In this study, synthetic vaccine nanoparticles (SVNPs) that efficiently targeted lymph nodes, where immune responses against foreign antigens are primed, were developed to enhance antitumor immunity. The size (20-70 nm) and surface character (amination) of poly(gamma-glutamic acid)-based SVNPs were selected for effective loading and delivery (i.e., migration and retention) of model tumor antigen (OVA) and toll-like receptor 3 agonist (poly (I:C)) to immune cells in lymph nodes. Antigen-presenting cells treated with SVNP-OVA and SVNP-IC showed higher uptake of OVA and poly (I: C) and higher secretion of inflammatory cytokines (TNF-alpha, IL-6) and type I interferon (IFN-alpha, IFN-beta) than those treated with OVA and poly (I: C) alone. In vivo analysis revealed higher levels of activation markers, inflammatory cytokines, and type I IFNs in the lymph nodes of mice immunized with SVNP-IC compared to those of mice in other groups. SVNP-IC-treated mice showed significantly greater in vivo natural killer cell expansion/activation (NK1.1(+) cells) and CD8(+) T cell response (CD8(+) INF-gamma(+) cells) in innate and adaptive immunity, respectively. Both preventive and therapeutic vaccination of EG7-OVA tumor-bearing mice using the simultaneous injection of both SVNP-OVA and SVNP-IC induced higher antitumor immunity and inhibited tumor growth. (C) 2017 Elsevier Ltd. All rights reserved.