INSULIN DELIVERY BY SOMATIC-CELL GENE-THERAPY

The feasibility of somatic cell gene therapy as a method of insulin de livery has been studied in mice. Murine pituitary AtT20 cells were tra nsfected with a human preproinsulin DNA in a plasmid containing a meta llothionein promoter and a gene conferring resistance to the antibioti c G418. The AtT20MtIns-1.4 clone of cells was selected because of its higher insulin-releasing activity compared with other clones. After cu lturing for 24 h in Dulbecco's medium containing 10 mM glucose, the At T20MtIns-1.4 cells released human insulin at about 5 ng/10(6) cells pe r 24 h. Insulin release was not significantly altered by raised concen trations of glucose, potassium or calcium, but insulin release was inc reased by 20 mM arginine, 5 mM isomethylbutylxanthine and 90 mu M zinc . AtT20MtIns-1.4 cells (2 x 10(6)) were implanted intraperitoneally in to non-diabetic athymic nude (nu/nu) mice, and the mice were made diab etic by injection of streptozotocin after 7 days. Release of human ins ulin in vivo was assessed using a specific plasma human C-peptide assa y. Human C-peptide concentrations were maintained at about 0.1 pmol/ml throughout the 29 days of the study. The development of streptozotoci n-induced hyperglycaemia was delayed in recipients of the cells releas ing human insulin, compared with a control group receiving an implant of non-transfected cells. At autopsy the implanted AtT20MtIns-1.4 cell s in each recipient had formed a tumour-like aggregation, with an oute r region of insulin-containing cells. The study suggests that somatic cell gene therapy offers a feasible approach to insulin delivery.