Amniotic membrane transplantation in ocular surface disorders

Plasma-Treated Electrospun PLGA Nanofiber Scaffold Supports Limbal Stem Cells

The corneal epithelial layer is continuously replaced by limbal stem cells. Reconstructing this layer in vitro using synthetic scaffolds is highly needed. Poly-lactic-co-glycolic acid (PLGA) is approved for human use due to its biocompatibility and biodegradability. However, PLGA is hydrophobic, preventing cell adherence to PLGA membranes. PLGA scaffolds were prepared by electrospinning on a custom-made target drum spinning at a rate of 1000 rpm with a flow rate of 0.5 mL/h and voltage at 20 kV, then treated with oxygen plasma at 30 mA using a vacuum coater. Scaffolds were characterized by SEM, mechanically by tensile testing, and thermally by DSC and TGA. In vitro degradation was measured by weight loss and pH drop. Wettability was assessed through water uptake and contact angles measurements. Human limbal stem cells (hLSCs) were isolated and seeded on the scaffolds. Cell attachment and cytotoxicity assay were evaluated on day 1 and 5 after cell seeding. SEM showed regular fiber morphology with diameters ranging between 150 nm and 950 nm. Tensile strength demonstrated similar average stress values for both plasma- and non-plasma-treated samples. Scaffolds also showed gradual degradability over a period of 7-8 weeks. Water contact angle and water absorption were significantly enhanced for plasma-treated scaffolds, indicating a favorable increase in their hydrophilicity. Scaffolds have also supported hLSCs growth and attachment with no signs of cytotoxicity. We have characterized a nanofiber electrospun plasma-treated PLGA scaffold to investigate the mechanical and biological properties and the ability to support the attachment and maintenance of hLSCs.

Experimental evaluation of safety and efficacy of plasma-treated poly-ε-caprolactone membrane as a substitute for human amniotic membrane in treating corneal epithelial defects in rabbit eyes

Purpose:

To evaluate biocompatibility and safety of plasma-treated poly-ε-caprolactone (pPCL) membrane compared to the human amniotic membrane in the healing of corneal epithelial defects in an experimental model.

Methods:

This is a prospective, randomized animal study including 12 rabbits. Circular epithelial injury measuring 6 mm in diameter was induced over the central cornea of one eye in twelve rabbits. The rabbits were randomized into two groups; in group A, the defect was covered with human amniotic membrane, while in group B, an artificial membrane made of bio-polymer plasma-treated poly-ε-caprolactone was grafted. Six rabbits were euthanized after 1 month and the other six after 3 months and the corneal epithelium was evaluated histopathologically and with immunohistochemistry.

Results:

Light microscopy of the corneal tissue performed after 1 month and 3 months demonstrated similar findings with no significant complications in either group. Immunohistochemistry with anti-CK-3 antibody showed characteristic corneal phenotype in the healed epithelium. In eyes grafted with pPCL membrane, epithelial healing as estimated by a decrease in size of the defect was significantly better than the group treated with the human amniotic membrane at all time periods monitored (P < 0.05), except day 1 (P = 0.83). The percentage reduction in the size of the epithelial defect was also significantly more in the pPCL membrane group as compared to the human amniotic membrane at all time periods (P < 0.05 at all observations) post-implantation except day 1 (P = 0.73).

Conclusion:

Plasma-treated poly-ε-caprolactone membrane is safe, biocompatible, and effective in the healing of corneal epithelial defects in rabbits.

Insights on the Human Amniotic Membrane in Clinical Practice with a Focus on the New Applications in Retinal Surgery

Recently, the use of the human amniotic membrane (hAM) has been extended to treat retinal disorders such as refractory macular holes, retinal breaks and dry and wet age-related macular degeneration. Not only the hAM has proved to be an excellent tool for repairing retinal tissue, but it has also shown a promising regeneration potential. This review aims to highlight the novel use of the hAM in treating retinal diseases. Although the hAM has been used in the ocular anterior segment reconstruction for more than 60 years, in the last 2 years, we have found in literature articles showing the use of the hAM in the retinal surgery field with interesting results in terms of tissue healing and photoreceptor regeneration.

Applications of the Amniotic Membrane in Vitreoretinal Surgery

Recently, the use of the human amniotic membrane (hAM) has been extended to treat retinal disorders, such as macular holes that failed to close and retinal tears. The hAM has demonstrated the induction of a recovery process of the external retinal layers involving the external limiting membrane (ELM) and the ellipsoid zone (EZ). After that, the application of the hAM for retinal pathologies was extended to large macular tears, high myopic retinal detachment associated with MH, paravascular tears, serous macular detachment associated with optic pit, complicated retinal detachment and advanced age-related macular degeneration (AMD). The hAM has shown a potential in repairing retinal tissue through a regeneration process. This review aims to highlight the use of the hAM in various vitreo-retinal surgical fields, and to confront it with other cutting-edge surgical techniques used to treat challenging vitreo-retinal pathologies.

Human Amniotic Membrane Plug to Restore Age-Related Macular Degeneration Photoreceptor Damage

PURPOSE

Age-related macular degeneration (AMD) is the leading cause of legal blindness in adults 65 years of age and older. Choroidal neovascularization (CNV) can complicate AMD and lead to severe visual acuity reduction. Despite the several treatments available, if the retinal pigment epithelium is damaged, we have to cope with the impossibility of restoring acceptable visual acuity using only medical treatments.

DESIGN

Prospective, consecutive, interventional study.

PARTICIPANTS

Eleven patients affected by AMD, 6 patients affected by CNV, and 5 patients affected by geographic atrophy.

METHODS

All patients underwent a pars plana vitrectomy with subretinal implantation of human amniotic membrane (hAM) to induce photoreceptor regeneration and partial visual acuity restoration.

MAIN OUTCOME MEASURES

Primary study outcome was visual acuity improvement. Secondary outcomes were multimodal imaging results.

RESULTS

Mean preoperative best-corrected visual acuity (BCVA) was 20/2000 (2 logarithm of the minimum angle of resolution [logMAR]), and all the patients showed a BCVA of counting fingers or less. Mean final BCVA was 20/400 (1.31 logMAR), ranging from 20/2000 to 20/100 (2-0.7 logMAR). OCT angiography was used to measure retinal vascularization in the treated eye compared with the fellow eye. A high correlation between BCVA and deep vascular density was evidenced. Adaptive optics findings, obtained over the retinal area where the highest functionality was observed, were evaluated using microperimetry. The images showed possible photoreceptor presence over the hAM membrane.

CONCLUSIONS

This work supports the feasibility and safety of the hAM to promote partial retinal function restoration 6 months after surgery with visual acuity improvement. The advanced diagnostics help to understand the interaction between the hAM and photoreceptors and suggest that photoreceptor regeneration may occur.

Tissue-Cultured Human Cord Lining Epithelial Cells in Treatment of Persistent Corneal Epithelial Defect

BACKGROUND:

Persistent corneal epithelial defect (PED) is a consequence of many ocular surface disorders. Although many therapies have been suggested, the treatment of this disease have faced a lot of difficulties up to now. The transplatation of cultivated amniotic epithelial cells sheets is the new promised method for PED. Cord lining epithelial cells (CLECs) are epithelial cells of amniotic membrane of umbilical cord, so these cultivated cells sheet may be good for treating PED

AIM:

To evaluate the efficacy of the transplantation of cultivated CLECs sheets in treatment of PED and analyze some influential factors of this therapy.

METHODS:

A prospective interventional case series with transplantation of tissue-cultured human CLECs in 37 PED eyes in Vietnam National Institute of Ophthalmology.

RESULTS:

Thirty four of 37 eyes were healed with the cells transplantation and 22 eyes of them healed within a week postoperatively. There were normal corneal scars and normal corneal epithelial cell (by impression cytology detection) on transplantation site in all 31 successful cases. The other successful eyes were done lamellar keratoplasty (respectively in 1 month, 3 months, 6 months and 27 months postoperatively) to investigate the histopathology of the CLECs transplant site. The histopathological images showed normal corneal scar and there was no appearance of CLECs in transplant site.

CONCLUSION:

tissue-cultured human CLECs transplantation is a quite safe and effective treatment for persistent corneal epithelial defect. The CLECs may help the epithelial healing at early stage but do not exist at transplant site for a long time.

When an Easy Thing Goes Wrong: Foreign Body Induced Granuloma-Associated Scleritis Following Pterygium Surgery

PURPOSE

To report a case of pterygium surgery with conjunctival autograft followed by focal necrotizing scleritis due to foreign body entrapment in the scleral bed.

CASE REPORT/RESULTS

This is a case report of a 76-years-old male patient who underwent nasal pterygium surgery and developed focal necrotizing scleritis secondary to foreign body entrapment under conjunctival autograft. One month following surgery, slit-lamp examination demonstrated a progressive thinning of the surgical area with focal inflammatory signs. A small synthetic fiber was identified to be trapped under the graft. A second intervention was performed with foreign body removal and a new conjunctival graft. Despite the surgery, focal scleral melting continued to progress and the patient was placed under systemic corticotherapy and submitted to amniotic membrane graft with epithelial side up. During the follow-up period there was a good tissue response.

CONCLUSION

Despite being a safe and quick procedure, pterygium surgery can sometimes elicit new challenges.

Culture of Oral Mucosal Epithelial Cells for the Purpose of Treating Limbal Stem Cell Deficiency

The cornea is critical for normal vision as it allows allowing light transmission to the retina. The corneal epithelium is renewed by limbal epithelial cells (LEC), which are located in the periphery of the cornea, the limbus. Damage or disease involving LEC may lead to various clinical presentations of limbal stem cell deficiency (LSCD). Both severe pain and blindness may result. Transplantation of cultured autologous oral mucosal epithelial cell sheet (CAOMECS) represents the first use of a cultured non-limbal autologous cell type to treat this disease. Among non-limbal cell types, CAOMECS and conjunctival epithelial cells are the only laboratory cultured cell sources that have been explored in humans. Thus far, the expression of p63 is the only predictor of clinical outcome following transplantation to correct LSCD. The optimal culture method and substrate for CAOMECS is not established. The present review focuses on cell culture methods, with particular emphasis on substrates. Most culture protocols for CAOMECS used amniotic membrane as a substrate and included the xenogeneic components fetal bovine serum and murine 3T3 fibroblasts. However, it has been demonstrated that tissue-engineered epithelial cell sheet grafts can be successfully fabricated using temperature-responsive culture surfaces and autologous serum. In the studies using different substrates for culture of CAOMECS, the quantitative expression of p63 was generally poorly reported; thus, more research is warranted with quantification of phenotypic data. Further research is required to develop a culture system for CAOMECS that mimics the natural environment of oral/limbal/corneal epithelial cells without the need for undefined foreign materials such as serum and feeder cells.

Electrospun mat with eyelid fat-derived stem cells as a scaffold for ocular epithelial regeneration

The aim of this study was to develop nanofibrous gelatin substrates for eyelid fat stem cell (EFSC) expansion that can serve as a potential alternative substrate to replace human amniotic membrane. Biocompatibility results indicated that all substrates were highly biocompatible, as EFSCs could favorably attach and proliferate on the nanofibrous surfaces. Microscopic figures showed that the EFSC were firmly anchored to the substrates and were able to retain a normal stem cell phenotype. Immunocytochemistry (ICC) and real time-PCR results revealed change in the expression profile of EFSCs grown on nanofibrous substrates when compared to those grown on control in epithelial induction condition. In addition, electrospun gelatin mats especially oriented scaffold provides not only a milieu supporting EFSCs expansion, but also serves as a useful alternative carrier for ocular surface tissue engineering and could be used as an alternative substrate to amniotic membrane.

The Tissue-Engineered Vascular Graft-Past, Present, and Future

Cardiovascular disease is the leading cause of death worldwide, with this trend predicted to continue for the foreseeable future. Common disorders are associated with the stenosis or occlusion of blood vessels. The preferred treatment for the long-term revascularization of occluded vessels is surgery utilizing vascular grafts, such as coronary artery bypass grafting and peripheral artery bypass grafting. Currently, autologous vessels such as the saphenous vein and internal thoracic artery represent the gold standard grafts for small-diameter vessels (<6 mm), outperforming synthetic alternatives. However, these vessels are of limited availability, require invasive harvest, and are often unsuitable for use. To address this, the development of a tissue-engineered vascular graft (TEVG) has been rigorously pursued. This article reviews the current state of the art of TEVGs. The various approaches being explored to generate TEVGs are described, including scaffold-based methods (using synthetic and natural polymers), the use of decellularized natural matrices, and tissue self-assembly processes, with the results of various in vivo studies, including clinical trials, highlighted. A discussion of the key areas for further investigation, including graft cell source, mechanical properties, hemodynamics, integration, and assessment in animal models, is then presented.

Human amniotic epithelial cells suppress relapse of corticosteroid-remitted experimental autoimmune disease

BACKGROUND AIMS

Multiple sclerosis (MS) is considered to be a T-cell-mediated disease. Although MS remits with corticosteroid treatment, the disease relapses on discontinuation of therapy. Human amniotic epithelial cells (hAEC) from the placenta are readily accessible in large quantities and have anti-inflammatory properties. Previously we reported that hAEC given near disease onset ameliorated clinical signs and decreased myelin oligodendrocyte glycoprotein (MOG)-specific immune responses in MOG-induced experimental autoimmune encephalomyelitis (EAE), an experimental MS model.

METHODS

To examine the therapeutic effect of hAEC in a clinically relevant setting, we first treated MOG peptide-induced EAE mice with a corticosteroid, prednisolone, in drinking water to induce remission. hAEC were then infused intravenously into the remitted mice. Anti-MOG antibodies in serum were detected by enzyme-linked immunoassay. Splenocyte proliferation was assessed by (3)H-thymidine incorporation. Immune cell subpopulations in spleens and lymph nodes and secreted cytokines in splenocyte culture were quantified by flow cytometry. Central nervous system histology was examined with the use of hematoxylin and eosin, Luxol fast blue and immunostaining.

RESULTS

With cessation of prednisolone treatment, hAEC delayed EAE relapse for 7 days, and, after another 7 days, largely remitted disease in six of eight responder mice. Splenocyte proliferation was suppressed, anti-MOG35-55 antibodies in serum were decreased and interleukin-2 and interleukin-5 production by splenocytes were elevated after hAEC treatment. In the central nervous system, hAEC-treated mice had decreased demyelination and fewer macrophages in the inflammatory infiltrates. hAEC treatment also increased CD4(+)CD25(+)FoxP3(+) regulatory T cells in inguinal lymph nodes.

CONCLUSIONS

These data demonstrate that the therapeutic effects of hAEC after corticosteroid treatment in an MS model probably are the consequence of peripheral immunoregulation. We suggest that hAEC may have potential as a cell therapy for remitted MS.

A prototype tissue engineered blood vessel using amniotic membrane as scaffold

In this study, we used amniotic membrane (AM), a natural extracellular matrix, as a scaffold for the fabrication of tissue engineered blood vessels (TEBVs). The inner surface of the denuded glutaraldehyde cross-linked AM tube was endothelialized with porcine vascular endothelial cells (ECs) and subjected to a physiological (12 dynecm(-2)) shear stress (SS) for 2 and 4 days. The results showed that after applying SS, an intact EC monolayer was maintained in the lumen surface of the TEBV. The ECs were aligned with their long axis parallel to the blood flow. The immunofluorescent microscopy showed that the intercellular junctional proteins, PECAM-1 and VE-cadherin, were surrounding the EC periphery and were better developed and more abundant in SS-treated TEBVs than the static controls. The Western blot indicated that the expressions of PECAM-1 and VE-cadherin were increased by 72 ± 9% and 67 ± 7%, respectively, after shear stress treatment. The distribution pattern of integrin β1 was mainly at the interface of ECs and AM in static TEBVs but it was extended to the cell-cell junctions after SS treatment. The SS promoted the expression of integrin α(v)β(3) without altering its distribution in TEBV. The results suggest that glutaraldehyde cross-linked AM tube can potentially be used as a scaffold biomaterial for TEBV fabrication. Most importantly, the use of an AM tube shortened the TEBV fabrication.

Regenerative approaches as alternatives to donor allografting for restoration of corneal function

A range of alternatives to human donor tissue for corneal transplantation are being developed to address the shortfall of good quality tissues as well as the clinical conditions for which allografting is contraindicated. Classical keratoprostheses, commonly referred to as artificial corneas, are being used clinically to replace minimal corneal function. However, they are used only as last resorts, as they are associated with significant complications, such as extrusion/rejection, glaucoma, and retinal detachment. The past few years have seen significant developments in technologies designed to replace part or the full thickness of damaged or diseased corneas with materials that encourage regeneration to different extents. This review describes selected examples of these corneal substitutes, which range from cell-based regenerative strategies to keratoprostheses with regenerative capabilities via tissue-engineered scaffolds pre-seeded with stem cells. It is unlikely that one corneal substitute will be best for all indications, but taken together, the various approaches may soon be able to supplement the supply of human donor corneas for transplantation or allow restoration of diseased or damaged corneas that cannot be treated by currently available techniques.

Osteogenic differentiation of intact human amniotic membrane

Tissue engineering strategies usually require cell isolation and combination with a suitable biomaterial. Human amniotic membrane (AM) represents a natural two-layered sheet comprising cells with proven stem cell characteristics. In our approach, we evaluated the differentiation potential of AM in toto with its sessile stem cells as alternative to conventional approaches requiring cell isolation and combination with biomaterials. For this, AM-biopsies were differentiated in vitro using two osteogenic media compared with control medium (CM) for 28 days. Mineralization and osteocalcin expression was demonstrated by (immuno)histochemistry. Alkaline phosphatase (AP) activity, calcium contents and mRNA expression of RUNX2, AP, osteopontin, osteocalcin, BMP-2 (bone morphogenetic protein), and BMP-4 were quantified and AM viability was evaluated. Under osteogenic conditions, AM-biopsies mineralized successfully and by day 28 the majority of cells expressed osteocalcin. This was confirmed by a significant rise in calcium contents (up to 27.4 ± 6.8 mg/dl d28), increased AP activity, and induction of RUNX2, AP, BMP-2 and BMP-4 mRNA expression. Relatively high levels of viability were retained, especially in osteogenic media (up to 78.3 ± 19.0% d14; 62.9 ± 22.3% d28) compared to CM (42.2 ± 15.2% d14; 35.1 ± 8.6% d28). By this strategy, stem cells within human AM can successfully be driven along the osteogenic pathways while residing within their natural environment.

Evaluation of the role of ProKera in the management of ocular surface and orbital disorders

OBJECTIVES

To report the efficacy and safety profile of sutureless and adhesiveless amniotic membrane device (ProKera, Bio-Tissue, Inc., Miami, FL) in the management of various ocular surface and orbital disorders.

METHODS

Twenty eyes of 20 patients underwent placement of 21 ProKera implants between March 2006 and July 2007 at the University of Texas Southwestern Medical Center. Patient demographics, indications for placement, and duration of ProKera retention were recorded. Outcomes measured included corneal epithelial healing, visual acuity, patient tolerance, and adverse events.

RESULTS

ProKera was most commonly used in patients with corneal neovascularization with or without limbal stem-cell deficiency (10 eyes). Other indications included recurrent pterygium or pseudopterygium (three eyes), anophthalmic orbit contraction (two eyes), persistent epithelial defects (two eyes), severe thinning in a corneal ulcer (one eye), benign hereditary intraepithelial dyskeratosis (one eye), and band keratopathy (one eye). The mean duration of ProKera retention was 25.3 days (range, 0-125) visual acuity improved in 12 eyes (60%). Immediate adverse events included residual epithelial defects after removal (five eyes) and spontaneous extrusion of the implant (four eyes). Six patients (30%) reported eye pain or headache and four eyes (20%) had recurrence of the primary pathology.

CONCLUSIONS

Sutureless and adhesiveless amniotic membrane transplantation is a safe and effective method to promote healing and reconstruction of the ocular surface and orbit with minimal side effects. Recurrence of the underlying primary pathology remains a concern. The advent of a newer, softer conformer ring may improve patient tolerability and limit discomfort.

Implantation of amniotic membrane to reduce postlaminectomy epidural adhesions

Postlaminectomy epidural adhesion is implicated as a main cause of "failed back surgery syndrome" and associated with increased risk of complications during revision surgery. Various materials acting as mechanical barriers to reduce fibroblasts infiltration into epidural space have met with limited success. In present research, amniotic membrane (AM) was studied to investigate its effects on reducing epidural scar adhesion after laminectomy in a canine model. Laminectomy sites were created at L-1, L-3, L-5, and L-7 levels in 24 adult mongrel dogs. Freeze dried AM (FAM), cross-linked AM (CAM), and autologous free fat (AFF) were implanted, respectively, at a randomly assigned site in each dog with the remaining untreated site serving as internal control. The animals were sacrificed at 1, 6, and 12 weeks postoperatively. Then, gross pathologic observation including scar amount and adhesion tenacity, qualitative histology evaluation, and quantitative histology analysis were compared. Gross observation demonstrated that scar amount and adhesion tenacity of CAM group were significantly lower in comparison with those of FAM and non-treatment groups. A white, slightly vascularized CAM layer covered the dura mater without tenacious scar adhesion. The histology analysis also indicated reduced fibroblasts infiltration and consequent epidural fibrosis, which were similar to the results of AFF group. In conclusion, the CAM is effective in reducing epidural fibrosis and scar adhesion after laminectomy in canine model. It is a promising biomaterial for future clinical applications.

The influence of various storage conditions on cell viability in amniotic membrane

Up to now freeze-dried, gamma-sterilised or glycerol-preserved amniotic membranes (AMs) have widely been used in the field of ophthalmology and wound care (e.g. leg ulcers, burns). After some preservation processes in use, like freeze-drying or glycerol-preserving, the cells in the AM are no longer viable. Within this study we evaluated the influence of different short-term and long-term storage conditions on cell viability in AM. Therefore AMs from cesarean section placentae were washed and biopsied to evaluate the microbiological status and to determine the viability of the tissue. Additionally, viability under various storage conditions was examined by assessment of mitochondrial activity. Preservation included temperatures above and below 0 degrees C as well as various media compositions. As expected, cell viability in amnion decreases during storage, in fact the effect was more pronounced when stored frozen, but the higher viability of amnion obtained by storage above 0 degrees C with medium is associated with the limitation to a short period of storage of about 28 days. The evaluated preservation methods are the basis for future non-clinical in-vivo studies in which the possible benefit of amnion as a viable biomaterial in wound healing will be investigated.

The effect of amniotic membrane preparation method on its ability to serve as a substrate for the ex-vivo expansion of limbal epithelial cells

Human amniotic membrane (HAM) is employed as a substrate for the ex-vivo expansion of limbal epithelial cells (LECs) used to treat corneal epithelial stem cell deficiency in humans. The optimal method of HAM preparation for this purpose is unknown. This study evaluated the ability of different preparations of stored HAM to serve as substrates for LEC expansion ex-vivo. The effect of removing the amniotic epithelial cells (decellularisation) from HAM prior to seeding of LECs, the effect of glycerol cryopreservation and the effect of peracetic acid (PAA) sterilization and antibiotic disinfection were evaluated using different HAM test groups. Human LECs were cultured on each preparation and the following outcomes were assessed: confluence of growth, cell density, cell morphology and expression of the putative LESC markers deltaN-p63alpha and ABCG2. Removing amniotic epithelial cells prior to seeding of LECs resulted in a higher percentage of confluence but a lower cell density than intact HAM suggesting that decellularisation does not increase proliferation, but rather that it facilitates migration of LECs resulting in larger cells. Decellularisation did not affect the percentage of cells expressing the putative LESC markers deltaN-p63alpha (< or =4% in both intact and acellular groups) and ABCG2 (< or =3% in both intact and acellular groups). Glycerol cryopreservation of HAM resulted in poor morphology and a low proportion of cells expressing deltaN-p63alpha (< or =6%) and ABCG2 (< or =8%). HAM frozen at -80 degrees C in Hank's Balanced Salt Solution (HBSS) was superior, demonstrating excellent morphology of cultured LECs and high levels of deltaN-p63alpha (< or =68%) and ABCG2 (< or =62%) expression (p<0.001). The use of PAA or antibiotics to decontaminate HAM does not appear to affect this function. The variables affecting the ability of HAM to serve as a substrate for LEC expansion ex-vivo are poorly understood. The use of glycerol as a cryoprotectant impairs this ability whereas simple frozen HAM appears to work extremely well for this purpose.

Concise review: isolation and characterization of cells from human term placenta: outcome of the first international Workshop on Placenta Derived Stem Cells

Placental tissue draws great interest as a source of cells for regenerative medicine because of the phenotypic plasticity of many of the cell types isolated from this tissue. Furthermore, placenta, which is involved in maintaining fetal tolerance, contains cells that display immunomodulatory properties. These two features could prove useful for future cell therapy-based clinical applications. Placental tissue is readily available and easily procured without invasive procedures, and its use does not elicit ethical debate. Numerous reports describing stem cells from different parts of the placenta, using nearly as numerous isolation and characterization procedures, have been published. Considering the complexity of the placenta, an urgent need exists to define, as clearly as possible, the region of origin and methods of isolation of cells derived from this tissue. On March 23-24, 2007, the first international Workshop on Placenta Derived Stem Cells was held in Brescia, Italy. Most of the research published in this area focuses on mesenchymal stromal cells isolated from various parts of the placenta or epithelial cells isolated from amniotic membrane. The aim of this review is to summarize and provide the state of the art of research in this field, addressing aspects such as cell isolation protocols and characteristics of these cells, as well as providing preliminary indications of the possibilities for use of these cells in future clinical applications.

Dose-dependent immunomodulatory effect of human stem cells from amniotic membrane: a comparison with human mesenchymal stem cells from adipose tissue

Bone marrow-derived mesenchymal stem cells (BMSCs) have been used for allogeneic application in tissue engineering but have certain drawbacks. Therefore, stem cells (SC)s derived from other adult tissue sources have been considered as an alternative. However, there is only limited knowledge on their immunomodulatory properties. The aim of our study was to compare the immunomodulatory potential of human amniotic mesenchymal and human amniotic epithelial cells with that of human adipose-derived SCs under identical experimental conditions. We have demonstrated a dose-dependent inhibition of peripheral blood mononuclear cell (PBMC) immune responses in mixed lymphocyte reactions (up to 66-93% inhibition) and phytohemagglutinin activation assays (up to 67-96% inhibition). The lowest SC-to-PBMC ratio able to inhibit PBMC proliferation significantly was 1:8. Subcultivation (passage 2-6) did not alter immunoinhibitory properties, whereas cryopreservation significantly reduced the immunomodulatory potential. Using transwell systems, we have demonstrated an inhibition mechanism that is dependent on cell contact. Additionally, in coculture with allogeneic PBMCs, SCs were well tolerated and at most provoked mild alloreactions in singular cases. This study demonstrates, for the first time, contact- and dose-dependent immunosuppression of mesenchymal and epithelial amniotic SC populations, as well as of adipose tissue-derived SCs. All three cell types may be considered as possible alternatives to BMSCs for allogeneic application in tissue engineering.

Isolation, characterization, and differentiation of stem cells derived from the rat amniotic membrane

Stem-cell-based therapies may offer treatments for a variety of intractable diseases. A fundamental goal in stem-cell biology concerns the characterization of diverse populations that exhibit different potentials, growth capabilities, and therapeutic utilities. We report the characterization of a stem-cell population isolated from tissue explants of rat amniotic membrane. Similar to mesenchymal stem cells, these amnion-derived stem cells (ADSCs) express the surface markers CD29 and CD90, but were negative for the lymphohematopoietic markers CD45 and CD11b. ADSCs exist in culture in a multidifferentiated state, expressing neuroectodermal (neurofilament-M), mesodermal (fibronectin), and endodermal (alpha-1-antitrypsin) genes. To assess plasticity, ADSCs were subjected to a number of culture conditions intended to encourage differentiation into neuroectodermal, mesodermal, and endodermal cell types. ADSCs cultured in a defined neural induction media assumed neuronal morphologies and up-regulated neural-specific genes. Under different conditions, ADSCs were capable of differentiating into presumptive bone and fat cells, indicated by the deposition of mineralized matrix and accumulated lipid droplets, respectively. Moreover, ADSCs cultured in media that promotes liver cell differentiation up-regulated liver-specific genes (albumin) and internalized low-density lipoprotein (LDL), consistent with a hepatocyte phenotype. To determine whether this observed plasticity reflects the presence of true stem cells within the population, we have derived individual clones from single cells. Clonal lines recapitulate the expression pattern of parental ADSC cultures and are multipotent. ADSCs have been cultured for 20 passages without losing their plasticity, suggesting long-term self-renewal. In sum, our data suggest that ADSCs and derived clonal lines are capable of long-term self-renewal and multidifferentiation, fulfilling all the criteria of a stem-cell population.

Characterization of porcine arterial endothelial cells cultured on amniotic membrane, a potential matrix for vascular tissue engineering

The existing of basement membrane improves the development of endothelium while constructing blood vessel equivalent. The amniotic membrane (AM) provides a natural basement membrane and has been used in ocular surface reconstruction. This study evaluated the molecular and cellular characteristics of porcine vascular endothelial cells (ECs) cultured on AM. ECs cultured on AM expressed the endothelial marker vWF and exhibited normal endothelial morphology. Here, we demonstrated that AM enhanced the expression of intercellular molecules, platelet-endothelial cell adhesion molecule-1 (PECAM-1), and adhesion molecule VE-cadherin at the intercellular junctions. The expression level of integrin was markedly higher in ECs cultured on AM than on plastic dish. Furthermore, the AM downregulated the expression of E-selectin and P-selectin in both LPS-activated and non-activated ECs. Consistently, adhesion of leukocytes to both activated and non-activated cells was decreased in ECs cultured on AM. Our results suggest that AM is an ideal matrix to develop a functional endothelium in blood vessel equivalent construction.

Cultured human ocular surface epithelium on therapeutic contact lenses

BACKGROUND

This study was initiated after observation of some intriguing epithelial growth properties of contact lenses used as a bandage for patients after pterygium surgery.

AIM

To determine the efficacy of culturing human ocular surface epithelial cells on therapeutic contact lenses in autologous serum with a view of using this system to transfer epithelial cells to patients with persistent corneal or limbal defects.

METHODS

Excess graft tissue resected from patients undergoing pterygium surgery (n = 3) consisting of limbal epithelium was placed on siloxane-hydrogel contact lenses (lotrafilcon A and balafilcon A). Limbal explants were cultured in media with 10% autologous serum. Morphology, proliferative capacity and cytokeratin profile were determined by phase contrast, light and electron microscopy, and immunohistochemical analysis.

RESULTS

Lotrafilcon A contact lenses sustained proliferation and migration from limbal tissue. Cells became confluent after 10-14 days and consisted of 2-3 layers with a corneal phenotype (CK3(+)/CK12(+)/CK19(-)) and a propensity to proliferate (p63(+)). Electron microscopy showed microvilli on the apical surface with adhesive projections, indicating that these cells were stable and likely to survive for a long term. Growth was not observed from limbal explants cultured on balafilcon A contact lenses.

CONCLUSION

A method for culturing human ocular surface epithelium on contact lenses that may facilitate expansion and transfer of autologous limbal epithelial cells while avoiding the risks associated with transplanting allogeneic tissue has been developed. This technique may be potentially useful for the treatment of patients with limbal stem cell deficiency.

Ocular surface restoration using non-surgical transplantation of tissue-cultured human amniotic epithelial cells

PURPOSE

To assess the effect of tissue-cultured human amniotic epithelial cells (AECs) in restoring the ocular surface, transplanted using a collagen shield seeded with AECs supported by a soft contact lens.

DESIGN

Prospective interventional single-institutional case series with crossover controls.

METHODS

Three eyes in three patients were identified with persistent corneal epithelial defects (PEDs) refractory to medical therapy. Two cases were secondary to neurotrophic keratopathy, while one case was attributable to longstanding alkali injury. AECs were isolated from serologically screened donor human placenta, seeded onto collagen corneal shields, and incubated in tissue culture medium for 7 days. These collagen shields were placed over the PED and supported by an overlying soft contact lens. The collagen shields dissolved by 72 hours, and the contact lenses were removed after this time. This cycle was repeated every week until healing was achieved. As a crossover control, collagen shields without AECs were placed in the same eye 1 week before placing collagen shields containing AECs. The PED was assessed by vital staining and slit-lamp color photography.

RESULTS

The PEDs had a mean duration of 4 months and involved 20% to 37% of the corneal surface area, one case secondary to longstanding alkali injury and two cases attributable to neurotrophic keratopathy. No change in PED size was observed in those control eyes receiving collagen shields without AECs. Complete resolution of the PED was seen after two cycles of AEC-seeded collagen shield in one case, and four cycles in two cases, from 7 to 12 weeks following treatment in all patients. No loss of visual acuity was seen and clinical improvement was maintained in all cases, with a mean follow-up of 6.3 months.

CONCLUSIONS

Nonsurgical transplantation of tissue-cultured AECs on a collagen shield provides a promising approach to restoring the ocular surface in cases of PED.