Association between primary graft function and 5-year outcomes of islet allogeneic transplantation in type 1 diabetes: a retrospective, multicentre, observational cohort study in 1210 patients from the Collaborative Islet Transplant Registry

Background: Allogeneic islet transplantation is a validated therapy in type 1 diabetes; however, there is decline of transplanted islet graft function over time and the mechanisms underlying this decline are unclear. We evaluated the distinct association between primary graft function (PGF) and 5-year islet transplantation outcomes. Methods: In this retrospective, multicentre, observational cohort study, we enrolled all patients from the Collaborative Islet Transplant Registry who received islet transplantation alone (ITA recipients) or islet-after-kidney transplantation (IAK recipients) between Jan 19, 1999, and July 17, 2020, with a calculable PGF (exposure of interest), measured 28 days after last islet infusion with a validated composite index of islet graft function (BETA-2 score). The primary outcome was cumulative incidence of unsuccessful islet transplantation, defined as an HbA1c of 7·0% (53 mmol/mol) or higher, or severe hypoglycaemia (ie, requiring third-party intervention to correct), or a fasting C-peptide concentration of less than 0·2 ng/mL. Secondary outcomes were graft exhaustion (fasting C-peptide <0·3 ng/mL); inadequate glucose control (HbA1c ≥7·0% [53 mmol/mol] or severe hypoglycaemia); and requirement for exogenous insulin therapy (≥14 consecutive days). Associations between PGF and islet transplantation outcomes were explored with a competing risk analysis adjusted for all covariates suspected or known to affect outcomes. A predictive model based on PGF was built and internally validated by using bootstraps resampling method. Findings: In 39 centres worldwide, we enrolled 1210 patients with a calculable PGF (of those without missing data, mean age 47 years [SD 10], 712 [59·5%] were female, and 865 (97·9%) were White), who received a median of 10·8 thousand islet-equivalents per kg of bodyweight (IQR 7·4-13·5). 986 (82·4%) were ITA recipients and 211 (17·6%) were IAK recipients. Of 1210 patients, 452 (37·4%) received a single islet infusion and 758 (62·6%) received multiple islet infusions. Mean PGF was 14·3 (SD 8·8). The 5-year cumulative incidence of unsuccessful islet transplantation was 70·7% (95% CI 67·2-73·9), and was inversely and linearly related to PGF, with an adjusted subhazard ratio (sHR) of 0·77 (95% CI 0·72-0·82) per 5-unit increase of BETA-2 score (p<0·0001). Secondary endpoints were similarly related to PGF. The model-adjusted median C-statistic values of PGF for predicting 5-year cumulative incidences of unsuccessful islet transplantation, graft exhaustion, inadequate glucose control, and exogenous insulin therapy were 0·70 (range 0·69-0·71), 0·76 (0·74-0·77), 0·65 (0·64-0·66), and 0·72 (0·71-0·73), respectively. Interpretation: This global multicentre study reports a linear and independent association between PGF and 5-year clinical outcomes of islet transplantation. The main study limitations are its retrospective design and the absence of analysis of complications. Funding: Public Health Service Research, National Institutes of Health, Juvenile Diabetes Research Foundation International, Agence National de la Recherche, Fondation de l'Avenir, and Fonds de Dotation Line Renaud-Loulou Gasté.