To determine whether clinical sensitivity to peanut allergen (as defined by the eliciting dose during food challenge) is directly associated with the relative frequency within a peanut-specific regulatory CD4+ CD45RA- T cell subset (based on expression of CTLA-4, FOXP3, SGMS-1, FANK-1 and other validated iTreg signature genes) before the DBPCFC or 6-8 weeks after the DBPCFC.