To investigate whether DKK1 suppresses human NK cells (hNK), we isolated hNK cells from healthy donor PBMCs (Fig. 8A) and found that recombinant human DKK1 (rhDKK1) significantly decreased hNK cell cytotoxicity against the MDA-MB-231 TNBC cell line (Fig. 8B), the T47D ER+ breast cancer cell line (Fig. 8C) and the NK-sensitive K562 cell line (Fig. 8D). This evidence concerns the gene DKK1 and breast cancer.