Pancreatic islets engineered to display on their surface a novel form of FasL protein survive indefinitely by inducing tolerance through phagocytes/CD4+CD25+FoxP3+ Treg cell axis (141.47)

Abstract

Abstract Objective: Pancreatic islets engineered to display on their surface a chimeric form of FasL (SA-FasL) protein survive indefinitely in allogeneic recipients. In this study, we tested the role of phagocytes and CD4+CD25+FoxP3+ Treg cells in the induced tolerance. Methods: To study the function of Treg cells, OT-I transgenic and rag-/- B6 mice were adoptively transferred with 1 x 106 CD4+ Teff cells from naïve B6 together with 2-5x103 Tregs from na ïve, rejected, or tolerant animals one day prior to BALB/c islet Tx. The function of phagocytes in the induced tolerance was investigated using liposome-encapsulated clodronate for depletion. Results: OT-I mice did not reject BALB/c mice islet grafts (n= 5; >100 days) due to the restricted TCR repertoire for ovalbumin. Adoptive transfer with sorted 1x106 CD4+ Teff cells from naïve B6 mice promptly rejected allogeneic islets (n=5; MST=29.0±9.2 days). Cotransfer of 2-5x103 Tregs from long-term (n=5; >100 days), but not rejecting (n=5; MST=34.4±3.5 days), animals prevented graft rejection. Treatment with clodronate resulted in depletion of phagocytes and acute rejection of SA-FasL-engineered islets (n=5; MST=22.7±10.4 days). In marked contrast, 5/6 mice treated with control liposome accepted their grafts (MST>100 days). Conclusions: Tolerance to SA-FasL-engineered pancreatic islets is maintained by Treg cells that require phagocytes for induction. NIH (R21 DK61333, R01 AI47864, R21 HL080108), ADA (1-05-JF-56), and AHA Fellowship 0725348B.