The induction of antigen (Ag)-specific tolerance represents a
therapeutic option for autoimmune diabetes. We demonstrated that administration
of lentiviral vector enabling expression of insulinB9-23 (LV.InsB) in
hepatocytes, arrests β cell destruction in pre-diabetic NOD mice, by generating
InsB9-23-specific FoxP3+T regulatory cells (Tregs). LV.InsB in combination with
a suboptimal dose of anti-CD3 mAb (combined therapy, 1X5µg CT5) reverts
diabetes and prevents recurrence of autoimmunity following islets
transplantation in ~50% of NOD mice. We investigated whether CT optimization
could lead to abrogation of recurrence of autoimmunity. Therefore, allo-islets
were transplanted after optimized CT tolerogenic conditioning (1X25µg CT25). Diabetic
NOD mice conditioned with CT25 when glycaemia was <500mg/dL, remained
normoglycaemic for 100 days after allo-islets transplantation, displayed
reduced insulitis, but independently from the graft. Accordingly, cured mice
showed T cell unresponsiveness to InsB9-23 stimulation and increased Tregs
frequency in islets infiltration and pancreatic LN. Additional studies revealed
a complex mechanism of Ag-specific immune regulation driven by CT25, in which
both Tregs and PDL1 co-stimulation cooperate to control diabetogenic cells,
while transplanted islets play a crucial role, although transient, recruiting
diabetogenic cells. Therefore, CT25 before allo-islets transplantation
represents an Ag-specific immunotherapy to resolve autoimmune diabetes in the
presence of residual endogenous β cell mass.