Cell-based therapies for the preterm infant

Cytotherapy, 2014; 0: 1e15

Cell-based therapies for the preterm infant DANDAN ZHU1, EUAN M. WALLACE1,2 & REBECCA LIM1,2 1

The Ritchie Centre, Monash Institute of Medical Research, and the 2Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia

Abstract The severely preterm infant receives a multitude of life-saving interventions, many of which carry risks of serious side effects. Cell therapy is an important and promising arm of regenerative medicine that may address a number of these problems. Most forms of cellular therapy use stem/progenitor cells or stem-like cells, which have the capacity to migrate, engraft and exert anti-inflammatory effects. Although some of these cell-based therapies have made their way to clinical trials in adults, little headway has been made in the neonatal patient group. This review discusses the efficacy of cell therapy in preclinical studies to date and their potential applications to diseases that afflict many prematurely born infants. Specifically, we identify the major hurdles that must be overcome before cell therapies can be safely used in the neonatal intensive care unit. Key Words: bronchopulmonary dysplasia, cell therapy, human amnion epithelial cells, mesenchymal stromal cells, prematurity

Introduction Preterm birth is defined as birth before 37 weeks of gestation (1). The incidence of preterm birth is associated with prenatal mortality, neonatal morbidity and childhood disability. Preterm birth remains the leading cause of neonatal deaths in children under 5 years of age, second only to pneumonia (2). Although there has been a gradual decline in the perinatal mortality as the result of improvements in overall clinical management, the mortality rate of preterm infants born at 32e36 weeks has remained 3- to 5-fold higher compared with that of term infants (3,4). The mortality rate in infants born at 22e23 weeks is more than 3-fold higher than those born at 28 weeks (5). There are a multitude of complications associated with being born preterm, many of which are indirect consequences of life-saving interventions, including respiratory distress syndrome and bronchopulmonary dysplasia (BPD). Cell therapy may be a suitable adjuvant therapy for indications in which inflammation and tissue damage prevail. In this review, we will identify the most common diseases that affect premature infants who are amenable to cell therapy. We will describe current clinical management as well as preclinical evidence of efficacy with the use of cell therapies. Respiratory diseases Premature infants born at 33e36 weeks’ gestation are more than 4 times as likely to have neonatal respiratory

morbidity compared with their term counterparts (6). These respiratory complications include respiratory distress syndrome, BPD and secondary pulmonary hypertension. Respiratory distress syndrome is the single most important cause of illness and death in preterm infants caused by developmental insufficiency of surfactant production and structural immaturity in the lungs. BPD is commonly associated with mechanical ventilation and oxygen therapy of severely preterm infants, which results in abnormal lung development, decreased lung compliance, oxidative stress and inflammation (7). Collectively, these respiratory disorders have serious adverse long-term health consequences on the severely preterm infant including abnormal lung and airway development and increased susceptibility to respiratory disease (8). Ventilation is considered a major pillar of critical care medicine in premature infants, especially for those with respiratory diseases. Although ventilation strategies have become less injurious over the years (9,10), the deleterious effects on underdeveloped organs can be profound. A high fraction of inspired oxygen (FiO2) is associated with increased incidence of BPD (11) and retinopathy of prematurity (12), whereas low FiO2 induces hypoxic ischemic encephalopathy and necrotizing enterocolitis (13). Consequently, many clinical centers now emphasize low lung volume and avoiding endotracheal ventilation (14,15). Current clinical management for respiratory diseases in preterm infants includes suppressing lung

Correspondence: Rebecca Lim, MD, The Ritchie Centre, Monash Institute of Medical Research, 27e31 Wright Street, Clayton, Victoria 3168, Australia. E-mail: [email protected] (Received 27 November 2013; accepted 26 June 2014) http://dx.doi.org/10.1016/j.jcyt.2014.06.004 ISSN 1465-3249 Copyright Ó 2014, International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.

2

D. Zhu et al.

inflammation and infection, and improving pulmonary function. For example, surfactant is widely used in preterm infants to reduce the risk of developing respiratory distress syndrome (16). Corticosteroids suppress pulmonary inflammation and improve pulmonary function. Systemic postnatal corticosteroids are used early (
7 days) to prevent the development of BPD (17) and are used later (>7days) to treat pulmonary diseases (18). Caffeine is recommended for reducing the numbers of apneic attacks in preterm infants (19) and for the prevention of BPD in very low birth weight infants (20). Although there are advances in treatments, some therapies have no advantages or even have significant adverse effects. For example, systemic corticosteroids use, though effective, can cause adverse effects of neurodevelopment (17,18), and inhaled corticosteroid administration neither prevents nor treats BPD (21). Neurological diseases Challenges faced by the premature infant are not limited to respiratory conditions. Common neurological diseases associated with preterm birth include intraventricular hemorrhage, periventricular leukomalacia and sequelae such as cerebral palsy and cognitive impairment. The premature brain is highly susceptible to hypoxia. Most brain insults occur secondary to perinatal hypoxia or asphyxia. An estimated 20e25% of infants with very low birth weight (<1500 g) have intraventricular hemorrhage, which has been attributed to alterations in cerebral blood flow to the immature and fragile germinal matrix microvasculature and secondary periventricular venous infarction (22). Risk factors of intraventricular hemorrhage include severe respiratory distress syndrome and patent ductus arteriosus, which can induce intraventricular hemorrhage through fluctuations in blood flow (23). Another common neurological disorder in premature infants is periventricular leukomalacia, which can either occur in isolation or in conjunction with intraventricular hemorrhage. The pathological hallmark for periventricular leukomalacia is the focal and diffuse periventricular depletion of immature premyelinating oligodendroglia, which are highly vulnerable to ischemic and inflammatory injuries (24). The pathogenesis of neurological diseases in preterm infants is largely caused by immaturity of the brain structure and cells as well as the unstable cerebral blood flow. Management is currently confined to screening for sequelae such as posthemorrhagic hydrocephalus. Because of the significant adverse effects of short- and long-term sequelae in later life, clinical trials have focused on prevention strategies. For example, phenobarbital, indomethacin and

ibuprofen are used to prevent intraventricular hemorrhage (25). Phenobarbital is used for stabilization of blood pressure and free radical production. Indomethacin is used to promote microvascular maturation and blunt fluctuations in cerebral blood flow by closing patent ductus. Ibuprofen is used to improve autoregulation of cerebral blood flow. However, meta-analysis showed no difference in the incidence and severity of intraventricular hemorrhage after intervention (25,26). Gastroenterological diseases Necrotizing enterocolitis (NEC) is another inflammatory disease that primarily affects premature infants. It is the leading cause of gastrointestinal mortality and morbidity in preterm infants. The incidence of necrotizing enterocolitis in preterm birth is reportedly 9 times greater than that of term birth (27). The etiology of NEC is different in term compared with preterm infants. In term infants, hypoxia-ischemia is a common precursor for NEC (13) and usually is associated with other diseases such as congenital heart disease (28). In contrast, the etiology and pathogenesis of NEC in preterm infants is not completely understood. It is, however, acknowledged that the disease is multifactorial. Inflammation was recently reported to be the dominant underlying cause of NEC (29); other risk factors include intestinal immaturity, abnormal intestinal microbial colonization and hypoxic ischemic injury (30). Immature motility, digestion, absorption, barrier function and immune defence contribute to the high incidence of NEC in preterm infants (31). Premature enterocytes have an excessive and inappropriate inflammatory response to postnatal bacterial colonization in which inflammation further increases intestinal permeability. A pathological microbial colonization increases the risk of NEC in preterm infants by inducing an inflammatory response (32). Vascular regulators such as nitric oxide and endothelin, consequent to hypoxic ischemic injury, can further compound NEC by altering the microvascular environment (33). Current clinical treatments include abdominal decompression, bowel rest, broad-spectrum intravenous antibiotics and intravenous hyperalimentation; surgical interventions are required for infants with severe NEC (31). Control of inflammation in NEC is critical, and, although broad-spectrum intravenous antibiotics can suppress the infection, secondary infections can occur as the result of changes in the microbial colonization. Surgical interventions, which include laparotomy and primary peritoneal drainage, are applied to the most advanced cases, but there is currently no consensus as to the primary surgical

Cell-based therapies for the preterm infant intervention (13). Probiotics, prebiotics and synbiotics are suggested to use for the prevention of NEC, but larger independent trials are needed to assess efficacy (34).

Table I. Summary of preclinical studies of stem/progenitor cells for diseases of prematurity. Cell type Mesenchymal stem/stromal cells

Ophthalmological diseases Blindness is another common outcome for premature infants. Retinopathy of prematurity can occur as a consequence of supplemental oxygen administered during ventilation. The hyperoxic condition for preterm infants induces vasoconstriction and peripheral ischemia. Furthermore, longer periods of hyperoxia lead to retinal neovascularization as the result of vascular endothelial growth factor (VEGF) overproduction; this results in disrupted postnatal retinal vasculogenesis (12). The reported incidence of retinopathy of prematurity has been as high as 45.6% in infants with birth weight <1000 g or 40.3% in those at <30 gestational weeks (35). Cryotherapy and transpupillary laser treatments, which can prevent retinopathy of prematurity (ROP) progression, are widely used in the past three decades (12). However, these approaches come with many complications, including burns to the cornea, iris and lens as well as preretinal, retinal and vitreous hemorrhage and hyphema (36). Current drug therapies for ROP target VEGF signaling. The safest and most effective to date is bevacizumab, which is used as monotherapy for ROP (37). However, potential side effects have not yet been verified. While many pharmacological therapies can provide symptomatic relief, functional improvement and reduction in short-term mortality, survivors of prematurity can also be predisposed to adverse health problems later in life (38). For example, they are at greater risk for the development of hypertension (39), asthma (40), cerebral palsy (41), psychiatric morbidity and impaired cognitive function in adulthood (42,43). Our improved understanding of the repercussions of premature birth is reflected in the change in clinical management in which the focus has shifted from damage control to restoration of normal function.

3

Endothelial progenitor cells Neural stem/progenitor cells Embryonic stem cells

Preclinical studies Bronchopulmonary dysplasia associated with pulmonary hypertension (170), ischemic brain injury (163) and necrotizing enterocolitis (167) Retinopathy (171), bronchopulmonary dysplasia and associated pulmonary hypertension (65) Cerebral palsy (172), stroke (173) and intracerebral hemorrhage (174) Cerebral palsy (175) and central nervous system injury (175)

embryonic stem cells (ESCs), neural stem cells and induced pluripotent stem cells (iPSCs). Although there are some preclinical studies focusing on the application of stem/progenitor cells to diseases affecting premature babies (Table I), only four clinical trials can be found in the National Institute of Health registry (Table II) compared with the vast number of clinical trials using stem/progenitor cells for treatment of diseases affecting adults and children (Table III). ESCs have the greatest potential to form many cell types but have seen a decline in popularity for clinical research because of ethical concerns as well as potential tumorigenicity (44). In light of this, iPSCs have been touted as a potential replacement for ESCs. iPSCs are pluripotent stem cells induced from terminally differentiated somatic cells by means of epigenetic remodeling (45). Patient-specific iPSCs have been used for disease modeling (46,47), and some preclinical studies on iPSC-derived cell therapy have been reported. These include treatment for murine sickle cell anaemia with autologous iPSCderived hematopoietic progenitor cells and rescue of murine cardiac disorder through the use of human iPSC-derived cardiovascular progenitor cells (48,49). However, there have been no preclinical studies addressing the use of iPSCs for diseases of prematurity to date. MSCs and EPCs can be isolated from tissues such as bone marrow, adipose tissue and peripheral blood, but the most attractive sources are gestational

Cell therapies Cell therapy is being explored as a therapeutic modality for a variety of diseases. The therapeutic and regenerative potential of stem/progenitor cells is associated with their capacity to migrate and engraft into functional tissues as well as their potent anti-inflammatory properties. A variety of stem/progenitor cells have been proposed for the treatment of diseases affecting premature babies. These include mesenchymal stem/stromal cells (MSCs), endothelial progenitor cells (EPCs),

Table II. Clinical trials for diseases of prematurity.

Cell type Mesenchymal stem/stromal cells

Bone marrowederived stem cells

Clinical indication Bronchopulmonary dysplasia Acute respiratory distress syndrome Acute respiratory distress syndrome

ClinicalTrials.gov reference No. NCT01385644 NCT0182895 NCT01902082 NCT01775774

4

D. Zhu et al.

Table III. Clinical trials that used stem/progenitor cells in adults and children. Cell type Mesenchymal stem/stromal cells

Endothelial progenitor cells

Bone marrowederived stem cells

Neural stem/progenitor cells

Embryonic stem cells

Clinical indication Acute myocardial infarction Myocardial ischemia Critical limb ischemia Crohn’s disease Graft-versus-host disease Multiple sclerosis Degenerative arthritis Osteoarthritis Liver cirrhosis Ischemic stroke Diabetes mellitus Amyotrophic lateral sclerosis Spinal cord injury Ischemic stroke Critical limb ischemia Liver cirrhosis Pulmonary hypertension Coronary artery disease Stroke Critical limb ischemia Spinal cord injuries Chronic ischemic heart failure Amyotrophic lateral sclerosis Liver cirrhosis Diabetes mellitus Spinal cord injury Amyotrophic lateral sclerosis Stroke Age-related macular degeneration Stargardt’s macular dystrophy Age-related macular degeneration

tissues. They are a rich source of stem cells and stemlike cells and are not associated with the legal, ethical, moral or religious concerns because they are usually discarded after delivery. Hematopoietic stem cells (HSCs), EPCs, MSCs and human amnion epithelial cells (hAECs) can be isolated from sources including the placenta, umbilical cord blood, Wharton’s jelly, amniotic fluid, placenta and fetal membranes (Figure 1). Umbilical cord blood Human umbilical cord blood (UCB) contains HSCs, EPCs and MSCs. After the first successful cord bloodederived HSC transplantation in 1988 (50), the first public umbilical cord blood bank was established in 1993 at The New York Blood Center. In the past 20 years, many public and private cord blood banks have been established globally. Early protocols for the collection of UCB involved the freezing of whole blood without fractionation because early iterations of physical separation procedures resulted in significant loss of the progenitor cell fraction (51). New separation procedures detail the banking of either whole cord blood or different fractions of stem cells, followed by

ClinicalTrial.gov reference No. NCT01392105 NCT01076920 NCT01456819 NCT00294112 NCT01765634 NCT01895439 NCT00891501 NCT01499056 NCT00420134 NCT01297413 NCT01157403 NCT01771640 NCT01694927 NCT01468064 NCT01595776 NCT01333228 NCT00641836 NCT00494247 NCT01501773 NCT01472289 NCT01730183 NCT00747708 NCT01758510 NCT01724697 NCT01694173 NCT01772810 NCT01640067 NCT01151124 NCT01632527 NCT01469832 NCT01691261

isolation, culture and flow cytometric purification of nucleated cells (52,53). Cord blood stem cell transplantation is often limited by the volume collected because the minimal numbers of cord blood stem cells required for clinical use has been estimated to be approximately 1e2  107 nucleated cells/kg (54). Because the average yield of nucleated cells in one cord blood unit is 3e4  108, it is unlikely that cord blood stem cells can be applied to adults. Their use is thus generally limited to infants and children. There are two ways to overcome this limitation. One is to use pooled units of cord blood. Although it is possible that cord bloodederived stem cells pooled from different donors could be used for bone marrow reconstruction (55), finding human leukocyte antigen (HLA) matches in two or more cord blood donors will be challenging and may add complexity to the process. The other way to overcome this limitation, which is popular for preclinical and clinical trials, is the ex vivo expansion for cord bloode derived stem cells. HSCs are the main population of stem cells from the UCB. CD34þ cells are purified from total mononuclear cells before selection for non-adherent

Cell-based therapies for the preterm infant

Figure 1. Origin and application of gestational tissueederived stem cells and stem-like cells to diseases of prematurity. Gestational tissues, which include the placenta, fetal membrane, umbilical cord blood, Wharton’s jelly and amniotic fluid, are attractive sources for stem cells and stem-like cells. MSCs, EPCs and hAECs isolated from these sources were applied to different diseases of prematurity.

cells in culture (56). Although the number of HSCs from a single UCB unit is sufficient for neonatal transplantation, culture systems have been developed for ex vivo expansion to meet adult needs (57). However, the clinical use of UCB-HSCs has largely been limited to applications toward hematopoietic disorders such as leukemia, Fanconi anemia and autoimmune disorders rather than diseases of prematurity. EPCs exist in bone marrow, peripheral blood and UCB, in which they account for 2% of CD34þ cells in UCB. UCB-derived EPCs have greater proliferative potential and higher cell cycle rate compared with EPCs from other sources (58). Although UCB-derived EPCs are generally described as adherent cells positive for stem cell markers (CD34, CD133 and CD90) and endothelial cell markers (CD31, CD144 and CD309), there is no consensus on specific markers for UCBderived EPCs (59,60). The low percentage of EPCs in UCB and lack of specific markers make isolation and characterization challenging. Endothelial colony-forming cells (ECFCs), a subtype of EPCs derived from CD34þ/CD45 nonhematopoietic EPCs, can be identified by means of an assay generated from the endothelial outgrowth methodology. Briefly, CD34þ/CD45 cells from UCB are cultured on pre-coated dishes. ECFC colonies will form after 1e3 weeks of culture (61), with an average number of 45 ECFCs from one UCB unit (62). Further 2- to 3-week culture of ECFCs gives a general yield of 108 cells (63). ECFCs actively proliferate, generate typical endothelial cell colonies and form perfused vessels in vivo (64). In a preclinical study that used a mouse model of BPD, term UCBderived ECFC-conditioned medium reduced right ventricular hypertrophy (65). Additionally, intravenous injection of ECFCs effectively promoted

5

neovascularization and improved neurological functions in mice with brain injury (66). MSCs can also be isolated from UCB. Although the bone marrow is the most common source of MSCs, there are some disadvantages to the use of bone marrowederived MSCs. These include the highly invasive procedure, limited cell yield and proliferative potential particularly in aged donors and virally infected individuals (67,68). More recently, the placenta (69), umbilical cord blood (70), Wharton’s jelly (71) and endometrium (72) have been introduced as alternative sources. Core gene expression and physical properties are largely conserved across the different sources of MSCs. These include morphology, growth characteristics, cell surface markers, chemokine receptor display, differentiation potential and immunosuppressive capabilities (73e75). To overcome the low abundance of MSCs in UCB, the isolated MSCs can be expanded with high efficiency. First, CD34/CD45 cells are selected from mononuclear cells and cultured for further selection of plastic adherent cells. These are then serial passaged in Dulbecco’s modified Eagle’s medium (DMEM) and MCDB media supplemented by 15% fetal bovine serum (76). The UCB-MSCs are then further purified by flow cytometric sorting for CD105þ, CD90þ, CD49eþ, CD73þ and CD44þ cells and CD45, CD34, CD19, CD31, CD56 and CD14 cells (76,77). The expected UCB-MSC yield is w2  106 after 10 days in primary culture, and further 10-fold expansion can be achieved in 4 weeks (77). Although efficient expansion of UCBderived MSCs is clearly possible, low isolation success rates (10e40%) have been reported (77,78). A Korean-based biotech company, Medipost, Seoul, began clinical trials with the use of cord bloode derived MSCs (Pneumostem) for the treatment of established BPD and showed that intratracheal transplantation of allogeneic UCB-derived MSCs in preterm infants is safe and that the pro-inflammatory cytokines interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-a and transforming growth factor (TGF)-b1 were reduced in tracheal aspirates 7 days after transplantation (79). Amniotic fluid and Wharton’s jelly MSCs are the most well-described stem cells from amniotic fluid and Wharton’s jelly. The process of isolating MSCs from the amniotic fluid is relatively simple. It involves the selection of plastic adherent cells and serial passaging in a-minimum essential medium or high glucose DMEM media supplemented by 20% fetal bovine serum and fibroblast growth factor. Further purification is attained by

6

D. Zhu et al.

means of phenotypic flow cytometric sorting for CD166þ, CD105þ, CD90þ, CD49eþ and CD73þ and CD45, CD34, CD19, CD8, CD31, CD56 and CD14 cell populations (80,81). Similarly, MSC isolation from Wharton’s jelly begins with the mechanical dissociation of tissue explants or enzymatic dissociation for cell pellets, followed by serial passaging in DMEM media supplemented with 10e20% fetal bovine serum (82,83). The average yield of MSCs from second-trimester amniotic fluid is reportedly 2  108 after 5 weeks in culture, with w50% isolation success rate (84). In contrast, the average yield of Wharton’s jellyederived MSCs is w2e5  105 cells/g after 2 weeks in culture (85). Placenta and fetal membranes Stem cells and stem-like cells that can be isolated from placenta and fetal membranes for regenerative medicine include hAECs and MSCs (45). Placental MSCs (pMSCs) refer collectively to MSCs isolated from the fetal membranes (amnion and chorion) as well as placental tissue, which is primarily of maternal origin (decidua basalis and decidua parietalis). pMSCs isolated from fetal membranes can be further classified as human amnion mesenchymal stem/stromal cells (hAMSCs) and human chorion MSCs, respectively. The isolation process begins with the removal of epithelial cells from the amnion and the trophoblastic layer from the chorion with subsequent collagenase and dispase digestion (86,87). Similarly, pMSCs are isolated with the use of collagenase and DNase digestion (73). pMSCs are then selected through the use of a combination of plastic adherence under tissue culture conditions and phenotypic surface markers. The average yield of hAMSCs is w4  106 from a term amnion, and the 4-fold serial expansion can be achieved in an average of 4 weeks (88,89). The process of isolating hAECs includes the physical separation of the amniotic membrane from the chorion, followed by trypsin digestion to release the hAECs from the membrane. The cells are then collected and cryopreserved in liquid nitrogen (90,91). The isolation procedure is relatively short, with an average yield of 120  40  106 within 4 hours from a single amniotic membrane (90). From all the above stem and stem-like cells that can be isolated from gestational tissues, ECFCs from UCB and MSCs from UCB, amniotic fluid and Wharton’s jelly require weeks of ex vivo expansion before clinical use. In contrast, the numbers of freshly isolated hAECs and pMSCs are sufficient for clinical use in neonates without the need for ex vivo expansion. This is advantageous, given the unstable clinical condition of severely ill premature infants, in

whom the rapidity of clinical intervention may be life-saving. This being said, autologous transplantation is not always beneficial or feasible. For instance, the sterility of cells isolated from the placental tissues or fetal membranes in babies affected by chorioamnionitis probably will be compromised. Additionally, babies who are affected by preeclampsia are likely to have a smaller placenta, having been subjected to chronic oxidative stress and inflammation. These pathological pregnancies are likely to affect the quality of cells obtained. In support of this, there is some in vivo evidence to suggest that hAECs obtained from preterm placentas produced lower levels of the immunomodulatory protein HLA-G and were able to prevent lung injury compared with the term hAECs (92). Regenerative and reparative properties of hAECs and pMSCs hAECs and MSCs do not express HLA-DR (class II) (91,93,94), which suggests that they may be able to evade immune recognition and are less likely to be rejected on transplantation. Flow cytometric analyses indicate that hAECs and MSCs do not express hematopoietic markers such as CD34 and CD45 and stain positive for the following markers: CD44, CD49e, CD73, CD90 (Thy-1), CD105, CD166 and STRO-1 (69,94e96). Both hAECs and MSCs express octamer-binding protein 4 (86,97). Interestingly, hAECs do not express telomerase but retain long telomeres, normal karyotype and cell cycle distribution even after five passages (96). This supports the current consensus that hAECs are unlikely to form tumors after transplantation, compared with embryonic stem cells, which are susceptible to karyotypic abnormalities after serial passaging (98). hAECs can differentiate down the adipogenic, chondrogenic, osteogenic, cardiomyocytic, hepatic, pancreatic and neural lineages in vitro (88,95,99). The hepatic, pancreatic and neural differentiation of hAECs also has been well described in vivo. For instance, hAECs transplanted into the lateral ventricle of a rat differentiated into tyrosine hydroxylaseepositive cells (100). Furthermore, the hAECs synthesized and released neurotransmitters, including acetylcholine, catecholamines and dopamine (101). In a mouse model of hepatic fibrosis, human albumin was detected in the serum and human DNA was detected in the liver (102). The transplantation of hAECs into streptozotocin-induced diabetic mice reversed hyperglycemia and maintained euglycemia (103), and, in a sheep model of ventilation-induced preterm lung injury, hAECs differentiated into type I and type II alveolar cells (104).

Cell-based therapies for the preterm infant Similarly, pMSCs have multilineage differentiation capacity in vitro, which includes adipogenic, chondrogenic, osteogenic, neurogenic, skeletal myogenic, pancreatic and cardiomyogenic differentiation (69,105e109). Cardiac, muscular and chondrogenic differentiation of pMSCs have also been described in vivo. Specifically, hAMSCs survived in the myocardium for more than 2 months and differentiated into cardiomyocyte-like cells in a rat model of myocardial infarction (109). In nude rats with osteochondral defects, transplanted pMSCs produce substantial cartilage matrix and differentiate into collagen type IIeproducible chondrocytes (110,111). Anti-inflammatory properties of hAECs and pMSCs hAECs exert anti-inflammatory effects both in in vitro and in vivo. The anti-inflammatory effect of hAECs appears to be primarily achieved by reducing leukocyte trafficking and modulating the macrophage phenotype. Supernatant from hAECs significantly inhibited chemotactic activity of neutrophils and macrophages and reduced proliferation of T and B cells after mitogenic stimulation (93). Also, hAECconditioned media promoted polarization of bone marrowederived macrophages from a pro-inflammatory M1phenotype to a pro-reparative M2 phenotype (112). hAECs decreased inflammation in both immune-deficient and immune-competent animals without immune rejection. This ability to evade immune surveillance has been associated with low levels of HLA (113). There is a growing body of evidence that hAECs have profound anti-inflammatory effects. In a mouse model of multiple sclerosis, in which hAECs were administered systemically, levels of interferon (IFN)-g, TNF-a and granulocyte-macrophage colony-stimulating factor were significantly reduced. Concurrently, IL-5 and IL-10 were increased, which strongly suggests a shift from Th1 to Th2 (114). The expression of IL-1b in the eyes of mice with corneal inflammation was dramatically reduced after being treated with hAEC-conditioned media (115). Administration of hAECs to mice with lung injury significantly decreased gene expression of the proinflammatory cytokines TNF-a, TGF-b, IFN-g and IL-6 (116). hAECs also attenuated lung inflammation in fetal sheep by reducing TNF-a, IL-1b and IL6 induced by intra-amniotic lipopolysaccharide (LPS) injection (117). The absence of this effect in Sftpc (/) mice, which bear dysfunctional macrophages, suggests that macrophages are important to hAEC action (118). Regardless of their tissue origin, MSCs share a number of similar properties (74,119). MSCs are

7

also able to exert anti-inflammatory effects by modulating subsets of T-helper cells, B cells and dendritic cells. MSCs shift the Th1/Th2 balance by reducing Th1 proinflammatory cytokines IL-1b, IFN-g and TNF-a and increasing Th2 cytokines IL10 and IL-4 (120,121). MSCs have also inhibit Tcell proliferation and induce CD4þCD25þ T-cell expansion by releasing soluble factors including prostaglandin E2, IL-10, TGF-b1, hepatocyte growth factor (HGF) and indoleamine 2,3-dioxygenase (122). Additionally, MSCs have been shown to inhibit the proliferation and function of dendritic cells by increasing IL-10 secretion (123,124). MSCs are further able to inhibit B-cell proliferation by downregulating CXC chemokine and the receptors (125). These immunomodulatory properties of MSCs are currently being exploited in clinical trials (NCT00361049, NCT 00504803). Anti-fibrotic properties of hAECs and pMSCs hAECs exert anti-fibrotic effects both in vitro and in vivo, specifically by modulating the function and activation state of myofibroblasts (126). hAEC administration has been shown to prevent (116) and reverse (127) bleomycin-induced lung fibrosis in mice, concomitant with reduced macrophage numbers and decreased levels of TNF-a, IFN-g and IL-6 (116,128). Similarly, in the carbon tetrachloride mouse model of hepatic fibrosis, hAECs reduced TGF-b1, shifted macrophage phenotype from M1 to M2 and decreased the activation of collagen-producing hepatic stellate cells (129). These studies support the use of hAECs for targeting fibrotic diseases. Similarly, MSCs have been shown to exert antifibrotic actions associated with the downregulation of TGF-b signaling and reduction in Smad2 phosphorylation in bleomycin-induced lung injury (130). MSC-conditioned media inhibited TNF-a production by activated macrophages in vitro, and MSC transplantation blocked TNF-a and IL-1 in bleomycin-induced mouse lung injury (131). Moreover, MSCs attenuated cardiac and liver fibrosis in mice by reducing collagen deposition and increasing the activity of matrix metalloproteinase 2 and 9 (MMP-2 and MMP-9) (132,133) and increased HGF expression (134). Angiogenic effects of pMSCs and hAECs There are controversial reports on the angiogenic effects of pMSCs and hAECs. hAMSCs secrete angiogenic factors including the tissue inhibitor of metalloproteinases (TIMP)-1, TIMP-2, epidermal growth factor (EGF), angiogenin and VEGF.

8

D. Zhu et al.

Similarly, hAECs secrete VEGF, platelet-derived growth factor B, TIMP-1, TIMP-2, EGF and angiogenin (135,136). In the dorsal skinfold chamber model, the number and length of vessel sprouts increased when the mesenchymal side of the amnion was in contact with the animal tissue. In comparison, when the epithelial side of the amnion was in contact with the animal tissue, the number of vessel sprouts remained unchanged but the vessels were shorter compared with the control group (137). It is clear, however, that the microenvironment can affect stem cell function. For example, MSCs exert pro-angiogenic effects during wound healing by means of VEGF and HGF and maintaining a balance between TGF-b1 and TGF-b3 (138). However, MSCs also reduced neovascularization in chemically injured rat cornea by upregulating thrombospondin1 and downregulating MMP-2 (139). Similarly, hAEC-conditioned media suppressed neovascularization in intra-stromal sutures imbedded in mouse cornea by inhibiting IL-1b (140). MSCs and hAECs support healing process indirectly Studies on the therapeutic properties of MSCs and hAECs have investigated the application of the cells themselves as well as their conditioned media, because both contribute to the healing process. There are published reports of MSC engraftment in the kidneys, lungs and intestines (141e143). Similarly, hAEC engraftment in the liver, lung and brain has been reported (144e146). However, there are increasing numbers of reports that MSC engraftment is rare (147,148) and that similar effects can be achieved with the use of MSC-conditioned media (149). The engraftment of hAECs is also rare despite apparent protective effects in vivo (117,150). These observations have led to a series of studies geared to dissecting the components of the conditioned media. The proteome of bone marrowederived MSCeconditioned media analyzed by means of mass spectroscopy includes extracellular proteins, such as matrix components with fibronectin, heparan sulfate proteoglycan and collagen. They also include factors related to immune modulation such as osteopontin and macrophage colony-stimulating factor 1 (151). The mobilization of EPCs by macrophage colonystimulating factor 1 in MSC-conditioned media could be a mechanism in treatment for animals with lung injury (149). Most recently, exosomes in the conditioned media of MSCs have been characterized (152,153). Exosomes are shed by the cells and range from 40e100 nm in diameter and can serve as signaling transporters of micro RNA and messenger RNAs as well as a number of peptides and proteins (154). Exosomes shed by cord bloodederived MSCs

have been shown to inhibit vascular remodeling and hypoxic pulmonary hypertension in mice through suppressing signal transducer and activator of transcription 3 (STAT3) and downregulating the miR-17 superfamily of micro RNA (155). Notably, the exosomal content of hAEC-conditioned media has not been described to date. Preclinical application of hAECs and pMSCs to perinatal diseases Although there is only one registered clinical trial (Australia Clinical Trails) attempting to describe the safety and efficacy of hAEC administration to preterm neonates with BPD (ACTRN12614000174684), the therapeutic effects of hAECs in the context of respiratory diseases (127), central nervous system diseases (156) and metabolic diseases (103,157) have been described in preclinical studies. In the application of hAECs to perinatal disease, this has largely focused on BPD and neurological diseases. BPD is characterized by diffused reduction of alveolar development combined with airway injury, inflammation and fibrosis. Antenatal inflammation and treatment with high-flow oxygen (hyperoxia) are key contributors to the development of BPD. As such, animal models of BPD focus on replicating these aspects of the clinical condition. In a sheep model of BPD in which LPS was introduced intraamniotically to induce antenatal inflammation, hAECs administered into the fetus attenuated the fetal pulmonary inflammation, increased surfactant protein-A and surfactant protein-C and normalized lung function and histology (117). In another sheep model of BPD in which fetal lamb lungs were ventilated in utero, hAEC treatment reduced fibrosis and the deposition of collagen and elastin by reducing TGF-b1 and a-smooth muscle actin, which may be the result of hAEC modulated myofibroblast differentiation (104). A subsequent study showed that hAECs normalized lung tissue density, collagen content and a-smooth muscle actin production in association with reduction of inflammation in established lung fibrosis (118). Administration of hAECs reduced fetal brain injury in an LPS-induced intrauterine inflammation sheep model, in which cell death within and surrounding the white matter lesion sites was decreased by reducing the number of microglia and terminal deoxynucleotidyl transferase dUTP nick end labelingepositive cells after hAEC transplantation (150). hAEC treatment also reduced brain edema and improved motor deficits when transplanted into the lateral ventricle of rats with intracerebral hemorrhage (158). Transplantation of hAECs into the spinal cord in monkeys and rats after experimental spinal cord

Cell-based therapies for the preterm infant injury supported axonal growth, prevented the death of axotomized neurons and improved hind limb motor function (156,159). Furthermore, transplanted hAECs survived for more than 10 weeks in the lateral ventricle and 60 days in the spinal cord (89,160), in which transplanted cells improved brain function, exhibited neuroprotective effects in acute phases and improved long-term recovery in spinal cord injury. These beneficial effects were mediated through released neurotransmitters and novel neurotrophic factors such as epidermal growth factor and fibroblast growth factor-2 (161). These preclinical studies suggest that hAECs could be an effective therapy for perinatal neurological diseases. Retinopathy of prematurity occurs as the result of incomplete vascularization of the retina in premature infants. The normal vascular formation is disrupted after birth, and increased levels of VEGF stimulate pathological neovascularization. Thus, new treatments focus on anti-VEGF and suppression of neovascularization (36). Conditioned media from hAECs significantly suppressed corneal neovascularization in a mouse model of corneal injury by releasing antiinflammatory factor IL-1 receptor antagonist (115).

9

This suggests that hAEC application for retinopathy of prematurity may be plausible; however, this hypothesis has yet to be tested. Although there have been several preclinical studies focusing on perinatal applications of bone marrowederived and cord bloodederived MSCs, there is an obvious dearth in our knowledge on the application of pMSCs. Despite this, there are three registered clinical trials to date, focusing on the application of pMSCs to diseases affecting adults, such as type 2 diabetes (NCT01413035), ankylosing spondylitis (NCT01420432) and idiopathic pulmonary fibrosis (NCT01385644). Applications of bone marrowederived and cord bloodederived MSCs to perinatal diseases Because the bone marrow and umbilical cord blood are the common sources for MSCs, there are a number of preclinical studies describing the application of these to perinatal diseases. In a mouse model of hyperoxia-induced BPD, administration of bone marrowederived MSCs reduced inflammation and protected alveolar architecture (151). A separate

Figure 2. Mechanisms by which MSCs, EPCs and hAECs can rescue common diseases of prematurity. IVH, intraventricular hemorrhage; PVL, periventricular leukomalacia; AT2 cell, alveolar type 2 cell; a-SMA, a-smooth muscle actin;; MT3, methallothin-3; NGF, nerve growth factor; PAEC, pulmonary artery endothelial cell; SDF-1, stromal cellederived factor-1; SP, surfactant protein.

10

D. Zhu et al.

study indicated that intra-tracheal delivery of bone marrowederived MSCs could prevent arrested alveolar growth and attenuate alveolar and lung vascular injury and pulmonary hypertension in hyperoxia-induced neonatal rat lung injury (162). A long-term experiment on hyperoxia-induced BPD in rats showed that persistent improvement in exercise capacity and lung structure was observed 6 months after transplantation of cord bloodederived MSCs (147). In perinatal neurological diseases, transplantation of bone marrowederived MSCs to the right hemisphere in rat pups with ibotenic acideinduced periventricular white matter injury increased myelin levels in the corpus callosum and improved the reaching and retrieval function, which were associated with MSC migration to lesion sites and increased cell proliferation (163). Another study that used a neonatal rat model of hypoxic ischemic encephalopathy showed that there were no differences in the distribution of MSCs between the lesioned and contralateral cerebral hemispheres, but neurological performance of the neonatal rats improved after MSC transplantation (164). Even in models of severe brain injury such as permanent middle cerebral artery occlusion, transplantation of cord bloode derived MSCs decreased infarct volume and improved brain function (165). Administration of MSCs to rats subjected to an experimental model of necrotizing enterocolitis resulted in reduced histopathological damage and enhanced the survival rate, which was achieved by lowering intestinal permeability, decreasing intestinal dilation and perforation (166,167). This suggests that MSCs may be a promising therapy for necrotizing enterocolitis because the current medical management is inadequate and may have severe complications.

Preclinical applications of pMSCs to perinatal diseases Although pMSC application to perinatal diseases has not been tested to date, some studies that used adult animal models suggest that pMSCs may be useful. For example, pMSCs have been shown to prevent lung fibrosis and decreased neutrophil infiltration in adult mice (146), which suggests that pMSCs may rescue perinatal lung disease accompanied by inflammation, such as BPD. Moreover, pMSC (168) and hAMSC (169) transplantation to a rat model of stroke reduced infarct volume and improved neurological reactivity score. These may support the application of pMSCs to perinatal neurological diseases such as hypoxic-ischemic encephalopathy and cerebral palsy (176e178).

Conclusions Cell therapy is an important and promising arm of regenerative medicine that may be harnessed to address some diseases of prematurity. This is particularly true when the underlying cause of disease is inflammation, immune dysregulation or fibrosis. Owing to the diversity of stem/progenitor cells that can be used in treating diseases of prematurity, their mechanisms of action can be equally diverse (summarized in Figure 2). Stem and stem-like cells derived from gestational tissues are particularly appealing, especially pMSCs and hAECs, which are relatively easy to be isolated in sufficiently large numbers for clinical use, exhibit low antigenicity and have stable telomere lengths without evidence of tumor formation. Although research findings indicate that hAECs and pMSCs have anti-inflammatory, anti-fibrotic and angiogenic effects, further characterization of these cells is required to determine stem cell behavior in various disease settings and organ/ tissue-specific effects. Certainly stem cell efficacy across gestational ages should be determined, regardless of its tissue of origin. This has profound implications on both autologous stem cell banking and the use of autologous versus allogeneic stem cells in an extremely vulnerable patient population.

Disclosure of interests: The authors have no commercial, proprietary, or financial interest in the products or companies described in this article. References 1. WHO. International Statistical Classification of Diseases and Related Health Problems, Tenth Revision: Introduction; list of three-character categories; tabular list of inclusions and four-character subcategories; morphology of neoplams; special tabulation lists for mortality and morbidity; definitions; regulations. World Health Organization; Geneva, Switzerland, 1992. 2. Blencowe H, Cousens S, Oestergaard MZ, Chou D, Moller A-B, Narwal R, et al. National, regional, and worldwide estimates of preterm birth rates in the year 2010 with time trends since 1990 for selected countries: a systematic analysis and implications. Lancet. 2012;379:2162e72. 3. Santos IS, Matijasevich A, Silveira MF, Sclowitz IKT, Barros AJD, Victora CG, et al. Associated factors and consequences of late preterm births: results from the 2004 Pelotas birth cohort. Paediatr Perinat Epidemiol. 2008;22: 350e9. 4. McIntire DD, Leveno KJ. Neonatal mortality and morbidity rates in late preterm births compared with births at term. Obstet Gynecol. 2008;111:35e41. 5. Stoll BJ, Hansen NI, Bell EF, Shankaran S, Laptook AR, Walsh MC, et al. Neonatal outcomes of extremely preterm infants from the NICHD Neonatal Research Network. Pediatrics. 2010;126:443e56.

Cell-based therapies for the preterm infant 6. Khashu M, Narayanan M, Bhargava S, Osiovich H. Perinatal outcomes associated with preterm birth at 33 to 36 weeks’ gestation: a population-based cohort study. Pediatrics. 2009; 123:109e13. 7. Jobe AH. The new bronchopulmonary dysplasia. Curr Opin Pediatr. 2011;22:1e20. 8. Dammann O, Leviton A, Gappa M, Dammann CE. Lung and brain damage in preterm newborns, and their association with gestational age, prematurity subgroup, infection/inflammation and long term outcome. BJOG. 2005; 112(Suppl 1):4e9. 9. Schmolzer GM, Kumar M, Pichler G, Aziz K, O’Reilly M, Cheung PY. Non-invasive versus invasive respiratory support in preterm infants at birth: systematic review and meta-analysis. BMJ. 2013 Oct 17;347:f5980. Doi: 10.1136/bmj.f5980. 10. Tang S, Zhao J, Shen J, Hu Z, Shi Y. Nasal intermittent positive pressure ventilation versus nasal continuous positive airway pressure in neonates: a systematic review and metaanalysis. Indian Pediatr. 2013;50:371e6. 11. Vento M, Moro M, Escrig R, Arruza L, Villar G, Izquierdo I, et al. Preterm resuscitation with low oxygen causes less oxidative stress, inflammation, and chronic lung disease. Pediatrics. 2009;124:e439e49. 12. Fortes Filho JB, Eckert GU, Tartarella MB, Procianoy RS. Prevention of retinopathy of prematurity. Arq Bras Oftalmol. 2011;74:217e21. 13. Sharma R, Hudak ML. A clinical perspective of necrotizing enterocolitis: past, present, and future. Clin Perinatol. 2013; 40:27e51. 14. Wheeler KI, Klingenberg C, Morley CJ, Davis PG. Volumetargeted versus pressure-limited ventilation for preterm infants: a systematic review and meta-analysis. Neonatology. 2011;100:219e27. 15. Fischer HS, Buhrer C. Avoiding endotracheal ventilation to prevent bronchopulmonary dysplasia: a meta-analysis. Pediatrics. 2013;132:e1351e60. 16. Speer CP, Sweet DG, Halliday HL. Surfactant therapy: past, present and future. Early Hum Dev. 2013;89(Suppl 1):S22e4. 17. Halliday HL, Ehrenkranz RA, Doyle LW. Late (>7 days) postnatal corticosteroids for chronic lung disease in preterm infants. Cochrane Database Syst Rev. 2009;1:CD001145. 18. Halliday HL, Ehrenkranz RA, Doyle LW. Early (<8 days) postnatal corticosteroids for preventing chronic lung disease in preterm infants. Cochrane Database Syst Rev. 2010;1: CD001146. 19. Henderson-Smart DJ, Davis PG. Prophylactic methylxanthines for endotracheal extubation in preterm infants. Cochrane Database Syst Rev. 2010;12:CD000139. 20. Schmidt B, Roberts RS, Davis P, Doyle LW, Barrington KJ, Ohlsson A, et al. Caffeine therapy for apnea of prematurity. N Engl J Med. 2006;354:2112e21. 21. Onland W, Offringa M, van Kaam A. Late (7 days) inhalation corticosteroids to reduce bronchopulmonary dysplasia in preterm infants. Cochrane Database Syst Rev. 2012;4: CD002311. 22. McCrea HJ, Ment LR. The diagnosis, management, and postnatal prevention of intraventricular hemorrhage in the preterm neonate. Clin Perinatol. 2008;35:777e92. 23. Ballabh P. Intraventricular hemorrhage in premature infants: mechanism of disease. Pediatr Res. 2010;67:1e8. 24. Deng W, Pleasure J, Pleasure D. Progress in periventricular leukomalacia. Arch Neurol. 2008;65:1291e5. 25. Whitelaw A, Odd D. Postnatal phenobarbital for the prevention of intraventricular hemorrhage in preterm infants. Cochrane Database Syst Rev. 2007;4:CD001691. 26. Jones LJ, Craven PD, Attia J, Thakkinstian A, Wright I. Network meta-analysis of indomethacin versus ibuprofen

27.

28.

29.

30.

31. 32.

33. 34. 35.

36.

37. 38. 39.

40.

41.

42.

43.

44.

45. 46.

11

versus placebo for PDA in preterm infants. Arch Dis Child Fetal Neonatal Ed. 2011;96:F45e52. Schnabl K-L, Van Aerde J-E, Thomson A-B, Clandinin M-T. Necrotizing enterocolitis: a multifactorial disease with no cure. World J Gastroenterol. 2008;14:2142e61. De La Torre CA, Miguel M, Martinez L, Aguilar R, Barrena S, Lassaletta L, et al. [The risk of necrotizing enterocolitis in newborns with congenital heart disease: a single institution-cohort study]. Cir Pediatr. 2010;23:103e6. Neu J, Mihatsch W. Recent developments in necrotizing enterocolitis. JPEN J Parenter Enteral Nutr. 2012;36(Suppl 1):30Se5S. Sharma R, Tepas JJ 3rd. Microecology, intestinal epithelial barrier and necrotizing enterocolitis. Pediatr Surg Int. 2010; 26:11e21. Neu J, Walker WA. Necrotizing enterocolitis. N Engl J Med. 2011;364:255e64. Gordon P, Christensen R, Weitkamp JH, Maheshwari A. Mapping the new world of necrotizing enterocolitis (NEC): review and opinion. The e-journal of Neonatol Res. 2012;2: 145e72. Lin PW, Stoll BJ. Necrotising enterocolitis. Lancet. 2006; 368:1271e83. Neu J. Routine probiotics for premature infants: let’s be careful! J Pediatr. 2011;158:672e4. Fortes Filho JB, Eckert GU, Procianoy L, Barros CK, Procianoy RS. Incidence and risk factors for retinopathy of prematurity in very low and in extremely low birth weight infants in a unit-based approach in southern Brazil. Eye. 2007;23:25e30. Niranjan HS, Benakappa N, Reddy KB, Nanda S, Kamath MV. Retinopathy of prematurity promising newer modalities of treatment. Indian Pediatr. 2012;49:139e43. Mintz-Hittner HA. Avastin as monotherapy for retinopathy of prematurity. J AAPOS. 2010;14:2e3. Doyle LW, Anderson PJ. Adult outcome of extremely preterm infants. Pediatrics. 2010;126:342e51. de Jong F, Monuteaux MC, van Elburg RM, Gillman MW, Belfort MB. Systematic review and meta-analysis of preterm birth and later systolic blood pressure. Hypertension. 2012; 59:226e34. Paavonen EJ, Strang-Karlsson S, Raikkonen K, Heinonen K, Pesonen AK, Hovi P, et al. Very low birth weight increases risk for sleep-disordered breathing in young adulthood: the Helsinki Study of Very Low Birth Weight Adults. Pediatrics. 2007;120:778e84. Mathiasen R, Hansen BM, Nybo Anderson AM, Greisen G. Socio-economic achievements of individuals born very preterm at the age of 27 to 29 years: a nationwide cohort study. Dev Med Child Neurol. 2009;51:901e8. Mwaniki MK, Atieno M, Lawn JE, Newton CR. Long-term neurodevelopmental outcomes after intrauterine and neonatal insults: a systematic review. Lancet. 2012;379: 445e52. Lindstrom K, Lindblad F, Hjern A. Psychiatric morbidity in adolescents and young adults born preterm: a Swedish national cohort study. Pediatrics. 2009;123:e47e53. Ghosh Z, Huang M, Hu S, Wilson KD, Dey D, Wu JC. Dissecting the oncogenic and tumorigenic potential of differentiated human induced pluripotent stem cells and human embryonic stem cells. Cancer Res. 2011;71:5030e9. Lu X, Zhao T. Clinical therapy using iPSCs: hopes and challenges. Genom Proteom Bioinform. 2013;11:294e8. Moretti A, Bellin M, Welling A, Jung CB, Lam JT, BottFlugel L, et al. Patient-specific induced pluripotent stem-cell models for long-QT syndrome. N Engl J Med. 2010;363: 1397e409.

12

D. Zhu et al.

47. Kim C, Wong J, Wen J, Wang S, Wang C, Spiering S, et al. Studying arrhythmogenic right ventricular dysplasia with patient-specific iPSCs. Nature. 2013;494:105e10. 48. Lu TY, Lin B, Kim J, Sullivan M, Tobita K, Salama G, et al. Repopulation of decellularized mouse heart with human induced pluripotent stem cell-derived cardiovascular progenitor cells. Nature Commun. 2013;4:2307. 49. Hanna J, Wernig M, Markoulaki S, Sun CW, Meissner A, Cassady JP, et al. Treatment of sickle cell anemia mouse model with iPS cells generated from autologous skin. Science. 2007;318:1920e3. 50. Gluckman E, Broxmeyer HA, Auerbach AD, Friedman HS, Douglas GW, Devergie A, et al. Hematopoietic reconstitution in a patient with Fanconi’s anemia by means of umbilical-cord blood from an HLA-identical sibling. N Engl J Med. 1989;321:1174e8. 51. Almici C, Carlo-Stella C, Wagner JE, Rizzoli V. Umbilical cord blood as a source of hematopoietic stem cells: from research to clinical application. Haematologica. 1995;80: 473e9. 52. Bradley MB, Cairo MS. Cord blood immunology and stem cell transplantation. Hum Immunol. 2005;66:431e46. 53. Badowski MS, Harris DT. Collection, processing, and banking of umbilical cord blood stem cells for transplantation and regenerative medicine. Methods Mol Biol. 2012;879: 279e90. doi: 10.1007/978-1-61779-815-3_16. 54. Hollands P. Cord blood stem cells: the basic science. In: Bhattacharya N, Stubblefield PG. Frontiers of Cord Blood Science. 1st edition. Springer, London; 2009. p. 21. 55. Ende N, Lu S, Alcid MG, Chen R, Mack R. Pooled umbilical cord blood as a possible universal donor for marrow reconstitution and use in nuclear accidents. Life Sci. 2001; 69:1531e9. 56. Tiwari A, Tursky ML, Mushahary D, Wasnik S, Collier FM, Suma K, et al. Ex vivo expansion of haematopoietic stem/ progenitor cells from human umbilical cord blood on acellular scaffolds prepared from MS-5 stromal cell line. J Tissue Eng Regen Med. 2013;7:871e83. 57. Delaney C, Heimfeld S, Brashem-Stein C, Voorhies H, Manger RL, Bernstein ID. Notch-mediated expansion of human cord blood progenitor cells capable of rapid myeloid reconstitution. Nat Med. 2010;16:232e6. 58. Naruse K, Hamada Y, Nakashima E, Kato K, Mizubayashi R, Kamiya H, et al. Therapeutic neovascularization using cord blood-derived endothelial progenitor cells for diabetic neuropathy. Diabetes. 2005;54: 1823e8. 59. Phuc PV, Ngoc VB, Lam DH, Tam NT, Viet PQ, Ngoc PK. Isolation of three important types of stem cells from the same samples of banked umbilical cord blood. Cell Tissue Bank. 2012;13:341e51. 60. Rookmaaker MB, Vergeer M, van Zonneveld AJ, Rabelink TJ, Verhaar MC. Endothelial progenitor cells: mainly derived from the monocyte/macrophage-containing CD34- mononuclear cell population and only in part from the hematopoietic stem cell-containing CD34þ mononuclear cell population. Circulation. 2003;108:e150. 61. Yoder MC. Human endothelial progenitor cells. Cold Spring Harb Perspect Med. 2012;2:a006692. 62. Coldwell KE, Lee SJ, Kean J, Khoo CP, Tsaknakis G, Smythe J, et al. Effects of obstetric factors and storage temperatures on the yield of endothelial colony forming cells from umbilical cord blood. Angiogenesis. 2011;14:381e92. 63. Reinisch A, Hofmann NA, Obenauf AC, Kashofer K, Rohde E, Schallmoser K, et al. Humanized large-scale expanded endothelial colony-forming cells function in vitro and in vivo. Blood. 2009;113:6716e25.

64. Hermansen SE, Lund T, Kalstad T, Ytrehus K, Myrmel T. Adrenomedullin augments the angiogenic potential of late outgrowth endothelial progenitor cells. Am J Physiol Cell Physiol. 2011;300:C783e91. 65. Baker CD, Seedorf GJ, Wisniewski BL, Black CP, Ryan SL, Balasubramaniam V, et al. Endothelial colony-forming cell conditioned media promote angiogenesis in vitro and prevent pulmonary hypertension in experimental bronchopulmonary dysplasia. Am J Physiol Lung Cell Mol Physiol. 2013;305: L73e81. 66. Zhang Y, Li Y, Wang S, Han Z, Huang X, Li S, et al. Transplantation of expanded endothelial colony-forming cells improved outcomes of traumatic brain injury in a mouse model. J Surg Res. 2013;185:441e9. 67. Romanov YA, Svintsitskaya VA, Smirnov VN. Searching for alternative sources of postnatal human mesenchymal stem cells: candidate MSC-like cells from umbilical cord. Stem Cells. 2003;21:105e10. 68. Lee OK, Kuo TK, Chen WM, Lee KD, Hsieh SL, Chen TH. Isolation of multipotent mesenchymal stem cells from umbilical cord blood. Blood. 2004;103:1669e75. 69. Portmann-Lanz CB, Schoeberlein A, Huber A, Sager R, Malek A, Holzgreve W, et al. Placental mesenchymal stem cells as potential autologous graft for pre- and perinatal neuroregeneration. Am J Obstet Gynecol. 2006;194:664e73. 70. Kern S, Eichler H, Stoeve J, Kluter H, Bieback K. Comparative analysis of mesenchymal stem cells from bone marrow, umbilical cord blood, or adipose tissue. Stem Cells. 2006;24:1294e301. 71. Batsali AK, Kastrinaki MC, Papadaki HA, Pontikoglou C. Mesenchymal stem cells derived from Wharton’s jelly of the umbilical cord: biological properties and emerging clinical applications. Curr Stem Cell Res Ther. 2013;8:144e55. 72. Gargett CE, Schwab KE, Zillwood RM, Nguyen HP, Wu D. Isolation and culture of epithelial progenitors and mesenchymal stem cells from human endometrium. Biol Reprod. 2009;80:1136e45. 73. Brooke G, Rossetti T, Pelekanos R, Ilic N, Murray P, Hancock S, et al. Manufacturing of human placenta-derived mesenchymal stem cells for clinical trials. Br J Haematol. 2009;144:571e9. 74. Tsai M-S, Hwang S-M, Chen K-D, Lee Y-S, Hsu L-W, Chang Y-J, et al. Functional network analysis of the transcriptomes of mesenchymal stem cells derived from amniotic fluid, amniotic membrane, cord blood, and bone marrow. Stem Cells. 2007;25:2511e23. 75. Miao Z, Jin J, Chen L, Zhu J, Huang W, Zhao J, et al. Isolation of mesenchymal stem cells from human placenta: comparison with human bone marrow mesenchymal stem cells. Cell Biol Int. 2006;30:681e7. 76. Laitinen A, Laine J. Isolation of mesenchymal stem cells from human cord blood. Curr Protoc Stem Cell Biol. 2007;2:2A3. 77. Zhang X, Hirai M, Cantero S, Ciubotariu R, Dobrila L, Hirsh A, et al. Isolation and characterization of mesenchymal stem cells from human umbilical cord blood: reevaluation of critical factors for successful isolation and high ability to proliferate and differentiate to chondrocytes as compared to mesenchymal stem cells from bone marrow and adipose tissue. J Cell Biochem. 2011;112:1206e18. 78. Sibov TT, Severino P, Marti LC, Pavon LF, Oliveira DM, Tobo PR, et al. Mesenchymal stem cells from umbilical cord blood: parameters for isolation, characterization and adipogenic differentiation. Cytotechnology. 2012;64:511e21. 79. Chang YS, Ahn SY, Yoo HS, Sung SI, Choi SJ, Oh WI, et al. Mesenchymal stem cells for bronchopulmonary dysplasia: phase 1 dose-escalation clinical trial. J Pediatr. 2014;164: 966e72.

Cell-based therapies for the preterm infant 80. Steigman SA, Fauza DO. Isolation of mesenchymal stem cells from amniotic fluid and placenta. Curr Protoc Stem Cell Biol. 2007;1:1E2. 81. Tsai MS, Lee JL, Chang YJ, Hwang SM. Isolation of human multipotent mesenchymal stem cells from second-trimester amniotic fluid using a novel two-stage culture protocol. Hum Reprod. 2004;19:1450e6. 82. Wang HS, Hung SC, Peng ST, Huang CC, Wei HM, Guo YJ, et al. Mesenchymal stem cells in the Wharton’s jelly of the human umbilical cord. Stem Cells. 2004;22:1330e7. 83. Salehinejad P, Alitheen NB, Ali AM, Omar AR, Mohit M, Janzamin E, et al. Comparison of different methods for the isolation of mesenchymal stem cells from human umbilical cord Wharton’s jelly. In Vitro Cell Dev Biol Anim. 2012;48: 75e83. 84. Steigman SA, Armant M, Bayer-Zwirello L, Kao GS, Silberstein L, Ritz J, et al. Preclinical regulatory validation of a 3-stage amniotic mesenchymal stem cell manufacturing protocol. J Pediatr Surg. 2008;43:1164e9. 85. Yoon JH, Roh EY, Shin S, Jung NH, Song EY, Chang JY, et al. Comparison of explant-derived and enzymatic digestion-derived MSCs and the growth factors from Wharton’s jelly. BioMed Res Int. 2013;2013:428726. 86. Soncini M, Vertua E, Gibelli L, Zorzi F, Denegri M, Albertini A, et al. Isolation and characterization of mesenchymal cells from human fetal membranes. J Tissue Eng Regen Med. 2007;1:296e305. 87. Moore RM, Silver RJ, Moore JJ. Physiological apoptotic agents have different effects upon human amnion epithelial and mesenchymal cells. Placenta. 2003;24:173e80. 88. Casey ML, MacDonald PC. Interstitial collagen synthesis and processing in human amnion: a property of the mesenchymal cells. Biol Reprod. 1996;55:1253e60. 89. Parolini O, Alviano F, Bagnara GP, Bilic G, Bühring H-J, Evangelista M, et al. Concise review: isolation and characterization of cells from human term placenta: outcome of the first international workshop on placenta derived stem cells. Stem Cells. 2008;26:300e11. 90. Murphy S, Rosli S, Acharya R, Mathias L, Lim R, Wallace E, et al. Amnion epithelial cell isolation and characterization for clinical use. Curr Protoc Stem Cell Biol. 2010;1:1E6. 91. Ilancheran S, Michalska A, Peh G, Wallace EM, Pera M, Manuelpillai U. Stem cells derived from human fetal membranes display multilineage differentiation potential. Biol Reprod. 2007;77:577e88. 92. Lim R, Chan ST, Tan JL, Mockler JC, Murphy SV, Wallace EM. Preterm human amnion epithelial cells have limited reparative potential. Placenta. 2013;34:486e92. 93. Li H, Niederkorn JY, Neelam S, Mayhew E, Word RA, McCulley JP, et al. Immunosuppressive factors secreted by human amniotic epithelial cells. Invest Ophthalmol Vis Sci. 2005;46:900e7. 94. Wolbank S, Peterbauer A, Fahrner M, Hennerbichler S, van Griensven M, Stadler G, et al. Dose-dependent immunomodulatory effect of human stem cells from amniotic membrane: a comparison with human mesenchymal stem cells from adipose tissue. Tissue Eng. 2007;13:1173e83. 95. Diaz-Prado S, Muinos-Lopez E, Hermida-Gomez T, Rendal-Vazquez ME, Fuentes-Boquete I, de Toro FJ, et al. Multilineage differentiation potential of cells isolated from the human amniotic membrane. J Cell Biochem. 2010;111: 846e57. 96. Bilic G, Zeisberger SM, Mallik AS, Zimmermann R, Zisch AH. Comparative characterization of cultured human term amnion epithelial and mesenchymal stromal cells for application in cell therapy. Cell Transplant. 2008;17: 955e68.

13

97. Niwa H, Masui S, Chambers I, Smith AG, Miyazaki J. Phenotypic complementation establishes requirements for specific POU domain and generic transactivation function of Oct-3/4 in embryonic stem cells. Mol Cell Biol. 2002;22: 1526e36. 98. Trounson A, Pera M. Human embryonic stem cells. Fertil Steril. 2001;76:660e1. 99. Díaz-Prado S, Muiños-López E, Hermida-Gómez T, Cicione C, Rendal-Vázquez ME, Fuentes-Boquete I, et al. Human amniotic membrane as an alternative source of stem cells for regenerative medicine. Differentiation. 2011;81: 162e71. 100. Yang X, Song L, Wu N, Liu Z, Xue S, Hui G. An experimental study on intracerebroventricular transplantation of human amniotic epithelial cells in a rat model of Parkinson’s disease. Neurol Res. 2010;32:1054e9. 101. Kakishita K, Elwan MA, Nakao N, Itakura T, Sakuragawa N. Human amniotic epithelial cells produce dopamine and survive after implantation into the striatum of a rat model of Parkinson’s disease: a potential source of donor for transplantation therapy. Exp Neurol. 2000;165: 27e34. 102. Manuelpillai U, Tchongue J, Lourensz D, Vaghjiani V, Samuel CS, Liu A, et al. Transplantation of human amnion epithelial cells reduces hepatic fibrosis in immunocompetent CCl(4)-treated mice. Cell Transplant. 2010;19:1157e68. 103. Hou Y, Huang Q, Liu T, Guo L. Human amnion epithelial cells can be induced to differentiate into functional insulinproducing cells. Acta Biochim Biophys Sinica. 2008;40: 830e9. 104. Hodges RJ, Jenkin G, Hooper SB, Allison B, Lim R, Dickinson H, et al. Human amnion epithelial cells reduce ventilation-induced preterm lung injury in fetal sheep. Am J Obstet Gynecol. 2012;206:448. e8ee15. 105. Wei JP, Zhang TS, Kawa S, Aizawa T, Ota M, Akaike T, et al. Human amnion-isolated cells normalize blood glucose in streptozotocin-induced diabetic mice. Cell Transplant. 2003;12:545e52. 106. In’t Anker PS, Scherjon SA, Kleijburg-van der Keur C, de Groot-Swings GMJS, Claas FHJ, Fibbe WE, et al. Isolation of mesenchymal stem cells of fetal or maternal origin from human placenta. Stem Cells. 2004;22:1338e45. 107. Sakuragawa N, Kakinuma K, Kikuchi A, Okano H, Uchida S, Kamo I, et al. Human amnion mesenchyme cells express phenotypes of neuroglial progenitor cells. J Neurosci Res. 2004;78:208e14. 108. Alviano F, Fossati V, Marchionni C, Arpinati M, Bonsi L, Franchina M, et al. Term amniotic membrane is a high throughput source for multipotent mesenchymal stem cells with the ability to differentiate into endothelial cells in vitro. BMC Dev Biol. 2007;7:11. 109. Zhao P, Ise H, Hongo M, Ota M, Konishi I, Nikaido T. Human amniotic mesenchymal cells have some characteristics of cardiomyocytes. Transplantation. 2005;79:528e35. 110. Zhang X, Mitsuru A, Igura K, Takahashi K, Ichinose S, Yamaguchi S, et al. Mesenchymal progenitor cells derived from chorionic villi of human placenta for cartilage tissue engineering. Biochem Biophys Res Commun. 2006;340: 944e52. 111. Wei JP, Nawata M, Wakitani S, Kametani K, Ota M, Toda A, et al. Human amniotic mesenchymal cells differentiate into chondrocytes. Cloning Stem Cells. 2009;11: 19e26. 112. Tan JL, Chan ST, Wallace EM, Lim R. Human amnion epithelial cells mediate lung repair by directly modulating macrophage recruitment and polarization. Cell Transplant. 2014 Mar;23(3):319e28.

14

D. Zhu et al.

113. Carraro G, Perin L, Sedrakyan S, Giuliani S, Tiozzo C, Lee J, et al. Human amniotic fluid stem cells can integrate and differentiate into epithelial lung lineages. Stem Cells. 2008;26:2902e11. 114. Liu YH, Vaghjiani V, Tee JY, To K, Cui P, Oh DY, et al. Amniotic epithelial cells from the human placenta potently suppress a mouse model of multiple sclerosis. PLoS One. 2012;7:e35758. 115. Kamiya K, Wang M, Uchida S, Amano S, Oshika T, Sakuragawa N, et al. Topical application of culture supernatant from human amniotic epithelial cells suppresses inflammatory reactions in cornea. Exp Eye Res. 2005;80: 671e9. 116. Murphy S, Lim R, Dickinson H, Acharya R, Rosli S, Jenkin G, et al. Human amnion epithelial cells prevent bleomycin-induced lung injury and preserve lung function. Cell Transplant. 2011;20:909e23. 117. Vosdoganes P, Hodges RJ, Lim R, Westover AJ, Acharya RY, Wallace EM, et al. Human amnion epithelial cells as a treatment for inflammation-induced fetal lung injury in sheep. Am J Obstet Gynecol. 2011;205:156. e26e33. 118. Murphy SV, Shiyun SC, Tan JL, Chan S, Jenkin G, Wallace EM, et al. Human amnion epithelial cells do not abrogate pulmonary fibrosis in mice with impaired macrophage function. Cell Transplant. 2012;21:1477e92. 119. Hwang JH, Shim SS, Seok OS, Lee HY, Woo SK, Kim BH, et al. Comparison of cytokine expression in mesenchymal stem cells from human placenta, cord blood, and bone marrow. J Korean Med Sci. 2009;24:547e54. 120. Galindo LT, Filippo TRM, Semedo P, Ariza CB, Moreira CM, Camara NOS, et al. Mesenchymal stem cell therapy modulates the inflammatory response in experimental traumatic brain injury. Neurol Res Int. 2011;2011: 564089. 121. Semedo P, Palasio CG, Oliveira CD, Feitoza CQ, Gonçalves GM, Cenedeze MA, et al. Early modulation of inflammation by mesenchymal stem cell after acute kidney injury. Int Immunopharmacol. 2009;9:677e82. 122. Di Nicola M, Carlo-Stella C, Magni M, Milanesi M, Longoni PD, Matteucci P, et al. Human bone marrow stromal cells suppress T-lymphocyte proliferation induced by cellular or nonspecific mitogenic stimuli. Blood. 2002;99: 3838e43. 123. Liu WH, Liu JJ, Wu J, Zhang LL, Liu F, Yin L, et al. Novel mechanism of inhibition of dendritic cells maturation by mesenchymal stem cells via interleukin-10 and the JAK1/ STAT3 signaling pathway. PLoS One. 2013;8:e55487. 124. Jiang XX, Zhang Y, Liu B, Zhang SX, Wu Y, Yu XD, et al. Human mesenchymal stem cells inhibit differentiation and function of monocyte-derived dendritic cells. Blood. 2005; 105:4120e6. 125. Corcione A, Benvenuto F, Ferretti E, Giunti D, Cappiello V, Cazzanti F, et al. Human mesenchymal stem cells modulate B-cell functions. Blood. 2006;107:367e72. 126. Li W, He H, Chen YT, Hayashida Y, Tseng SC. Reversal of myofibroblasts by amniotic membrane stromal extract. J Cell Physiol. 2008;215:657e64. 127. Vosdoganes P, Wallace EM, Chan ST, Acharya R, Moss TJ, Lim R. Human amnion epithelial cells repair established lung injury. Cell Transplant. 2013;22:1337e49. 128. Moodley Y, Ilancheran S, Samuel C, Vaghjiani V, Atienza D, Williams ED, et al. Human amnion epithelial cell transplantation abrogates lung fibrosis and augments repair. Am J Respir Crit Care Med. 2010;182:643e51. 129. Manuelpillai U, Lourensz D, Vaghjiani V, Tchongue J, Lacey D, Tee J-Y, et al. Human amniotic epithelial cell

130.

131.

132.

133.

134.

135.

136.

137.

138.

139.

140.

141.

142.

143.

144.

145.

146.

transplantation induces markers of alternative macrophage activation and reduces established hepatic fibrosis. PLoS One. 2012;7:e38631. Moodley Y, Atienza D, Manuelpillai U, Samuel CS, Tchongue J, Ilancheran S, et al. Human umbilical cord mesenchymal stem cells reduce fibrosis of bleomycininduced lung injury. Am J Pathol. 2009;175:303e13. Ortiz LA, Dutreil M, Fattman C, Pandey AC, Torres G, Go K, et al. Interleukin 1 receptor antagonist mediates the antiinflammatory and antifibrotic effect of mesenchymal stem cells during lung injury. Proc Natl Acad Sci U S A. 2007;104:11002e7. Rabani V, Shahsavani M, Gharavi M, Piryaei A, Azhdari Z, Baharvand H. Mesenchymal stem cell infusion therapy in a carbon tetrachloride-induced liver fibrosis model affects matrix metalloproteinase expression. Cell Biol Int. 2010;34:601e5. Mias C, Lairez O, Trouche E, Roncalli J, Calise D, Seguelas MH, et al. Mesenchymal stem cells promote matrix metalloproteinase secretion by cardiac fibroblasts and reduce cardiac ventricular fibrosis after myocardial infarction. Stem Cells. 2009;27:2734e43. Li L, Zhang Y, Li Y, Yu B, Xu Y, Zhao S, et al. Mesenchymal stem cell transplantation attenuates cardiac fibrosis associated with isoproterenol-induced global heart failure. Transpl Int. 2008;21:1181e9. Wolbank S, Hildner F, Redl H, van Griensven M, Gabriel C, Hennerbichler S. Impact of human amniotic membrane preparation on release of angiogenic factors. J Tissue Eng Regen Med. 2009;3:651e4. Steed DL, Trumpower C, Duffy D, Smith C, Marshall V, Rupp R, et al. Amnion-derived cellular cytokine solution: a physiological combination of cytokines for wound healing. Eplasty. 2008;8:e18. Niknejad H, Paeini-Vayghan G, Tehrani FA, KhayatKhoei M, Peirovi H. Side dependent effects of the human amnion on angiogenesis. Placenta. 2013;34:340e5. Maxson S, Lopez EA, Yoo D, Danilkovitch-Miagkova A, Leroux MA. Concise review: role of mesenchymal stem cells in wound repair. Stem Cells Translat Med. 2012;1:142e9. Oh JY, Kim MK, Shin MS, Lee HJ, Ko JH, Wee WR, et al. The anti-inflammatory and anti-angiogenic role of mesenchymal stem cells in corneal wound healing following chemical injury. Stem Cells. 2008;26:1047e55. Hori J, Wang M, Kamiya K, Takahashi H, Sakuragawa N. Immunological characteristics of amniotic epithelium. Cornea. 2006;25(10 Suppl 1):S53e8. Watkins DJ, Yang J, Matthews MA, Besner GE. Synergistic effects of HB-EGF and mesenchymal stem cells in a murine model of intestinal ischemia/reperfusion injury. J Pediatr Surg. 2013;48:1323e9. Zhu XY, Lerman A, Lerman LO. Concise review: mesenchymal stem cell treatment for ischemic kidney disease. Stem Cells. 2013 Sep;31(9):1731e6. Martinez-Gonzalez I, Moreno R, Petriz J, Gratacos E, Aran JM. Engraftment potential of adipose tissue-derived human mesenchymal stem cells after transplantation in the fetal rabbit. Stem Cells Dev. 2012;21:3270e7. Sakuragawa N, Enosawa S, Ishii T, Thangavel R, Tashiro T, Okuyama T, et al. Human amniotic epithelial cells are promising transgene carriers for allogeneic cell transplantation into liver. J Hum Genet. 2000;45:171e6. Bailo M, Soncini M, Vertua E, Signoroni PB, Sanzone S, Lombardi G, et al. Engraftment potential of human amnion and chorion cells derived from term placenta. Transplantation. 2004;78:1439e48. Cargnoni A, Gibelli L, Tosini A, Signoroni PB, Nassuato C, Arienti D, et al. Transplantation of allogeneic and

Cell-based therapies for the preterm infant

147.

148.

149.

150.

151.

152.

153.

154.

155.

156.

157.

158.

159.

160.

161.

162.

xenogeneic placenta-derived cells reduces bleomycininduced lung fibrosis. Cell Transplant. 2009;18:405e22. Pierro M, Ionescu L, Montemurro T, Vadivel A, Weissmann G, Oudit G, et al. Short-term, long-term and paracrine effect of human umbilical cord-derived stem cells in lung injury prevention and repair in experimental bronchopulmonary dysplasia. Thorax. 2013;68:475e84. Kim JW, Ha KY, Molon JN, Kim YH. Bone marrow-derived mesenchymal stem cell transplantation for chronic spinal cord injury in rats: comparative study between intralesional and intravenous transplantation. Spine. 2013;38:E1065e74. Tropea KA, Leder E, Aslam M, Lau AN, Raiser DM, Lee JH, et al. Bronchioalveolar stem cells increase after mesenchymal stromal cell treatment in a mouse model of bronchopulmonary dysplasia. Am J Physiol Lung Cell Mol Physiol. 2012;302:L829e37. Yawno T, Schuilwerve J, Moss TJM, Vosdoganes P, Westover AJ, Afandi E, et al. Human amnion epithelial cells reduce fetal brain injury in response to intrauterine inflammation. Dev Neurosci. 2013;35(2-3):272e82. Aslam M, Baveja R, Liang OD, Fernandez-Gonzalez A, Lee C, Mitsialis SA, et al. Bone marrow stromal cells attenuate lung injury in a murine model of neonatal chronic lung disease. Am J Respir Crit Care Med. 2009;180:1122e30. Roccaro AM, Sacco A, Maiso P, Azab AK, Tai YT, Reagan M, et al. BM mesenchymal stromal cell-derived exosomes facilitate multiple myeloma progression. J Clin Invest. 2013;123:1542e55. Lai RC, Tan SS, Teh BJ, Sze SK, Arslan F, de Kleijn DP, et al. Proteolytic potential of the MSC exosome proteome: implications for an exosome-mediated delivery of therapeutic proteasome. Int J Proteom. 2012;2012:971907. Valadi H, Ekstrom K, Bossios A, Sjostrand M, Lee JJ, Lotvall JO. Exosome-mediated transfer of mRNAs and microRNAs is a novel mechanism of genetic exchange between cells. Nat Cell Biol. 2007;9:654e9. Lee C, Mitsialis SA, Aslam M, Vitali SH, Vergadi E, Konstantinou G, et al. Exosomes mediate the cytoprotective action of mesenchymal stromal cells on hypoxia-induced pulmonary hypertension. Circulation. 2012;126:2601e11. Liu T, Wu J, Huang Q, Hou Y, Jiang Z, Zang S, et al. Human amniotic epithelial cells ameliorate behavioral dysfunction and reduce infarct size in the rat middle cerebral artery occlusion model. Shock. 2008;29:603e11. Qureshi KM, Oliver RJ, Paget MB, Murray HE, Bailey CJ, Downing R. Human amniotic epithelial cells induce localized cell-mediated immune privilege in vitro: implications for pancreatic islet transplantation. Cell Transplant. 2011;20: 523e34. Dong W, Chen H, Yang X, Guo L, Hui G. Treatment of intracerebral haemorrhage in rats with intraventricular transplantation of human amniotic epithelial cells. Cell Biol Int. 2010;34:573e7. Sankar V, Muthusamy R. Role of human amniotic epithelial cell transplantation in spinal cord injury repair research. Neuroscience. 2003;118:11e7. Wu ZY, Hui GZ, Lu Y, Wu X, Guo LH. Transplantation of human amniotic epithelial cells improves hindlimb function in rats with spinal cord injury. Chin Med J. 2006;119:2101e7. Venkatachalam S, Palaniappan T, Jayapal PK, Neelamegan S, Rajan SS, Muthiah VP. Novel neurotrophic factor secreted by amniotic epithelial cells. Biocell. 2009;33:81e9. van Haaften T, Byrne R, Bonnet S, Rochefort GY, Akabutu J, Bouchentouf M, et al. Airway delivery of mesenchymal stem cells prevents arrested alveolar growth in neonatal lung injury in rats. Am J Respir Crit Care Med. 2009;180:1131e42.

15

163. Chen A, Siow B, Blamire AM, Lako M, Clowry GJ. Transplantation of magnetically labeled mesenchymal stem cells in a model of perinatal brain injury. Stem Cell Res. 2010;5:255e66. 164. Lee JA, Kim BI, Jo CH, Choi CW, Kim EK, Kim HS, et al. Mesenchymal stem-cell transplantation for hypoxic-ischemic brain injury in neonatal rat model. Pediatr Res. 2010;67: 42e6. 165. Kim ES, Chang YS, Choi SJ, Kim JK, Yoo HS, Ahn SY, et al. Intratracheal transplantation of human umbilical cord blood-derived mesenchymal stem cells attenuates Escherichia coli-induced acute lung injury in mice. Respir Res. 2011;12:108. 166. Tayman C, Uckan D, Kilic E, Ulus AT, Tonbul A, Murat Hirfanoglu I, et al. Mesenchymal stem cell therapy in necrotizing enterocolitis: a rat study. Pediatr Res. 2011;70: 489e94. 167. Eaton S, Zani A, Pierro A, De Coppi P. Stem cells as a potential therapy for necrotizing enterocolitis. Expert Opin Biol Ther. 2013;13:1683e9. 168. Kranz A, Wagner DC, Kamprad M, Scholz M. Transplantation of placenta-derived mesenchymal stromal cells upon experimental stroke in rats. Brain Res. 2010;1315:128e36. 169. Tao J, Ji F, Liu B, Wang F, Dong F, Zhu Y. Improvement of deficits by transplantation of lentiviral vector-modified human amniotic mesenchymal cells after cerebral ischemia in rats. Brain Res. 2012;1448:1e10. 170. Hansmann G, Fernandez-Gonzalez A, Aslam M, Vitali SH, Martin T, Mitsialis SA, et al. Mesenchymal stem cellmediated reversal of bronchopulmonary dysplasia and associated pulmonary hypertension. Pulm Circ. 2012;2:170e81. 171. Nakagawa Y, Masuda H, Ito R, Kobori M, Wada M, Shizuno T, et al. Aberrant kinetics of bone marrow-derived endothelial progenitor cells in the murine oxygen-induced retinopathy model. Invest Ophthalmol Vis Sci. 2011;52: 7835e41. 172. Titomanlio L, Bouslama M, Le Verche V, Dalous J, Kaindl AM, Tsenkina Y, et al. Implanted neurospherederived precursors promote recovery after neonatal excitotoxic brain injury. Stem Cells Dev. 2011;20:865e79. 173. Comi AM, Cho E, Mulholland JD, Hooper A, Li Q, Qu Y, et al. Neural stem cells reduce brain injury after unilateral carotid ligation. Pediatr Neurol. 2008;38:86e92. 174. Nonaka M, Yoshikawa M, Nishimura F, Yokota H, Kimura H, Hirabayashi H, et al. Intraventricular transplantation of embryonic stem cell-derived neural stem cells in intracerebral hemorrhage rats. Neurol Res. 2004;26: 265e72. 175. Titomanlio L, Kavelaars A, Dalous J, Mani S, El Ghouzzi V, Heijnen C, et al. Stem cell therapy for neonatal brain injury: perspectives and challenges. Ann Neurol. 2011;70:698e712. 176. Xia G, Hong X, Chen X, Lan F, Zhang G, Liao L. Intracerebral transplantation of mesenchymal stem cells derived from human umbilical cord blood alleviates hypoxic ischemic brain injury in rat neonates. J Perinat Med. 2010; 38:215e21. 177. van Velthoven CT, Kavelaars A, van Bel F, Heijnen CJ. Mesenchymal stem cell treatment after neonatal hypoxicischemic brain injury improves behavioral outcome and induces neuronal and oligodendrocyte regeneration. Brain Behav Immun. 2010;24:387e93. 178. Alphonse RS, Vadivel A, Fung M, Shelley WC, Critser PJ, Ionescu L, et al. Existence, functional impairment, and lung repair potential of endothelial colony-forming cells in oxygen-induced arrested alveolar growth. Circulation. 2014; 129:2144e57.