Immune checkpoints in a genetically engineered mouse model of spontaneous autoimmune uveitis.

Engineered mutant AireGW/+Lyn-/- C57BL/6 mice are a model of spontaneous autoimmunity in which 50% of mice develop highly destructive uveitis due to compromised central and peripheral T cell tolerance. The key retinal autoantigen in these mice is interphotoreceptor retinoid-binding protein (IRBP). The CD4+ T cells recognizing the dominant epitope of IRBP, called P2, from eye-draining lymph nodes of mice with or without uveitis and from the retinas of mice with uveitis, were characterized by single-cell RNA sequencing (scRNA-seq) and flow cytometry. Mice with uveitis had autoantigen-specific T cells in the eye-draining lymph node and in the retinas, exhibiting a range of activation states and a Th1 polarization, along with a small fraction of Tregs. Mice without uveitis had low numbers of P2-specific T cells in the eye-draining lymph nodes, and in most mice a substantial proportion of them were FoxP3+ Tregs. Transient depletion of Tregs by treatment of heathy AireGW/+Lyn-/- Foxp3DTR+/Y mice with diphtheria toxin resulted in rapid expansion of P2-specific CD4+ T cells in the eye-draining LN, and some of the Treg depleted mice went on to develop uveitis. Thus, development of inflammation in the retina was limited by a checkpoint in the eye-draining lymph nodes involving Tregs, and also apparently by an additional peripheral tolerogenic mechanism.