Juhi R. Kuchroo

Inhibitory signals through the PD-1 pathway regulate T cell activation, T cell tolerance, and T cell exhaustion. Studies of PD-1 function have focused primarily on effector T cells. Far less is known about PD-1 function in regulatory T (T reg) cells. To study the role of PD-1 in T reg cells, we generated mice that selectively lack PD-1 in T reg cells. PD-1-deficient T reg cells exhibit an activated phenotype and enhanced immunosuppressive function. The in vivo significance of the potent suppressive capacity of PD-1-deficient T reg cells is illustrated by ameliorated experimental autoimmune encephalomyelitis (EAE) and protection from diabetes in nonobese diabetic (NOD) mice lacking PD-1 selectively in T reg cells. We identified reduced signaling through the PI3K-AKT pathway as a mechanism underlying the enhanced suppressive capacity of PD-1-deficient T reg cells. Our findings demonstrate that cell-intrinsic PD-1 restraint of T reg cells is a significant mechanism by which PD-1 inhibitory signals regulate T cell tolerance and autoimmunity.

Multiple sclerosis (MS) is an inflammatory disease of the CNS white matter associated with T cell infiltrates and alterations of immune functions that can be measured in the peripheral immune system. TIM-3 has been identified as a central regulator of IFN-gamma-secreting type 1 Th (Th1) cells and immune tolerance. In this study, using a newly generated mAb against human TIM-3, we examined TIM-3 function on ex vivo CD4(+) T cells isolated from the circulation of healthy subjects and patients with MS. Blocking TIM-3 during T cell stimulation significantly enhanced IFN-gamma secretion in control subjects but had no effect in untreated patients with MS, demonstrating a defect in TIM-3 immunoregulation. Treatment with glatiramer acetate or IFN-beta reversed this functional defect. Reduced levels and altered kinetics of T cell TIM-3 expression, which was restored in treated patients, is one mechanism that can explain the loss of TIM-3 regulation of T cell function in untreated patients with MS. These data provide functional, mechanistic data for dysregulated TIM-3 immunoregulation in a human autoimmune disease and suggest that approved therapies for the treatment of MS may function in part by restoring TIM-3 immunoregulation of T cell function.

The ability to monitor anti-tumor CD8+ T cell responses in the blood has tremendous therapeutic potential. Here, we used paired single-cell RNA and TCR sequencing to detect and characterize "tumor-matching" (TM) CD8+ T cells in the blood of mice with MC38 tumors or melanoma patients using the TCR as a molecular barcode. TM cells showed increased activation compared with nonmatching T cells in blood and were less exhausted than matching cells in tumors. Importantly, PD-1, which has been used to identify putative circulating anti-tumor CD8+ T cells, showed poor sensitivity for identifying TM cells. By leveraging the transcriptome, we identified candidate cell surface markers for TM cells in mice and patients and validated NKG2D, CD39, and CX3CR1 in mice. These data show that the TCR can be used to identify tumor-relevant cells for characterization, reveal unique transcriptional properties of TM cells, and develop marker panels for tracking and analysis of these cells.