Cancer immunotherapy faces challenges in achieving durable antitumor immunity due to poor immunogenicity of tumor antigens and inadequate immune activation. In this study, we developed a self-assembling neoantigen nanoparticle vaccine (Neo-NV) integrating charge-modified Kirsten rat sarcoma viral oncogene homologue (KRAS) G12V-derived multi-epitope peptides with dual adjuvants—hydrophilic CpG oligonucleotides (ODNs) and hydrophobic R848. Neo-NV demonstrated enhanced antigen uptake by dendritic cells (DCs) in vitro, promoting DC maturation and M1 macrophage polarization, while stimulating robust neoantigen-specific CD8⁺ T cell responses. Additionally, Neo-NV enhanced the activation of antigen-specific T cells from human peripheral blood mononuclear cells (PBMCs) and their proliferation in immunodeficient NSG mice. Moreover, it significantly increased CD4⁺ and CD8⁺ T cell proliferation in the spleen and PBMCs of mice, while promoting the activation and aggregation of CD4⁺ and CD8⁺ T cells in the draining lymph nodes. In murine KRAS G12V melanoma models, Neo-NV significantly suppressed tumor growth and prolonged survival without systemic toxicity, as evidenced by stable body weight and normal hepatic/renal biomarkers. Mechanistically, Neo-NV enhanced tumor-infiltrating lymphocyte (TIL) activation and memory precursor T cell formation. This study establishes Neo-NV as a modular platform for personalized immunotherapy, highlighting the synergy of dual adjuvants and self-assembled nanoparticle in overcoming neoantigen immunogenicity barriers.