OBJECTIVE: This study aims to utilize PEGylated poly (lactic-co-glycolic acid) (PLGA) nanoparticles as a delivery system for simultaneous administration of the BRAF peptide, a tumor-specific antigen, and imiquimod (IMQ). The objective is to stimulate dendritic cell (DC) maturation, activate macrophages, and facilitate antigen presentation in C57BL6 mice. METHODS: PEG-PLGA-IMQ-BRAF nanoparticles were synthesized using a PLGA-PEG-PLGA tri-block copolymer, BRAF, and IMQ. Characterization included size measurement and drug release profiling. Efficacy was assessed in inhibiting BPD6 melanoma cell growth and activating immature bone marrow DCs, T cells, macrophages, and splenocyte cells through MTT and ELISA assays. In vivo, therapeutic and immunogenic effects potential was evaluated, comparing it to IMQ + BRAF and PLGA-IMQ-BRAF nanoparticles in inhibiting subcutaneous BPD6 tumor growth. RESULTS: The results highlight the successful synthesis of PEG-PLGA-IMQ-BRAF nanoparticles (203 ± 11.1 nm), releasing 73.4% and 63.2% of IMQ and BARF, respectively, within the initial 48 h. In vitro, these nanoparticles demonstrated a 1.3-fold increase in potency against BPD6 cells, achieving ~ 2.8-fold enhanced cytotoxicity compared to PLGA-IMQ-BRAF. Moreover, PEG-PLGA-IMQ-BRAF exhibited a 1.3-fold increase in potency for enhancing IMQ cytotoxic effects and a 1.1- to ~ 2.4-fold increase in activating DCs, T cells, macrophages, and splenocyte cells compared to IMQ-BRAF and PLGA-IMQ-BRAF. In vivo, PEG-PLGA-IMQ-BRAF displayed a 1.3- to 7.5-fold increase in potency for inhibiting subcutaneous BPD6 tumor growth compared to the other formulations. CONCLUSIONS: The findings suggest that PEG-PLGA nanoparticles effectively promote DC maturation, T cell activation, and potentially macrophage activation. The study highlights the promising role of this nanocomposite in vaccine development.