Single-cell profiling identifies Natural Killer cell subset that reflects disease activity in HLA-A29-positive birdshot uveitis

Birdshot chorioretinopathy (BCR-UV) is strongly associated with HLA-A29 which implicates MHC-I pathway mediated perturbation of natural killer (NK) cells as a potential disease mechanism. We profiled blood NK cells at single-cell resolution in a cohort of patients and controls and investigated the links between NK cell subpopulations and disease activity. Flow cytometry analysis of major immune cell lineages revealed substantial expansion of the CD16-positive NK cells in BCR-UV compared to controls, and other types of non-infectious uveitis. Ex vivo culture revealed that NK cells from patients exhibit increased secretion of TNF-alpha, a cytokine driving eye inflammation in BCR-UV. Unbiased transcriptomic characterization at single-cell resolution established that the expanded CD16+ (i.e., FCGR3A+) NK cells co-express high levels of CD8A and CD244, indicating expansion of a subset of CD56dim CD16+ CD8+ NK cells in patients. Confirmation of these results by high-dimensional flow cytometry further substantiated that the BCR-UV-associated CD8bright CD244bright NK cells displayed activation receptors including CD314 (NKG2D), and cytotoxicity receptor CD337 (NKp30). Finally, longitudinal monitoring of patients showed that clinical remission after systemic immunomodulatory treatment correlates with a significant decrease in CD8bright CD244bright NK cells. In conclusion, an activated CD8+CD244+ NK subpopulation is expanded in patients with BCR-UV and correlates with systemic treatment response.