Interleukin-15-armed trivalent mRNA vaccine elicits robust and durable protection against lethal mpox and vaccinia virus challenges in mice

The global re-emergence of mpox virus (MPXV) poses a critical threat, particularly to vulnerable immunocompromised populations, thus highlighting an urgent need for effective and safe interventions. In this study, we developed and compared three mRNA-LNP candidates: a trivalent cocktail of A35R, M1R, and A29L (Mixture), a fusion construct (A35R-M1R-A29L; AMA), and an IL-15-co-expressing fusion construct (AMA-IL-15). Among the three formulations, AMA-IL-15 elicited potent and durable neutralizing antibody responses, demonstrating long-lasting, broad-spectrum cross-protection against orthopoxviruses. It also induced potent antigen-specific T-cell responses and augmented T follicular helper (Tfh) and germinal center (GC) B-cell activity. These responses translated into faster pulmonary MPXV clearance, reduced early weight loss, and quicker recovery compared to the Mixture or AMA vaccines against lethal mpox or vaccinia virus challenge. In immunocompromised mice, AMA-IL-15 enhanced MPXV viral clearance, reduced viral DNA levels, and achieved complete survival. Moreover, the AMA-IL-15 mRNA candidate exhibited satisfactory safety outcomes. Together, AMA-IL-15 outperformed other formulations in immunogenicity and protective efficacy, supporting its potential as a promising next-generation mpox vaccine for high-risk populations during the ongoing global MPXV epidemic.