Since CD44 is known to promote tumor initiation and metastasis in breast cancer (Liu et al., 2019), we first tested the role of CD81 in self-renewal in TNBC by assessing its impact on mammosphere formation, cell growth, and pluripotency-related genes and proteins after gene KO, which was generated as pooled populations with two CD81 gRNAs using the CRISPR-Cas9 approach (Figure 1—figure supplement 1C). Here, CD81 is linked to breast cancer.