CD103 Expression Is Required for Destruction of Pancreatic Islet Allografts by CD8⁺ T Cells

The mechanisms by which CD8 effector populations interact with epithelial layers is a poorly defined aspect of adaptive immunity. Recognition that CD8 effectors have the capacity to express CD103, an integrin directed to the epithelial cell-specific ligand E-cadherin, potentially provides insight into such interactions. To assess the role of CD103 in promoting CD8-mediated destruction of epithelial layers, we herein examined the capacity of mice with targeted disruption of CD103 to reject pancreatic islet allografts. Wild-type hosts uniformly rejected islet allografts, concomitant with the appearance of CD8⁺CD103⁺ effectors at the graft site. In contrast, the majority of islet allografts transplanted into CD103^−/− hosts survived indefinitely. Transfer of wild-type CD8 cells into CD103^−/− hosts elicited prompt rejection of long-surviving islet allografts, whereas CD103^−/− CD8 cells were completely ineffectual, demonstrating that the defect resides at the level of the CD8 cell. CD8 cells in CD103^−/− hosts exhibited normal effector responses to donor alloantigens in vitro and trafficked normally to the graft site, but strikingly failed to infiltrate the islet allograft itself. These data establish a causal relationship between CD8⁺CD103⁺ effectors and destruction of graft epithelial elements and suggest that CD103 critically functions to promote intragraft migration of CD8 effectors into epithelial compartments.