Expression of transforming growth factor-beta by human islets: impact on islet viability and function

Transforming growth factor-beta1 (TGF-beta1) is a pleotropic cytokine that promotes angiogenesis and extracellular matrix protein synthesis in addition to its immunosuppressive effects. The purpose of this study is to identify optimal conditions for in vivo expression of TGF-beta1 by human islets to exploit the possible beneficial effects and minimize undesirable side effects. We transduced human islets with adenoviral vectors encoding the active form of Ad-TGF-beta1 or Ad-LacZ to test the effects of TGF-beta1 gene expression on islet in vivo function following their transplantation into a NOD-SCID mouse model. Islets were transduced with multiplicity of infection (MOI) of 20, 10, 5, and 2.5 per islet cell. At a MOI ranging from 2.5 to 20, expression of TGF-beta1 in islet supernatant persisted for 1-2 months and ranged from 153 +/- 5 to 2574 +/- 1299 pg/ml, respectively. Transduction with the lowest MOI (2.5) did not compromise the in vivo production of human C-peptide. We conclude that TGF-beta1 expression in transplanted islets does not compromise viability and that adenoviral transduction with the TGF-beta1 gene has a dose-dependent effect, with larger MOIs being deleterious. The data also indicate that in vitro culture system and the in vivo NOD-SCID model could be used successfully to evaluate the nonimmune effects of gene transduction.