Modulation of the Immune System in Down Syndrome for Improved Outcomes and Neurodevelopment - 1

This protocol describes a phase 2, double-blind, randomized, placebo-controlled clinical trial for Janus kinase (JAK) inhibition in Down syndrome (DS). This trial will evaluate the safety and efficacy of a 6-month treatment with the JAK1/3 inhibitor tofacitinib (XELJANZ) in individuals ages 6-22 (inclusive) with DS. There will be two main arms for this study: a treatment arm and a placebo control arm. Participants will be randomized into the treatment or placebo arm. Those completing 6 months in the placebo arm may be eligible to participate in a cross-over, open-label extension arm to receive 6 months of tofacitinib treatment. Participants will be evaluated during a Screening visit to determine eligibility, complete a Baseline visit if eligible, and be monitored via safety clinical laboratories and in-person evaluations by study doctors at 1 month, 3 months (mid-point visit) and 6 months (endpoint visit). An interim analysis of safety will be completed by an independent Data and Safety Monitoring Board (DSMB) after 40 participants have completed 6 months of treatment or placebo (20 in each arm).