Subunit vaccines generally exhibit favorable safety profiles but often induce insufficient immunogenicity, highlighting the need for effective adjuvants capable of stimulating both cellular and humoral immune responses. This study aimed to develop and immunologically evaluate a synthetic monophosphoryl lipid A (MPLA)-based emulsion adjuvant platform, termed QTP709. The QTP709 series consists of three emulsion-based formulations (QTP709-1, QTP709-2, and QTP709-3) designed to achieve high chemical purity and long-term physicochemical stability. All formulations maintained nanoscale particle size distributions with low polydispersity indices for at least two years under refrigerated storage conditions. Immunological evaluation in murine models demonstrated that QTP709-1 and QTP709-2 significantly enhanced antigen-specific CD4⁺ T cell responses, including the induction of polyfunctional CD4⁺ T cells co-expressing IFN-γ, TNF-α, and IL-2. In addition, these formulations promoted strong humoral immune responses characterized by increased IgG2c production and relatively balanced IgG1/IgG2c ratios compared with the Th2-biased responses induced by alum. Collectively, these results indicate that the QTP709 adjuvant platform provides excellent physicochemical stability and promotes Th1-oriented cellular immunity together with balanced antibody responses, supporting its potential as a promising vaccine adjuvant platform.