Interferon-gamma inhibits aldehyde dehydrogenase(bright) cancer stem cells in the 4T1 mouse model of breast cancer

BACKGROUND: Despite improvements in disease diagnosis, treatment, and prognosis, breast cancer is still a leading cause of cancer death for women. Compelling evidence suggests that targeting cancer stem cells (CSCs) have a crucial impact on overcoming the current shortcomings of chemotherapy and radiotherapy. In the present study, we aimed to study the effects of T cells and a critical anti-tumor cytokine, interferon-gamma (IFN-γ), on breast cancer stem cells. METHODS: BALB/c mice and BALB/c nude mice were subcutaneously injected with 4T1 tumor cells. Tumor growth and pulmonary metastasis were assessed. ALDEFLOUR™ assays were performed to identify aldehyde dehydrogenase(bright) (ALDH(br)) tumor cells. ALDH(br) cells as well as T cells from tumor-bearing BALB/c mice were analyzed using flow cytometry. The effects of CD8(+) T cells on ALDH(br) tumor cells were assessed in vitro and in vivo. The expression profiles of ALDH(br) and ALDH(dim) 4T1 tumor cells were determined. The levels of plasma IFN-γ were measured by enzyme-linked immunosorbent assay, and their associations with the percentages of ALDH(br) tumor cells were evaluated. The effects of IFN-γ on ALDH expression and the malignancy of 4T1 tumor cells were analyzed in vitro. RESULTS: There were fewer metastatic nodules in tumor-bearing BALB/c mice than those in tumor-bearing BALB/c nude mice (25.40 vs. 54.67, P < 0.050). CD8(+) T cells decreased the percentages of ALDH(br) 4T1 tumor cells in vitro (control vs. effector to target ratio of 1:1, 10.15% vs. 5.76%, P < 0.050) and in vivo (control vs. CD8(+) T cell depletion, 10.15% vs. 21.75%, P < 0.001). The functions of upregulated genes in ALDH(br) 4T1 tumor cells were enriched in the pathway of response to IFN-γ. The levels of plasma IFN-γ decreased gradually in tumor-bearing BALB/c mice, while the percentages of ALDH(br) tumor cells in primary tumors increased. IFN-γ at a concentration of 26.68 ng/mL decreased the percentages of ALDH(br) 4T1 tumor cells (22.88% vs. 9.88%, P < 0.050) and the protein levels of aldehyde dehydrogenase 1 family member A1 in 4T1 tumor cells (0.86 vs. 0.49, P < 0.050) and inhibited the abilities of sphere formation (sphere diameter <200 μm, 159.50 vs. 72.0; ≥200 μm, 127.0 vs. 59.0; both P < 0.050) and invasion (89.67 vs. 67.67, P < 0.001) of 4T1 tumor cells. CONCLUSION: CD8(+) T cells and IFN-γ decreased CSC numbers in a 4T1 mouse model of breast cancer. The application of IFN-γ may be a potential strategy for reducing CSCs in breast cancer.