TGFB1 and osteosarcoma: Moreover, exosomes derived from 549 LuT3 cells and osteosarcoma lung metastatic foci (HOS LuT3) cells displayed pronounced LAP-TGF-β1 expression (Fig. 3L), further corroborating the intimate association between elevated exosomal LAP-TGF-β1 loads in lung metastatic foci and tumor micro-metastatic foci dissemination within the lung.