We will perform a partial phase I and a complete phase II/III clinical trial of ustekinumab for the prevention and treatment of type 1 diabetes (T1D). Animal and human studies have strongly implicated both the IL-17 and IFN-gamma pathways in the pathogenesis of beta cell destruction. We hypothesize that the ustekinumab, a humanized monoclonal antibody that blocks the the p40 subunit shared between IL-12 and IL-23, will inhibit these two pathways and thus abrogate beta cell destruction. We further hypothesize that if ustekinumab therapy is started shortly after presentation of disease, sufficient beta cells will be rescued and regenerated to preserve physiological insulin secretion by the pancreas. We will initially conduct an open-label safety and dosing assessment study with 9 adult (18-30 years of age) subjects randomized to three different dosing regimens. The main endpoints will be safety and immunological assessment of inhibition of the IL-17 and IFN-gamma pathways. Following and informed by the pilot study, we will immediately begin a phase II/III double-blind, placebo controlled efficacy trial. The main endpoint of this study will be the C-peptide secretion after a mixed meal tolerance test (MMTT) at 1 year after the first dose is given. We will compare treatment with ustekinumab to placebo to determine if the drug has efficacy in T1D.