Taming autoimmunity: Alpha-1 antitrypsin overexpressing mesenchymal stromal cells promote regulatory T cell crosstalk to reverse diabetes.

Mesenchymal stem/stromal cell (MSC) therapy holds promise as a therapeutic option in diabetes treatment. Anti-inflammatory and immunomodulatory activities are enhanced when MSCs are engineered to overexpress alpha-1 antitrypsin (AAT-MSCs). Because a single infusion of AAT-MSCs reversed new-onset diabetes in over 50% of the female non-obese diabetic mice, we used single-cell RNA sequencing, flow cytometry, and functional analyses to characterize how AAT-MSCs modulate CD4+ and CD8+ T cells in pancreatic lymph nodes (PLNs) and islets. AAT-MSC treatment increased T regulatory cells (Tregs) and more effectively suppressed T cell proliferation when stimulated with anti-CD3/CD28 antibodies. Treated mice exhibited reduced T helper 1 cells and CD8+ cytotoxic T cells. In vitro studies confirmed the capacity of AAT-MSCs to promote Treg expansion in both mouse and human cells, drive CD8+ T cells toward an exhausted phenotype, and enhance mouse and human islet cell survival. CellChat analysis showed that AAT-MSC therapy strengthens intercellular communication, especially signals originating from Tregs toward other PLN and islet cell populations. These findings clarify how AAT-MSCs modulate immune response and support their potential clinical application for type 1 diabetes and other autoimmune or inflammatory conditions.