Therapeutic targeting of bleomycin‐induced pulmonary fibrosis by human bone marrow mesenchymal stem cell‐derived extracellular vesicles and/or pirfenidone: Impact of sex in mature adult mice

Background and Purpose Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease with limited therapeutic options. This study compared the therapeutic effects of bone marrow mesenchymal stem cell‐derived extracellular vesicles (BM‐MSC‐EVs) with an IPF treatment, pirfenidone (PFD), in mature adult mice with established pulmonary fibrosis. Experimental Approach Nine to 10‐month old male and female C57BL/6 mice received an intranasal instillation of bleomycin (BLM) or saline on Days 0 and 7. Sub‐groups of BLM‐injured mice (n = 10 per group) were left untreated until Day 21 (d21) or d28 post‐injury, or received an intranasal administration of BM‐MSC‐EVs (d21), once‐daily oral PFD treatment (d21 to d27), or both treatments combined. Measures of lung compliance, inflammation and fibrosis were assessed at d28. Key Results BLM‐injured male and female mice had increased lung inflammation and interstitial transforming growth factor (TGF‐ β 1), myofibroblast and extracellular matrix (ECM) accumulation, but reduced matrix metalloproteinase (MMP 9) activity and MMP9:TIMP‐1 ratios at d21. These end‐points were maintained at d28 in male mice but were resolved in female mice. BM‐MSC‐EVs alone or combined with PFD attenuated or significantly reduced the lung inflammation and fibrosis‐related end‐points in male mice and promoted lung MMP‐9 activity in both sexes. In comparison, PFD alone partially but significantly reduced fibrosis progression but did not affect MMP or TIMP levels. Conclusions and Implications BM‐MSC‐EVs exerted anti‐fibrotic effects in male mice, which were maintained with PFD co‐administration. Treatment outcomes remained inconclusive in female mice. These findings highlight how ageing and sex influence therapeutic responses of EV‐based therapies for IPF.