Inhalable Nanovaccine Based on Bioengineered Bacteria‐Derived Membrane Vesicles Against Lung Metastasis

Abstract Lung metastases pose a challenge in cancer treatment due to the lung's vascular network and immunosuppressive microenvironment. Conventional subcutaneous vaccines typically fail to elicit localized immune responses at metastatic sites. To address this, an inhalable nanovaccine, BMVax (bacterial membrane‐based vaccine), is developed using bacterial membrane vesicles from engineered E. coli expressing ClyA‐OVA 257‐264 . Proteomics with retention of immunostimulatory membrane proteins, enabled efficient antigen co‐delivery. BMVax ensured antigen cross‐presentation (2.2‐fold increase compared to the antigen + BMV mixture), driving robust antigen‐specific T‐cell proliferation. Inhaling triggers strong immune responses in tracheobronchial lymph nodes, boosting germinal center B cells (≈5.8‐fold), follicular helper T cells (≈4.9‐fold), and mature dendritic cells (≈2.5‐fold), achieving 83.3% complete prevention of lung metastasis. In B16‐OVA lung metastasis model, inhaled BMVax demonstrates superior tumor suppression compared to subcutaneous administration. It induces doubling germinal center B cells and 2.9‐fold more follicular helper T cells in the lymph nodes, as well as 2.9‐fold more antigen‐specific T cells in lung tissue than subcutaneous immunization. Tumor‐infiltrating T cells exhibit enhanced cytotoxicity and proliferation, reinforcing its therapeutic advantage over subcutaneous immunization. These findings highlight BMVax's potential as an inhalable cancer vaccine, capable of inducing strong immune responses, to effectively combat lung metastatic malignancies.