TNFSF9 and cancer: Building on the successful transfection of B16F10 cancer cells with LNP/pOX40L and LNP/p4-1BBL in vitro, we further confirmed that OX40L and 4-1BBL were expressed in tumor cells following intratumoral injection of LNP/pOX40L and LNP/p4-1BBL, respectively, as determined by flow cytometry analysis (Figure S1).