The lung is a major site of metastasis associated with poor clinical outcomes and a tumor immune microenvironment that represents an attractive but challenging therapeutic target.

We investigated a lung-targeted immunotherapeutic approach using intravenously administered cationic mRNA-lipoplexes (RNA-LPX) encoding interferon-α, interleukin-7 and a CD25-binding–reduced interleukin-2 variant. Anti-tumor efficacy was evaluated in murine metastasis models. Immune responses were assessed by flow cytometry, functional assays and single-cell RNA sequencing of CD45⁺ immune cells from lung metastases. Translational relevance was explored using primary human tumor cultures.

Treatment induced a potent anti-tumor response and prolonged survival, including in models of T cell escape. Increased activation, proliferation and effector function of CD8⁺ T cells and natural killer (NK) cells were observed, accompanied by reduced regulatory T cell abundance and activity. Single-cell RNA sequencing further defined immune remodeling, revealing expansion of cytotoxic CD8⁺ T cell states and proliferating, metabolically active NK cell subsets that emerged as a major source of granzyme B. Trajectory analysis indicated progressive NK cell maturation toward activated states, while type I interferon response programs were induced across immune populations. No marked induction of exhaustion-associated markers was observed. Functional depletion experiments confirmed that both CD8⁺ T cells and NK cells contribute to anti-tumor efficacy, with NK cells compensating in models of MHC-I loss.

Lung-targeted RNA-encoded cytokines induce coordinated innate and adaptive immune responses and provide a mechanistic and translational framework for treating metastatic lung disease.

We thank all members of the TRON and BioNTech teams for technical and experimental support. This work was supported by the Federal Ministry of Education and Research (BMBF, grant 13N13340).