Coating of human pancreatic islets with CD4+CD25+CD127- T regulatory cells inhibits the rejection. A novel immunoprotective approach

N. Marek¹, A. Krzystyniak¹, I. Ergenc², L.W. Wang¹, R. Misawa¹, K. Golab¹, O. Cochet¹, X.J. Wang¹, S. Kozilel², P. Trzonkowski¹, J.M. Millis¹, P. Witkowski^1
1 University of Chicago, Surgery, Chicago, USA; ² Koç University, Istanbul, Turkey

Objective: Rejection and immunosuppression related toxicity compromisethe results of pancreatic islets transplantation. The aim of this studywas to determine, if T regulatory cells (Tregs) attached to islet cells couldmodulate the immune reaction and protect islets from rejection.

Methods: Human islets were coated with allogeneic ex-vivo expandedhuman Tregs using our previously developed protocol withbiotinylated poly(ethyleneglycol)-N-hydroxysuccinimide [biotin-PEG-NHS] attachedto both type of cells and streptavidin as a binding molecule.

Results: Attaching [biotin-PEG-NHS] to the surface of the islets and[biotin-PEG-NHS] with streptavidin to the Tregs prior to binding (coating) didnot affect their viability and function. Then, islets were coated with Tregs andthe bonds were stable in in vitro 4 day culture. Viability and function ofcoated islets were not compromised in comparison to non-coated islets incellular staining andi nsulin-secretion dynamic perfusion assays. After invitro incubation with allogeneic T effector cells, Treg-coated isletsrevealed preserved function with higher insulin secretion compared to controls-native, otherwise modified islets (coated with allo or auto PBMC) or when Tregswere added to the culture,but not attached to islets (p<0.05) (Figure). Additionally, ELISPOT assay revealed suppression of IFN-γ secretion, when Teffector cells were challenged with Treg-coated islets comparing to controls(99±7 vs 151±8 dots, respectively;p<0.009).

Conclusions: We demonstrated for the first time the ability to bindimmune regulatory cells to target cells with preservation of their viability andfunction. Allogeneic Tregs attached to the islets showed their protectiveactivity against immune attack. If these results are confirmed with invivo studies, local delivery of immunoprotective Tregs on the surface ofpancreatic islets may bean alternative to the currently used immunosuppression after islet transplantation.