Single-cell profiling identifies a CD8bright CD244bright Natural Killer cell subset that reflects disease activity in HLA-A29-positive birdshot chorioretinopathy.

Birdshot chorioretinopathy uveitis (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 healthy 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 CD56dim CD16+ NK cells in BCR-UV compared to healthy controls and to other types of non-infectious uveitis. Ex vivo restimulation showed that NK cells from BCR-UV patients exhibit increased secretion of TNF-alpha, a cytokine considered central to the pathogenesis of BCR-UV. Unbiased transcriptomic characterization at single-cell resolution established that the expanded CD16+ (i.e., FCGR3A+) NK cells also 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 showed 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 correlated with a significant decrease in CD8bright CD244bright NK cells. In conclusion, there is an expansion of CD8bright CD244bright NK cells during active disease in BCR-UV patients which decrease upon successful systemic immunomodulatory treatment, suggesting that CD8bright/CD244bright NK cells may be a pro-inflammatory NK subset involved in the underlying disease mechanism.