We also deleted Apex1 in MRL/Mplpr/lpr (Lpr) mice, which are known to develop systemic lupus–like disease involving abnormal activation of Tfh cells (22), and found that deletion of Apex1 (Lpr-Apex1fl/flCd4Cre) completely inhibited the lupus phenotype (Supplemental Figure 3A). Here, APEX1 is linked to systemic lupus erythematosus.