Acute respiratory distress syndrome (ARDS) is an acute inflammatory lung injury characterized by increased alveolar-capillary permeability, noncardiogenic pulmonary edema, impaired gas exchange, and reduced lung compliance. MSC and extracellular-vesicle research has focused on immunomodulation, epithelial and endothelial barrier support, antimicrobial signaling, alveolar-fluid clearance, and modulation of secondary injury rather than direct replacement of the injured lung. Early clinical studies have primarily evaluated feasibility and safety, with heterogeneous products, doses, timing, and patient populations. No MSC or EV product is established as routine ARDS therapy. Lung-protective ventilation, treatment of the precipitating cause, appropriate fluid strategy, prone positioning when indicated, and other evidence-based critical care remain foundational.
Figure 1 placeholder — Acute respiratory distress syndrome
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD) is a heterogeneous chronic disorder characterized by persistent airflow limitation, airway inflammation, emphysema, chronic bronchitis phenotypes, and variable systemic effects. MSC and EV studies have proposed anti-inflammatory, immunomodulatory, endothelial, and tissue-supportive mechanisms. Small human studies have generally not established durable improvement in airflow obstruction or a class-wide reduction in exacerbations. Structural destruction of emphysematous lung should not be described as regenerated because inflammatory biomarkers or symptoms change. Smoking cessation, vaccination, inhaled pharmacotherapy, pulmonary rehabilitation, oxygen when indicated, and selected procedural or surgical approaches remain standard care.
Figure 2 placeholder — Chronic obstructive pulmonary disease
Pulmonary fibrosis
Pulmonary fibrosis encompasses disorders in which abnormal repair produces excessive extracellular-matrix deposition, distortion of lung architecture, and impaired gas exchange. Idiopathic pulmonary fibrosis is a major example, but fibrotic lung disease is etiologically diverse. MSC and EV research has explored antifibrotic signaling, modulation of fibroblast and myofibroblast activity, inflammatory pathways, epithelial injury, and matrix remodeling. Preclinical findings do not establish reversal of established human fibrosis. Small clinical studies cannot substitute for endpoints such as lung-function decline, exercise capacity, hospitalization, transplantation, or survival. Antifibrotic and disease-specific standard therapies should remain distinct from investigational regenerative approaches.
Figure 3 placeholder — Pulmonary fibrosis
Bronchopulmonary dysplasia
Bronchopulmonary dysplasia (BPD) is a chronic lung disease of prematurity involving disrupted alveolar and vascular development after immature lungs are exposed to oxygen, ventilation, inflammation, infection, and other injuries. Perinatal MSC and EV research has focused on paracrine support of alveolarization, vascular development, immunomodulation, and reduction of secondary injury. Early-phase neonatal studies have explored intratracheal or systemic cell administration, but developmental stage, gestational age, product, dose, timing, respiratory support, and long-term neurodevelopment all affect interpretation. Any pediatric or neonatal intervention requires especially stringent manufacturing, safety, consent, and long-term developmental surveillance.
Figure 4 placeholder — Bronchopulmonary dysplasia
Pulmonary hypertension
Pulmonary hypertension is a hemodynamic condition defined by elevated pulmonary arterial pressure and can arise from multiple disease groups with very different causes and treatments. Pulmonary arterial hypertension includes vascular remodeling, endothelial dysfunction, vasoconstriction, inflammation, and right-ventricular stress. MSC and EV research has investigated endothelial repair, angiogenic balance, inflammatory signaling, and vascular remodeling, predominantly in preclinical models. A favorable change in pulmonary vascular biology does not establish reduced pulmonary vascular resistance, improved exercise capacity, delayed clinical worsening, or survival. Approved disease-specific pulmonary-hypertension therapies and management of the underlying cause remain the appropriate standard comparator. The right ventricle must pump against this increased pulmonary vascular load and can ultimately fail.
Figure 5 placeholder — Pulmonary hypertension
Postinfectious lung injury
Postinfectious lung injury can follow severe viral, bacterial, or other pulmonary infection and may include persistent inflammation, organizing injury, impaired diffusion, vascular abnormalities, airway disease, or fibrosis. It is not one uniform diagnosis. MSC and EV research expanded during severe viral pneumonias because of proposed immunomodulatory and barrier-supportive effects, but study quality, product heterogeneity, evolving background care, and changing viral variants complicate interpretation. Improvement after infection can also reflect natural recovery. Persistent symptoms require diagnosis-specific evaluation; investigational cell or EV treatment should not be presented as proven treatment for nonspecific 'long-lung' or postinfectious syndromes.
Figure 6 placeholder — Postinfectious lung injury
Clinical takeaway
Pulmonary indications differ in mechanism, acuity, developmental context, and standard care. No class-wide MSC/EV efficacy conclusion is defensible across ARDS, COPD, fibrosis, BPD, pulmonary hypertension, and postinfectious injury.
Biological rationale
Proposed mechanisms include immunomodulation, alveolar epithelial and endothelial support, barrier stabilization, alveolar-fluid clearance, antifibrotic signaling, angiogenic balance, and modulation of host repair.
Product identity
Autologous and allogeneic MSCs from different tissues, culture-expanded products, conditioned media, and EV preparations are biologically and manufacturing-wise distinct.
Preclinical evidence
Animal and ex-vivo lung models support multiple protective mechanisms, but injury models, developmental stage, dose, timing, and respiratory support may differ substantially from human disease.
Human clinical evidence
Human development remains uneven and generally investigational. Early trials often emphasize safety and feasibility and are limited by small samples, heterogeneous syndromes, changing standard care, and surrogate outcomes.
Trial design
Pulmonary trials should distinguish acute from chronic disease, define etiology and severity, account for ventilatory support and background therapy, and prioritize validated physiologic and patient-important outcomes.
Dose and administration
Intravenous and intratracheal cell delivery and inhaled or airway-directed biologic strategies create different biodistribution, retention, dosing, and safety profiles.
Safety
Potential concerns include infusion reactions, thrombo-inflammatory interactions, infection, immune effects, airway complications with local delivery, and uncertainty about long-term effects in developing lungs.
Regulatory status
Regulatory status is specific to the exact product, indication, route, age group, jurisdiction, and date. Emergency or trial use does not imply routine authorization.
Standard care
Evidence-based critical care for ARDS, inhaled and rehabilitative COPD care, antifibrotic or disease-specific treatment, neonatal respiratory care, and approved pulmonary-hypertension therapies remain central.
Knowledge gaps
Key gaps include validated potency assays, optimal route and dose, treatment timing, disease phenotyping, long-term safety, developmental outcomes, and durable clinical benefit.
Bottom-line evidence statement
Pulmonary MSC and EV approaches remain investigational; mechanistic and early-phase signals must not be converted into claims of restored lung architecture or proven clinical benefit.
Additional controlled terminology
An alveolus is the gas-exchanging airspace lined by alveolar epithelium and closely associated with pulmonary endothelium; together they form the alveolar-capillary barrier. Injury can produce pulmonary edema, impaired gas exchange, reduced lung compliance, and defective alveolar-fluid clearance. Emphysema contributes to airflow limitation. Fibrosis involves extracellular matrix produced and remodeled by fibroblast and myofibroblast populations. Alveolarization is especially important in prematurity and BPD. Pulmonary vascular resistance and right-ventricle load are central in pulmonary arterial hypertension and vascular remodeling. Organizing pneumonia is one possible postinfectious pattern, while diffusing capacity assesses gas-transfer function. Lung-protective ventilation and prone positioning are established ARDS strategies, and pulmonary rehabilitation is established in appropriate chronic lung disease.