Modulation of Pulmonary Microbiota by Antibiotic or Probiotic Aerosol Therapy: A Strategy to Promote Immunosurveillance against Lung Metastases

Pulmonary immunological tolerance to inhaled particulates might create a permissive milieu for lung metastasis. Lung microbiota contribute to pulmonary tolerance; here, we explored whether its manipulation via antibiotic or probiotic aerosolization favors immune response against melanoma metastasis. In lungs of vancomycin/neomycin-aerosolized mice, a decrease in bacterial load was associated with reduced regulatory T cells and enhanced T cell and NK cell activation that paralleled a significant reduction of melanoma B16 lung metastases. Reduction of metastases also occurred in lungs transplanted with bacterial isolates from antibiotic-treated lungs. Aerosolized Lactobacillus rhamnosus strongly promoted immunity against B16 lung metastases as well. Furthermore, probiotics or antibiotics improved chemotherapy activity against advanced B16 metastases. Thus, we identify a role for lung microbiota in metastasis and show that its targeting via aerosolization is a therapy that can prevent metastases and enhance responses to chemotherapy. Le Noci et al. reveal that modulation of pulmonary microbiota by antibiotic or probiotic aerosolization decreases tumor growth in the lung. Antibiotic treatment induces a reduction of immunosuppressive cells in the lung, while probiotic administration promotes maturation of resident antigen-presenting cells.