Vegf-A mRNA transfection as a novel approach to improve mouse and human islet graft revascularisation

Aims/hypothesis: The initial avascular period following islet transplantation seriously compromises graft function and survival. Enhancing graft revascularisation to improve engraftment has been attempted through virus-based delivery of angiogenic triggers, but risks associated with viral vectors have hampered clinical translation. In vitro transcribed mRNA transfection circumvents these risks and may be used for improving islet engraftment. Methods: Mouse and human pancreatic islet cells were transfected with mRNA encoding the angiogenic growth factor vascular endothelial growth factor A (VEGF-A) before transplantation under the kidney capsule in mice. Results: At day 7 post transplantation, revascularisation of grafts transfected with Vegf-A (also known as Vegfa) mRNA was significantly higher compared with non-transfected or Gfp mRNA-transfected controls in mouse islet grafts (2.11- and 1.87-fold, respectively) (vessel area/graft area, mean +/- SEM: 0.118 +/- 0.01 [n = 3] in Vegf-A mRNA transfected group (VEGF) vs 0.056 +/- 0.01 [n = 3] in no RNA [p < 0.05] vs 0.063 +/- 0.02 [n = 4] in Gfp mRNA transfected group (GFP) [p < 0.05]); EndoC-bH3 grafts (2.85- and 2.48-fold. respectively) (0.085 +/- 0.02 [n = 4] in VEGF vs 0.030 +/- 0.004 [n = 4] in no RNA [p < 0.05] vs 0.034 +/- 0.01 [n = 5] in GFP [p < 0.05]); and human islet grafts (3.17- and 3.80-fold, respectively) (0.048 +/- 0.013 [n = 3] in VEGF vs 0.015 +/- 0.0051 [n = 4] in no RNA [p < 0.01] vs 0.013 +/- 0.0046 [n = 4] in GFP [p < 0.01]). At day 30 post transplantation, human islet grafts maintained a vascularisation benefit (1.70- and 1.82-fold, respectively) (0.049 +/- 0.0042 [n = 8] in VEGF vs 0.029 +/- 0.0052 [n = 5] in no RNA [p < 0.05] vs 0.027 +/- 0.0056 [n = 4] in GFP [p < 0.05]) and a higher beta cell volume (1.64- and 2.26-fold, respectively) (0.0292 +/- 0.0032 mu l [n = 7] in VEGF vs 0.0178 +/- 0.0021 mu l [n = 5] in no RNA [p < 0.01] vs 0.0129 +/- 0.0012 mu l [n = 4] in GFP [p < 0.001]). Conclusions/interpretation: Vegf-A mRNA transfection before transplantation provides a promising and safe strategy to improve engraftment of islets and other cell-based implants