Exosome Treatment of Bronchopulmonary Dysplasia: How Pure Should Your Exosome Preparation Be?

We read with interest the article by Willis and colleagues (1) about the striking therapeutic efficacy of exosomes isolated from mesenchymal stem cells (MSCs) in a mouse model of bronchopulmonary dysplasia (BPD). BPD is a multifactorial, chronic lung disease that occurs in 40–45% of infants born at <29 weeks of gestation and is associated with significant long-term pulmonary morbidities. Because no effective treatment is available, there is an urgent need for novel therapies capable of reversing the course of the disease. Pioneering work done by Hansmann and colleagues (2) demonstrated that the intravenous administration of MSCs or MSC-conditioned medium (MSC-CM) reduced lung injury and inflammation, and prevented pulmonary hypertension in an animal model of hyperoxia-induced BPD. These results were confirmed by other groups, and we obtained similar results after administering human amniotic fluid cells (3). Lee and colleagues (4) subsequently showed that the exosome-enriched fraction of MSC-CM was therapeutically active, paving the way for the use of these biological nanoparticles in the treatment of BPD. Exosomes are membrane vesicles that convey a variety of metabolic signals between cells, and clinical-grade exosomes can be produced for use in therapeutic applications, with considerable advantages over living cells in terms of safety, applicability, and cost (5).