Interleukin 2 (IL2) is a crucial cytokine in T-cell immunity, with a promising potential in cancer vaccines. However, therapeutic application of IL2 is hampered by its short half-life and substantial toxicity. This study reports preclinical characterization of a mouse serum albumin–IL2 fusion protein (Alb–IL2) encoded on nucleoside-modified RNA that is delivered via a nanoparticle formulation (Alb–IL2 RNA-NP) mediating prolonged cytokine availability. Alb–IL2 RNA-NP was combined with RNA-lipoplex (RNA-LPX) vaccines to evaluate its effect on the expansion of vaccine-induced antigen specific T-cell immunity. In mice dosed with Alb–IL2 RNA-NP, translated protein was shown to be systemically available up to 2 days, with an albumin-dependent preferred presence in the tumor and tumor-draining lymph node. Alb–IL2 RNA-NP administration prolonged serum availability of the cytokine compared with murine recombinant IL2. In combination with RNA-LPX vaccines, Alb-IL2 RNA-NP administration highly increased the expansion of RNA-LPX vaccine–induced CD8+ T cells in the spleen and blood. The combination enhanced and sustained the fraction of IL2 receptor (IL2R) α-positive antigen-specific CD8+ T cells and ameliorated the functional capacity of the CD8+ T-cell population. Alb–IL2 RNA-NP strongly improved the antitumor activity and survival of concomitant RNA-LPX vaccination and PD-L1 blockade in a subcutaneous mouse tumor model. The favorable pharmacokinetic properties of Alb–IL2 RNA-NP render it an attractive modality for rationally designed combination immunotherapy. RNA vaccines that induce tumor-specific T-cell immunity for Alb–IL2 RNA-NP to further amplify are particularly attractive combination partners.

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