The Ubiquitin Ligase Adaptor NDFIP1 Selectively Enforces a CD8⁺ T Cell Tolerance Checkpoint to High-Dose Antigen

Escape from peripheral tolerance checkpoints that control cytotoxic CD8⁺ T cells is important for cancer immunotherapy and autoimmunity, but pathways enforcing these checkpoints are mostly uncharted. We reveal that the HECT-type ubiquitin ligase activator, NDFIP1, enforces a cell-intrinsic CD8⁺ T cell checkpoint that desensitizes TCR signaling during in vivo exposure to high antigen levels. Ndfip1-deficient OT-I CD8⁺ T cells responding to high exogenous tolerogenic antigen doses that normally induce anergy aberrantly expanded and differentiated into effector cells that could precipitate autoimmune diabetes in RIP-OVA^hi mice. In contrast, NDFIP1 was dispensable for peripheral deletion to low-dose exogenous or pancreatic islet-derived antigen and had little impact upon effector responses to Listeria or acute LCMV infection. These data provide evidence that NDFIP1 mediates a CD8⁺ T cell tolerance checkpoint, with a different mechanism to CD4⁺ T cells, and indicates that CD8⁺ T cell deletion and anergy are molecularly separable checkpoints.