PDCD1 and metastatic neoplasm: constructed a cRGD-targeted polymeric oncolytic peptide LTX-315 and CpG adjuvant to combine with an anti-programmed cell death-1 (PD-1) antibody system; this approach provided strong, long-term immunotherapy for mouse malignant B16F10 melanoma and established a novel class of durable immunotherapy for hard-to-target and metastatic tumors, including melanoma (53).