PTPN22 and lymphopenia: We hypothesized that the expanded Foxp3+ CD4 T cells may be restraining lymphopenia-induced proliferation in the context of the PTPN22 KO and attempted to address this point by specific depletion of Treg using an anti-CD25 antibody, but were unsuccessful due to the poor depletion efficacy of this antibody (Supplementary Figure 2).