SMAD5 and breast cancer: In summary, our study revealed infiltrating CD73+γδ1 T cells as a key immunosuppressive component in the BC microenvironment, and we speculated that BCC-derived exosomal SNHG16 promotes the activation of the TGF-β1/SMAD5 pathway by sponging miR-16–5p and results in the conversion of γδ1 T cells into the CD73+ immunosuppressive subtype.