Phase II multicentre, double-blind, randomised trial of ustekinumab in adolescents with new-onset type 1 diabetes (USTEK1D): trial protocol by Gregory, JW, Carter, K, Cheung, WY, Holland, G, Bowen-Morris, J, Luzio, S, Dunseath, G, Tree, T, Yang, JHM, Marwaha, A, Ali, MA, Bashir, N, Hutchings, HA, Fegan, GW, Stenson, R, Hiles, S, Marques-Jones, S, Brown, A, Tatovic, D, Dayan, C