Complete remission of tumors in mice with neoantigen-painted exosomes and anti-PD-1 therapy.

Neoantigen-based cancer vaccines are emerging as promising tumor therapies, but enhancement of immunogenicity can further improve therapeutic outcomes. Here, we demonstrate that anchoring different peptide neoantigens on subcutaneously administered serum exosomes promote lymph node homing and dendritic cell uptake, resulting in significantly enhanced antigenicity in vitro and in vivo. Exosomes anchoring of melanoma peptide neoantigens augmented the magnitude and breadth of T cell response in vitro and in vivo, to a greater extent with CD8(+) T cell responses. Simultaneous decoration of different peptide neoantigens on serum exosomes induced potent tumor suppression and neoantigen-specific immune responses in mice with melanoma and colon cancer. Complete tumor eradication and sustainable immunological memory were achieved with neoantigen-painted serum exosome vaccines in combination with programmed cell death protein 1 (PD-1) antibodies in mice with colon cancer. Importantly, human serum exosomes loaded with peptide neoantigens elicited significant tumor growth retardation and immune responses in human colon cancer 3-dimensional (3D) multicellular spheroids. Our study demonstrates that serum exosomes direct in vivo localization, increase dendritic cell uptake, and enhance the immunogenicity of antigenic peptides and thus provides a general delivery tool for peptide antigen-based personalized immunotherapy.