The impact of islet mass, number of transplants, and time between transplants on graft function in a national islet transplant program by Forbes, S, Flatt, AJ, Bennett, D, Crookston, R, Pimkova, M, Birtles, L, Pernet, A, Wood, RC, Burling, K, Barker, P, Counter, C, Lumb, A, Choudhary, P, Rutter, MK, Rosenthal, M, Sutherland, A, Casey, J, Johnson, P, Shaw, JAM