NKX6.1 mRNA copy number is an actionable biomarker associated with islet function and clinical outcomes after islet transplantation

Islet transplantation, a validated therapy for type 1 diabetes, shows heterogeneous clinical outcomes. There is an unmet need for actionable biomarkers predicting islet graft potency before transplantation. We leveraged a comprehensive set of clinical data and islet samples to explore the relation between islet NKX6.1 gene expression and clinical transplantation outcomes. We measured NKX6.1 copy number with digital PCR in 114 clinical islet preparations and showed its linear correlation with islet graft function in a mouse bioassay, independently of islet mass, purity, and viability ( P < 0.01). Analyzing the clinical outcomes of 34 patients who received two or three islet preparations, we showed the added value of total NKX6.1 copy number to predict primary graft function, as compared with islet mass alone (Delong test, P < 0.001). Using a multiple regression Cox model, adjusted for islet mass, purity, and viability, a high total NKX6.1 copy number was independently correlated with 10-year survival of islet graft success [adjusted hazard ratio (HR) [95% CI]: 0.63 [0.43; 0.92], P < 0.017] and insulin independence (HR [95% CI]: 0.70 [0.52; 93], P < 0.01). This relation was confirmed in an independent cohort of nine patients receiving a single islet transplantation in other centers. Genetic silencing with anti- NKX6.1 shRNA or pharmacological induction of NKX6.1 with silymarin in vitro indicated a causal link between NKX6.1 gene expression and islet graft function. These results suggest that NKX6.1 mRNA expression can predict islet graft function and may serve as an actionable biomarker of graft potency in β cell replacement.