery

The addition, substitution, or ablation of DNA sequences may be achieved by any of the following:

♦ Injection of naked DNA into skeletal muscle by simple needle and syringe.

♦ DNA transfer by liposomes (delivered by the intravascular, intra-tracheal, intraperitoneal, or intracolonic routes).

♦ DNA coated on the surface of gold pellets that are air-propelled into the epidermis (the 'gene gun').

♦ Biological vehicles (vectors) such as viruses and bacteria. Viruses are genetically engineered not to replicate once inside the host. They are currently the most efficient means of gene transfer.

Other techniques involve fusion of whole cells or viral envelopes, elec-troporation, micro-injection, or chemical precipitation of DNA into cells.

The efficiency of transfer of therapeutic DNA required (dictated by the nature of the genetic defect) influences the choice of vector e.g. for gene replacement, high-efficiency viral vectors are desirable, whereas short-term gene expression to prime an immune response or sensitize cells to radiotherapy may be achieved by liposomal delivery.

Some of these strategies can be achieved ex vivo by transfer of a therapeutic gene into isolated cancer or non-cancer cells that are then reimplanted into the host. Others require delivery and expression of genes to target cancer cells in vivo (at much lower efficiency than ex vivo transfer) by exploiting transcriptional differences of specific genes between cancer and normal cells. The efficiency of gene transfer also varies greatly according to cell type targeted (low in neural and haemopoietic cells; high in myocytes, fibroblasts, hepatocytes; and variable among different tumours).

0 0

Post a comment