CCL22-expressing Stem Cell-derived Islet Grafts Recruit Regulatory T Cells in Mice

Abstract

Background: Cell therapy using human donor or stem cell-derived islets (SC-islets) to replace lost insulin-producing beta (β) cells holds great promise for type 1 diabetes. Recruiting regulatory T cells (Treg) through chemokine signaling could mitigate allo- and autoimmune attack on transplanted β-cells, potentially obviating the need for immunosuppressants. We hypothesized that SC-islets genetically engineered to secrete the chemokine C-C motif chemokine ligand 22 (CCL22) would attract Treg to the site of transplantation and may ultimately prolong graft survival.

Methods: We engineered human embryonic stem cells to express CCL22 and differentiated them into SC-islets. CCL22 + SC-islets were assessed for gene and protein markers of endocrine cells and tested for function in vitro by glucose-stimulated insulin secretion assay, and in vivo by transplanting SC-islets into immune-deficient, streptozotocin-treated diabetic mice. Next, CCL22 bioactivity was confirmed by Transwell Treg migration assay. Treg migration was tracked using bioluminescent imaging of mice with CCL22 + SC-islet grafts and infused with luciferase-expressing Treg.

Results: The expression of CCL22 did not adversely impact the differentiation into SC-islets, as confirmed by gene and protein analysis and functional tests in vitro and in vivo. CCL22 + SC-islets induced Treg migration in vitro, with specificity to CCL22 confirmed by a C-C motif chemokine receptor type 4 antagonist. Furthermore, CCL22 + SC-islet grafts recruited human Treg to the transplant site.

Conclusions: CCL22 + SC-islets are functional and capable of attracting Treg. By recruiting Treg, CCL22 + SC-islets may create a tolerogenic immune environment for SC-islets after transplantation.