 This clinical trial will last 172 to 216 weeks. Participants will be randomly assigned to receive peanut SLIT or placebo SLIT. All participants will have an entry oral food challenge OFC. The treatment group will receive gradual dosing escalations of peanut SLIT and maintenance therapy over a 44-week period, followed by another OFC. Following the OFC, participants will be unblinded, and the placebo group will receive peanut SLIT escalated to a higher maximum dose than the first treatment group. Maintenance therapy will continue for both groups for more than 2 years. 