Fig. 1: BCSC secretome compresses the stem cell pool size.

a FACS analysis of the proportion of ALDH+ or ALDH− cells after the growth of FACS-sorted ALDH+ or ALDH− T47D cells. b FACS analysis of the proportion of ALDH+ BCSCs in the RFP-labeled T47D cells co-cultured with the unlabeled ALDH−, ALDH+ or parental T47D cells. c FACS analysis of the proportion of ALDH+ BCSCs in the T47D cells cultured with the CM derived from ALDH+, ALDH−, or parental cells. d The schematic of conditioned medium and transwell co-culture system. e, f MCF-7 or T47D cells were co-cultured with mammosphere-enriched BCSCs or parental cells for 48 h, and the stemness properties were subsequently analyzed by ALDEFLUOR assay (e) or mammosphere-formation assay (f). Scale bars: 500 μm. g, h MCF-7 or T47D cells were cultured with the respective CM derived from mammosphere-enriched BCSCs or parental cells for 48 h, and the stemness properties were subsequently analyzed by ALDEFLUOR assay (g) or mammosphere-formation assay (h). Scale bars: 500 μm. i The schematic of co-implantation model. j, k A series of limiting diluted MCF-7-luc cells were co-implanted with unlabeled 4 × 10⁵ mammosphere-enriched BCSCs or parental cells into host mice. Bioluminescent imaging (BLI) was performed on tumors generated by MCF-7-luc cells (j), the CSC frequency was calculated using ELDA software (k). Results are shown as mean ± S.D. *P < 0.05; **P < 0.01; ***P < 0.001; ns not significant (One-way ANOVA followed by Tukey’s multiple comparison test in (b, c) others unpaired two-tailed Student’s t test). Source data are provided as a Source Data file.