ALDH1A1 and cancer: In keeping with these results, we also identified a close contact between ALDH1A1-positive malignant cells and CD3- (Fig. 6a, b) or PD1-expressing (Fig. 6a, b) T cells in human TNBCs in situ, which further indicates the capability of the CSCs to directly interact with T cells and thus potentially influence the immune response to cancer.