We designed CRISPR interference (CRISPRi) to block KLF2 binding to either sites, and showed that one (for KBS-1; Fig. 3E, Fig. S9F) decreased overall Mi/EGFP level (Fig. S8H, Fig. 3G), retarded regeneration of Mi/EGFPHigh cells from isolated Mi/EGFPLow cells (Fig. 3F), reduced binding of KLF2 to the promoter (Fig. S9E), diminished extracellular CCL28 and IGFBP2 levels (Fig. 3J), and blunted the chemotolerance of three different breast cancer cell lines (Fig. 3H) and xenograft tumor (Fig. 3I) against docetaxel. This evidence concerns the gene KLF2 and breast cancer.