Killing of Human β-Cells by CD8+ T Cells Triggers Inflammatory Paracrine Signaling and Neighboring β-Cell Dysfunction

Type 1 diabetes is a progressive autoimmune disease characterized by the selective destruction of insulin-producing β-cells by CD8+ T cells. Although the mechanisms of antigen-specific β-cell killing are well established, the broader consequences of this targeted destruction on neighboring β-cells that escape direct T-cell receptor (TCR)-mediated attack remain poorly understood. Here, we developed a coculture model of HLA-A2-expressing human β-cells cultured as pseudoislets and CD8+ T cells specific for the INS15-24 epitope. Using this new in vitro model, we demonstrate that 1) β-cell death induced by CD8+ T cells strictly depends on TCR-HLA class I interactions and 2) neighboring β-cells that evade direct T-cell contact do not alter β-cell identity or glucose-stimulated insulin secretion. However, they exhibit increased expression of inflammatory markers, reduced insulin content, and impaired protein translation. The robust, versatile, and readily applicable model described here represents a strong basis to further address paracrine signaling that extend beyond direct cytotoxicity.

In type 1 diabetes, CD8+ T cells destroy pancreatic β-cells. Since most β-cells avoid direct T-cell contact, we asked whether bystander effects drive their dysfunction and loss. We asked whether CD8+ T cells can damage β-cells indirectly via bystander inflammation. By developing and using a chimeric pseudoislet model, we show that β-cell killing requires direct CD8+ T-cell contact, contact-free β-cells are impacted by inflammation, that these effects are reproduced using conditioned medium from activated CD8+ T cells, and that insulin secretion is preserved with reduced storage and impaired protein translation. Our model provides a platform to dissect type 1 diabetes pathogenesis and test therapies to preserve β-cells.