Stem cell therapy for bronchopulmonary dysplasia: bench to bedside translation

Stem cells for neonatal brain injury - Lessons from the bench

Neonatal brain injury resulting from various intractable disorders including intraventricular hemorrhage and hypoxic ischemic encephalopathy still remains a major cause of mortality and morbidities with few effective treatments. Recent preclinical research results showing the pleiotropic neuroprotective effects of stem cell therapy, specifically mesenchymal stem cells (MSCs), suggest that MSCs transplantation might be a promising new therapeutic modality for neuroprotection against the currently intractable and devastating neonatal brain injury with complex multifactorial etiology. This review summarizes recent advances in preclinical stem cell research for treating neonatal brain injury with a focus on the important issues including the mechanism of neuroprotection, and determining the ideal cell source, route, timing and dose of MSCs transplantation.

Stem cell derived exosomes-based therapy for acute lung injury and acute respiratory distress syndrome: A novel therapeutic strategy

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a common critical disease which can be caused by multiple pathological factors in clinic. However, feasible and effective treatment strategies of ALI/ARDS are limited. At present, the beneficial effect of stem cells (SCs)-based therapeutic strategies for ALI/ARDS can be attributed to paracrine. Exosomes, as a paracrine product, are regarded as a critical regulatory mediator. Furthermore, substantial evidence has indicated that exosomes from SCs can transmit bioactive components including genetic material and protein to the recipient cells and provide a protective effect. The protective role is played through a series of process including inflammation modulation, the reconstruction of alveolar epithelium and endothelium, and pulmonary fibrosis prevention. Therefore, SCs derived exosomes have the potential to be used for therapeutic strategies for ALI/ARDS. In this review, we discuss the present understanding of SCs derived exosomes related to ALI/ARDS and provide insights for developing a cell-free strategy for treating ALI/ARDS.

Variations in Umbilical Cord Hematopoietic and Mesenchymal Stem Cells With Bronchopulmonary Dysplasia

Objective: To test the hypothesis that umbilical cord blood-derived CD34+ hematopoietic stem cells (HPSC), cord tissue-derived CD90+ and CD105+ mesenchymal stem cells (MSC) vary with bronchopulmonary dysplasia (BPD). Methods: We conducted a prospective longitudinal study at a large birth center (Prentice Women's Hospital in Chicago, IL). Premature infants (N = 200) were enrolled in 2:1:1 ratio based on gestational age (GA): mildly preterm (31-32 weeks), moderately preterm (29-30 weeks), and extremely preterm (23-28 weeks). Cord blood (CB) and cord tissues (CT) were collected at birth using commercial banking kits, and analyzed for collection blood volume, tissue mass, CD34+, CD90+, CD105+ counts, and concentrations. Multiplex immunoassay was used to measure 12 cytokines and growth factors in CB plasma of 74 patients. BPD severity was defined according to NIH consensus definitions. Univariate and multivariate regression models were used to identify perinatal covariates and assess associations between stem cell concentrations, cytokines, and BPD outcomes. Results: Of 200 patients enrolled (mean GA = 30 ± 2 weeks), 30 developed mild, 24 moderate, and 19 severe BPD. Concentrations of HPSC and MSC, as measured by %CD34+, %CD90+, and %CD105+ of total cells, increased with degree of prematurity. Collection parameters varied with GA, birth weight (BW), gender, prolonged rupture of membranes, mode of delivery, chorioamnionitis, and multiple gestation. Moderate-severe BPD or death was increased with lower GA, BW, Apgar scores, and documented delayed cord clamping. %CD34+ and %CD90+ were increased with BPD and directly correlated with BPD severity. Severe BPD was positively associated with %CD34+ (beta-coefficient = 0.9; 95% CI = 0.4-1.5; P < 0.01) and %CD90+ (beta-coefficient = 0.4; 95% CI = 0.2-0.6; P < 0.001) after adjustment for covariates. CB plasma granulocyte-colony stimulating factor (G-CSF) was inversely associated with %CD90+, and decreased with BPD. Below median G-CSF combined with elevated %CD90+ predicted BPD (positive predictive value = 100%). Conclusions: CB and CT collections yielded high concentrations of HPSCs and MSCs in BPD infants, accompanied by low circulating G-CSF. These variations suggest possible mechanisms by which stem cell differentiation and function predict BPD.

Human Mesenchymal Stem Cell Therapy Reverses Su5416/Hypoxia-Induced Pulmonary Arterial Hypertension in Mice

Aims: Pulmonary arterial hypertension (PAH) is a disease characterized by an increase in pulmonary vascular resistance and right ventricular (RV) failure. We aimed to determine the effects of human mesenchymal stem cell (hMSC) therapy in a SU5416/hypoxia (SuH) mice model of PAH. Methods and Results: C57BL/6 mice (20-25 g) were exposure to 4 weeks of hypoxia combined vascular endothelial growth factor receptor antagonism (20 mg/kg SU5416; weekly s.c. injections; PAH mice). Control mice were housed in room air. Following 2 weeks of SuH exposure, we injected 5 × 10⁵ hMSCs cells suspended in 50 μL of vehicle (0.6 U/mL DNaseI in PBS) through intravenous injection in the caudal vein. PAH mice were treated only with vehicle. Ratio between pulmonary artery acceleration time and RV ejection time (PAAT/RVET), measure by echocardiography, was significantly reduced in the PAH mice, compared with controls, and therapy with hMSCs normalized this. Significant muscularization of the PA was observed in the PAH mice and hMSC reduced the number of fully muscularized vessels. RV free wall thickness was higher in PAH animals than in the controls, and a single injection of hMSCs reversed RV hypertrophy. Levels of markers of exacerbated apoptosis, tissue inflammation and damage, cell proliferation and oxidative stress were significantly greater in both lungs and RV tissues from PAH group, compared to controls. hMSC injection in PAH animals normalized the expression of these molecules which are involved with PAH and RV dysfunction development and the state of chronicity. Conclusion: These results indicate that hMSCs therapy represents a novel strategy for the treatment of PAH in the future.

Serious adverse events of cell therapy for respiratory diseases: a systematic review and meta-analysis

Background

Cell therapy holds the most promising for acute and chronic deleterious respiratory diseases. However, the safety and tolerance for lung disorders are controversy.

Methods

We undertook a systematic review and meta-analyses of all 23 clinical studies of cell therapy. The outcomes were odds ratio (OR), risk difference (RD), Peto OR, relative risk, and mean difference of serious adverse events.

Results

342 systemic infusions and 57 bronchial instillations (204 recipients) of cells were analyzed for acute respiratory distress syndrome (ARDS), bronchopulmonary dysplasia, pulmonary arterial hypertension, silicosis, sarcoidosis, extensively drug-resistant tuberculosis, chronic obstructive pulmonary diseases (COPD), and idiopathic pulmonary fibrosis. The frequency of death in adults from any causes was 71 and 177 per 1,000 for cell therapy and controls, respectively, with an OR of 0.31 (95% CI: 0.03, 3.76) and RD of -0.22 (95% CI: -0.53, 0.09). No significant difference was found for ARDS and COPD. The frequency of deaths and non-fatal serious adverse events of 17 open studies were similar to those of randomized controlled trials. Moreover, serious adverse events of allogenic cells were greater than autologous preparations, as shown by frequency, OR and RD.

Conclusions

We conclude that either infusion or instillation of mesenchymal stem stromal or progenitor cells are well tolerated without serious adverse events causally related to cell treatment. Cell therapy has not been associated with significant changes in spirometry, immune function, cardiovascular activity, and the quality of life.

Thioredoxin-1 Protects Bone Marrow-Derived Mesenchymal Stromal Cells from Hyperoxia-Induced Injury In Vitro

Background

The poor survival rate of mesenchymal stromal cells (MSC) transplanted into recipient lungs greatly limits their therapeutic efficacy for diseases like bronchopulmonary dysplasia (BPD). The aim of this study is to evaluate the effect of thioredoxin-1 (Trx-1) overexpression on improving the potential for bone marrow-derived mesenchymal stromal cells (BMSCs) to confer resistance against hyperoxia-induced cell injury.

Methods

80% O₂ was used to imitate the microenvironment surrounding-transplanted cells in the hyperoxia-induced lung injury in vitro. BMSC proliferation and apoptotic rates and the levels of reactive oxygen species (ROS) were measured. The effects of Trx-1 overexpression on the level of antioxidants and growth factors were investigated. We also investigated the activation of apoptosis-regulating kinase-1 (ASK1) and p38 mitogen-activated protein kinases (MAPK).

Result

Trx-1 overexpression significantly reduced hyperoxia-induced BMSC apoptosis and increased cell proliferation. We demonstrated that Trx-1 overexpression upregulated the levels of superoxide dismutase and glutathione peroxidase as well as downregulated the production of ROS. Furthermore, we illustrated that Trx-1 protected BMSCs against hyperoxic injury via decreasing the ASK1/P38 MAPK activation rate.

Conclusion

These results demonstrate that Trx-1 overexpression improved the ability of BMSCs to counteract hyperoxia-induced injury, thus increasing their potential to treat hyperoxia-induced lung diseases such as BPD.

Strategies to enhance paracrine potency of transplanted mesenchymal stem cells in intractable neonatal disorders

Mesenchymal stem cell (MSC) transplantation represents the next breakthrough in the treatment of currently intractable and devastating neonatal disorders with complex multifactorial etiologies, including bronchopulmonary dysplasia, hypoxic ischemic encephalopathy, and intraventricular hemorrhage. Absent engraftment and direct differentiation of transplanted MSCs, and the "hit-and-run" therapeutic effects of these MSCs suggest that their pleiotropic protection might be attributable to paracrine activity via the secretion of various biologic factors rather than to regenerative activity. The transplanted MSCs, therefore, exert their therapeutic effects not by acting as "stem cells," but rather by acting as "paracrine factors factory." The MSCs sense the microenvironment of the injury site and secrete various paracrine factors that serve several reparative functions, including antiapoptotic, anti-inflammatory, antioxidative, antifibrotic, and/or antibacterial effects in response to environmental cues to enhance regeneration of the damaged tissue. Therefore, the therapeutic efficacy of MSCs might be dependent on their paracrine potency. In this review, we focus on recent investigations that elucidate the specifically regulated paracrine mechanisms of MSCs by injury type and discuss potential strategies to enhance paracrine potency, and thus therapeutic efficacy, of transplanted MSCs, including determining the appropriate source and preconditioning strategy for MSCs and the route and timing of their administration.

Recent advances in our understanding of the mechanisms of late lung development and bronchopulmonary dysplasia

The objective of lung development is to generate an organ of gas exchange that provides both a thin gas diffusion barrier and a large gas diffusion surface area, which concomitantly generates a steep gas diffusion concentration gradient. As such, the lung is perfectly structured to undertake the function of gas exchange: a large number of small alveoli provide extensive surface area within the limited volume of the lung, and a delicate alveolo-capillary barrier brings circulating blood into close proximity to the inspired air. Efficient movement of inspired air and circulating blood through the conducting airways and conducting vessels, respectively, generates steep oxygen and carbon dioxide concentration gradients across the alveolo-capillary barrier, providing ideal conditions for effective diffusion of both gases during breathing. The development of the gas exchange apparatus of the lung occurs during the second phase of lung development-namely, late lung development-which includes the canalicular, saccular, and alveolar stages of lung development. It is during these stages of lung development that preterm-born infants are delivered, when the lung is not yet competent for effective gas exchange. These infants may develop bronchopulmonary dysplasia (BPD), a syndrome complicated by disturbances to the development of the alveoli and the pulmonary vasculature. It is the objective of this review to update the reader about recent developments that further our understanding of the mechanisms of lung alveolarization and vascularization and the pathogenesis of BPD and other neonatal lung diseases that feature lung hypoplasia.

Two-Year Follow-Up Outcomes of Premature Infants Enrolled in the Phase I Trial of Mesenchymal Stem Cells Transplantation for Bronchopulmonary Dysplasia

OBJECTIVE

To determine the long-term safety and outcomes of mesenchymal stem cells (MSCs) for bronchopulmonary dysplasia in premature infants enrolled in a previous phase I clinical trial up to 2 years of corrected age (CA).

STUDY DESIGN

We assessed serious adverse events, somatic growth, and respiratory and neurodevelopmental outcomes at visit 1 (4-6 months of CA), visit 2 (8-12 months of CA), and visit 3 (18-24 months of CA) in a prospective longitudinal follow-up study up to 2 years' CA of infants who received MSCs (MSC group). We compared these data with those from a historical case-matched comparison group.

RESULTS

One of 9 infants in the MSC group died of Enterobacter cloacae sepsis at 6 months of CA, the remaining 8 infants survived without any transplantation-related adverse outcomes, including tumorigenicity. No infant in the MSC group was discharged with home supplemental oxygen compared with 22% in the comparison group. The average rehospitalization rate in the MSC group was 1.4/patient because of respiratory infections during 2 years of follow-up. The mean body weight of the MSC group at visit 3 was significantly higher compared with that of the comparison group. No infant in the MSC group was diagnosed with cerebral palsy, blindness, or developmental delay; in the comparison group, 1 infant was diagnosed with cerebral palsy and 1 with developmental delay.

CONCLUSIONS

Intratracheal transplantation of MSCs in preterm infants appears to be safe, with no adverse respiratory, growth, and neurodevelopmental effects at 2 years' CA.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01632475.

Stem Cell Therapy for Neonatal Disorders: Prospects and Challenges

Despite recent advances in neonatal medicine, neonatal disorders, such as bronchopulmonary dysplasia and intraventricular hemorrhage in preterm neonates and hypoxic ischemic encephalopathy in term neonates, remain major causes of mortality and morbidities. Promising preclinical research results suggest that stem cell therapies represent the next breakthrough in the treatment of currently intractable and devastating neonatal disorders with complex multifactorial etiologies. This review focuses primarily on the potential role of stem cell therapy in the above mentioned neonatal disorders, highlighting the results of human clinical trials and the challenges that remain to be addressed for their safe and successful translation into clinical care of newborn infants.

Stem cell-based therapies for the newborn lung and brain: Possibilities and challenges

There have been substantial advances in neonatal medical care over the past 2 decades that have resulted in the increased survival of very low birth weight infants, survival that in some centers extends to 22 weeks gestational age. Despite these advances, there continues to be significant morbidity associated with extreme preterm birth that includes both short-term and long-term pulmonary and neurologic consequences. No single therapy has proven to be effective in preventing or treating either developmental lung and brain injuries in preterm infants or the hypoxic-ischemic injury that can be inflicted on the full-term brain as a result of in utero or perinatal complications. Stem cell-based therapies are emerging as a potential paradigm-shifting approach for such complex diseases with multifactorial etiologies, but a great deal of work is still required to understand the role of stem/progenitor cells in normal development and in the repair of injured tissue. This review will summarize the biology of the various stem/progenitor cells, their effects on tissue repair in experimental models of lung and brain injury, the recent advances in our understanding of their mechanism of action, and the challenges that remain to be addressed before their eventual application to clinical care.

Recent advances in the mechanisms of lung alveolarization and the pathogenesis of bronchopulmonary dysplasia

Alveolarization is the process by which the alveoli, the principal gas exchange units of the lung, are formed. Along with the maturation of the pulmonary vasculature, alveolarization is the objective of late lung development. The terminal airspaces that were formed during early lung development are divided by the process of secondary septation, progressively generating an increasing number of alveoli that are of smaller size, which substantially increases the surface area over which gas exchange can take place. Disturbances to alveolarization occur in bronchopulmonary dysplasia (BPD), which can be complicated by perturbations to the pulmonary vasculature that are associated with the development of pulmonary hypertension. Disturbances to lung development may also occur in persistent pulmonary hypertension of the newborn in term newborn infants, as well as in patients with congenital diaphragmatic hernia. These disturbances can lead to the formation of lungs with fewer and larger alveoli and a dysmorphic pulmonary vasculature. Consequently, affected lungs exhibit a reduced capacity for gas exchange, with important implications for morbidity and mortality in the immediate postnatal period and respiratory health consequences that may persist into adulthood. It is the objective of this Perspectives article to update the reader about recent developments in our understanding of the molecular mechanisms of alveolarization and the pathogenesis of BPD.