# Increased production of humoral factor and PD-L1 expression induced by cytokine stimulation play a key role in the immunosuppressive effects of stem cells derived from human exfoliated deciduous teeth

## TL;DR

Stem cells from baby teeth can suppress immune responses and help protect transplanted islets, making them a promising tool for islet transplantation.

## Contribution

SHED's immunosuppressive effects are stronger than BM-MSC and involve PD-L1 and humoral factors, offering a novel approach for islet transplantation.

## Key findings

- Stimulated SHED significantly inhibit PBMC proliferation and cytotoxicity.
- SHED enhance insulin secretion in reaggregated human pancreatic islets.
- Immunosuppressive effects of SHED are partially mediated by PD-L1 and cell contact.

## Abstract

Recently, the efficacy of mesenchymal stem cells (MSC) targeting transplant immunosuppression has been reported, and their application to islet transplantation is also expected. However, since the stability of functional manifestation of MSC remains unclear, we have investigated the stability and efficacy of cytokine-stimulated stem cells from human exfoliated deciduous teeth (SHED) in the human immune system in order to establish a safety clinical application.

SHED were stimulated with TNF-α, IL-1β, and IFN-γ, which were elevated post-transplant in the liver. Flow cytometry was used to analyze surface antigen expression. Human peripheral blood mononuclear cells (PBMC) were co-cultured with stimulated SHED directly or indirectly to assess PBMC proliferation. Cytotoxicity assay evaluated PBMC-induced damage to induced pluripotent stem (iPS) cell-derived human pancreatic beta-like cells. ELISA measured immunomodulatory factor secretion.

Programmed death-ligand 1 (PD-L1) expression was assessed, and PBMC were co-cultured with stimulated SHED in the presence of anti-PD-L1 antibody. SHED were also reaggregated with dissociated human pancreatic islets to generate islet-like organoids, and insulin secretion was measured. Stimulated SHED showed minimal change in cell surface markers but significantly inhibited PBMC proliferation and cytotoxicity, Stimulated SHED produced elevated levels of immunosuppressive factors and expressed PD-L1. The immunosuppressive effect was partially inhibited by inhibiting cell contact between SHED and PBMC or blocking the PD-1/PD-L1 pathway. Furthermore, insulin secretion was enhanced in reaggregated human pancreatic islets with SHED.

We demonstrated that the use of SHED in its activated state effectively suppresses immune response and maintains graft function at the time of islet transplantation.

•Addressing immune responses in islet transplantation remains the critical challenge in improving transplantation outcomes.•Immunosuppressive effects of SHED and BM-MSC were evaluated in the human immune system.•SHED-induced immunosuppression, mediated by humoral factors and cellular contact, was stronger than that by BM-MSC.•SHED also improved insulin secretion in reaggregated human islets, suggesting a promising adjunct for islet transplantation.

Addressing immune responses in islet transplantation remains the critical challenge in improving transplantation outcomes.

Immunosuppressive effects of SHED and BM-MSC were evaluated in the human immune system.

SHED-induced immunosuppression, mediated by humoral factors and cellular contact, was stronger than that by BM-MSC.

SHED also improved insulin secretion in reaggregated human islets, suggesting a promising adjunct for islet transplantation.