To further determine whether systemic delivery of miR-21–3p by gold nanoparticle holds in vivo therapeutic potential to synergize with anti-PD-1 immunotherapy, the preclinical mice model established via the subcutaneous injection of B16F10 melanoma cells into the flank of C57BL/6 mice was employed, and anti-PD-1 antibody and miR-21–3p-loaded AuNp were both injected intraperitoneally as indicated (online supplemental figure S3B). Here, PDCD1 is linked to melanoma.