Long-term viability of cryopreserved cultured epithelial grafts

Comparing the Effects of Two Cryoprotectant Protocols, Dimethyl-Sulfoxide (DMSO) and Glycerol, on the Recovery Rate of Cultured Keratinocytes on Amniotic Membrane

Background: Off-the-shelf supply of viable engineered tissue is critical for effective and fast treatment of life-threatening injuries such as deep burns. An expanded keratinocyte sheet on the human amniotic membrane (KC sheet-HAM) is a beneficial tissue-engineering product for wound healing. To access an on-hand supply for the widespread application and overcome the time-consuming process, it is necessary to develop a cryopreservation protocol that guarantees the higher recovery of viable keratinocyte sheets after freeze-thawing. This research aimed to compare the recovery rate of KC sheet-HAM after cryopreservation by dimethyl-sulfoxide (DMSO) and glycerol. Methods: Amniotic membrane was decellularized with trypsin, and keratinocytes were cultured on it to form a multilayer, flexible, easy-to-handle KC sheet-HAM. The effects of 2 different cryoprotectants were investigated by histological analysis, live-dead staining, and proliferative capacity assessments before and after cryopreservation. Results: KCs well adhered and proliferated on the decellularized amniotic membrane and successfully represented 3 to 4 stratified layers of epithelialization after 2 to 3 weeks culture period; making it easy to cut, transfer, and cryopreserve. However, viability and proliferation assay indicated that both DMSO and glycerol cryosolutions have detrimental effects on KCs, and KCs-sheet HAM could not recover to the control level after 8 days of culture post-cryo. The KC sheet lost its stratified multilayer nature on AM, and sheet layers were reduced in both cryo-groups compared to the control. Conclusion: Expanding keratinocytes on the decellularized amniotic membrane as a multilayer sheet made a viable easy-to-handle sheet, nonetheless cryopreservation reduced viability and affected histological structure after thawing. Although some viable cells were detectable, our research highlighted the need for a better cryoprotectant protocol other than DMSO and glycerol, specific for the successful banking of viable tissue constructs.

Recent Advances in Cell Sheet Engineering: From Fabrication to Clinical Translation

Cell sheet engineering, a scaffold-free tissue fabrication technique, has proven to be an important breakthrough technology in regenerative medicine. Over the past two decades, the field has developed rapidly in terms of investigating fabrication techniques and multipurpose applications in regenerative medicine and biological research. This review highlights the most important achievements in cell sheet engineering to date. We first discuss cell sheet harvesting systems, which have been introduced in temperature-responsive surfaces and other systems to overcome the limitations of conventional cell harvesting methods. In addition, we describe several techniques of cell sheet transfer for preclinical (in vitro and in vivo) and clinical trials. This review also covers cell sheet cryopreservation, which allows short- and long-term storage of cells. Subsequently, we discuss the cell sheet properties of angiogenic cytokines and vasculogenesis. Finally, we discuss updates to various applications, from biological research to clinical translation. We believe that the present review, which shows and compares fundamental technologies and recent advances in cell engineering, can potentially be helpful for new and experienced researchers to promote the further development of tissue engineering in different applications.

An Anhydrous Sodium Chloride Skin Preservation Model for Studies on Keratinocytes Grafting into the Wounds

Background. Human skin is needed for covering large body areas lost by trauma. The shortcomings of contemporary methods of skin storage are limited preservation time and high immunogenicity if allogeneic. Methods. We investigated whether long-lasting skin preservation in anhydrous sodium chloride (NaCl) may be the source of keratinocytes (KCs) for transplantation. Dehydrated skin fragments were preserved for a time frame from 1 week to 12 months. Then, skin fragments were rehydrated, and KCs were isolated. The viability of KCs was assessed in viability/cytotoxicity test. NaCl-preserved KCs were cultured for 7 days and transplanted to the dorsum of SCID mice. Results. The morphology of NaCl-preserved KCs was unaltered. KCs from all epidermal layers could be identified. All grafts were accepted by the recipients. Transplanted KCs: synthesized keratins 10 and 16 expressed antigens specific for stem cells and transient-amplifying cells, and remained HLA-I-positive. Moreover, they expressed the proliferative marker PCNA. Cells isolated from transplants remained viable and produced enzymes. Conclusions. Transplantation of KCs obtained from human skin and stored in anhydrous NaCl may be considered for the closure of extensive skin wounds. The originality of this method consists of an effective storage procedure and easy preparation of keratinocytes for transplantation.

Cryopreserved cultured epithelial allografts for pediatric deep partial dermal burns: Early wound closure and suppression of scarring

BACKGROUND

In deep partial thickness dermal burns (DDB) where greater than 50% of the dermis is lost, severe pain, scarring and contractures occur. Therefore, skin grafting may be required. In children, scar contracture occurs because scarred skin does not stretch with growth creating the need for additional scar-releasing or skin-grafting surgeries. In order to resolve this problem, we used cryopreserved cultured epithelial allograft (cryopreserved allo-CEG), which can be grafted shortly after sustaining a wound. We reevaluated the promotion of early wound closure of burns and suppression of scarring by this treatment.

METHODS

Cryopreserved allo-CEGs were used to treat 50 cases of pediatric DDB from 1992 to 2000. These cases were reviewed with regard to the time until epithelialization, take percentage, and pain level. Also, in order to examine why cryopreserved allo-CEG promotes healing of burns and suppresses scarring, growth factors and cytokines in the cryopreserved allo-CEG were measured. Cryopreserved allo-CEG sheets were solubilized and concentrations of TGF-α, TGF-β1, IL-1α, IL-1β, PDGF-AA, VEGF, KGF, IL-6, b-FGF, as well as metalloprotease-1 (MMP-1) and HGF, which are noted to have scarring suppression effects, were measured before grafting.

RESULTS

Grafting of cryopreserved allo-CEGs in 50 cases of childhood DDB resulted in early epithelialization (9.32 ± 3.63 days on the average) and an almost 100% take rate. Also, pain relief (pain reduction or elimination, reduced need for anesthetics) was seen in all cases. Although 15-23 years have now elapsed, adverse events have not been observed. Cryopreserved allo-CEG contains IL-1α, IL-1β, PDGF-AA, TGF-α, TGF-β1, VEGF, and IL-6 have wound healing effects. The concentration of IL-1α was higher than the concentrations of other components, and this was followed by TGF-α, TGF-β1, b-FGF and VEGF. Although the concentration of MMP-1, which has a scarring suppression effect, was high, HGF was not detected.

CONCLUSION

Cryopreserved allo-CEG contains growth factors that promote wound healing and factors that suppress scarring. Three effects, namely (1) early wound closure, (2) scarring suppression, and (3) pain relief were seen with grafts of cryopreserved allo-CEG in cases of childhood DDB. These observations show that cryopreserved allo-CEG is clinically useful and effective for the treatment of childhood DDB.

Assessment of cryopreserved donor skin viability: the experience of the regional tissue bank of Siena

Skin allografts from cadaver donors are an important resource for treating extensive burns, slow-healing wounds and chronic ulcers. A high level of cell viability of cryopreserved allografts is often required, especially in burn surgery, in Italy. Thus, we aimed to determine which conditions enable procurement of highly viable skin in our Regional Skin Bank of Siena. For this purpose, we assessed cell viability of cryopreserved skin allografts procured between 2011 and 2013 from 127 consecutive skin donors, before and after freezing (at day 15, 180, and 365). For each skin donor, we collected data concerning clinical history (age, sex, smoking, phototype, dyslipidemia, diabetes, cause of death), donation process (multi-tissue or multi-organ) and timing of skin procurement (assessment of intervals such as death-harvesting, harvesting-banking, death-banking). All these variables were analysed in the whole case study (127 donors) and in different groups (e.g. multi-organ donors, non refrigerated multi-tissue donors, refrigerated multi-tissue donors) for correlations with cell viability. Our results indicated that cryopreserved skin allografts with higher cell viability were obtained from female, non smoker, heartbeating donors died of cerebral haemorrhage, and were harvested within 2 h of aortic clamping and banked within 12 h of harvesting (13-14 h from clamping). Age, cause of death and dyslipidaemia or diabetes did not appear to influence cell viability. To maintain acceptable cell viability, our skin bank needs to reduce the time interval between harvesting and banking, especially for refrigerated donors.

An evaluation of the choice of feeder cell growth arrest for the production of cultured epidermis

Growth arrested 3T3 cells have been used as feeder cells in human epidermal keratinocyte cultures to produce cultured epidermal autografts for the treatment of burns. The feeder cells were ideally growth-arrested by gamma-irradiation. Alternatively, growth arrest by mitomycin C treatment is a cost effective option. We compared the functional efficacy of these two approaches in keratinocyte cultures by colony forming efficiency, the net growth area of colonies, BrdU labeling and histological features of cultured epidermal sheets. The growth area estimation involved a semi-automated digital technique using the Adobe Photoshop and comprised of isolation and enumeration of red pixels in Rhodamine B-stained keratinocyte colonies. A further refinement of the technique led to the identification of critical steps to increasing the degree of accuracy and enabling its application as an extension of colony formation assay. The results on feeder cell functionality revealed that the gamma irradiated feeders influenced significantly higher colony forming efficiency and larger growth area than the mitomycin C treated feeders. The BrdU labeling study indicated significant stimulation of the overall keratinocyte proliferation by the gamma irradiated feeders. The cultured epidermal sheets produced by gamma feeders were relatively thicker than those produced by mitomycin C feeders. We discussed the clinical utility of mitomycin C feeders from the viewpoint of cost-effective burn care in developing countries.

Effect of Storage Temperature on the Phenotype of Cultured Epidermal Cells Stored in Xenobiotic-Free Medium

PURPOSE

Cultured epidermal cell sheets (CECS) are used in the treatment of large area burns to the body and have potential to treat limbal stem cell deficiency (LSCD) as shown in animal studies. Despite widespread use, storage options for CECS are limited. Short-term storage allows flexibility in scheduling surgery, quality control and improved transportation to clinics worldwide. Recent evidence points to the phenotype of cultured epithelial cells as a critical predictor of post-operative success following transplantation of CECS in burns and in transplantation of cultured epithelial cells in patients with LSCD. This study, therefore assessed the effect of a range of temperatures, spanning 4-37 °C, on the phenotype of CECS stored over a 2-week period in a xenobiotic-free system.

MATERIALS AND METHODS

Progenitor cell (p63, ΔNp63α and ABCG2) and differentiation (C/EBPδ and CK10) associated marker expression was assessed using immunocytochemistry. Immunohistochemistry staining of normal skin for the markers p63, ABCG2 and C/EBPδ was also carried out. Assessment of progenitor cell side population (SP) was performed using JC1 dye by flow cytometry.

RESULTS

P63 expression remained relatively constant throughout the temperature range but was significantly lower compared to control between 20 and 28 °C (p < 0.05). High C/EBPδ together with low p63 suggested more differentiation beginning at 20 °C and above. Lower CK10 and C/EBPδ expression most similar to control was seen at 12 °C. The percentage of ABCG2 positive cells was most similar to control between 8 and 24 °C. Between 4 and 24 °C, the SP fluctuated, but was not significantly different compared to control. Results were supported by staining patterns indicating differentiation status associated with markers in normal skin sections.

CONCLUSIONS

Lower storage temperatures, and in particular 12 °C, merit further investigation as optimal storage temperature for maintenance of undifferentiated phenotype in CECS.

Effect of storage temperature on cultured epidermal cell sheets stored in xenobiotic-free medium

Cultured epidermal cell sheets (CECS) are used in regenerative medicine in patients with burns, and have potential to treat limbal stem cell deficiency (LSCD), as demonstrated in animal models. Despite widespread use, short-term storage options for CECS are limited. Advantages of storage include: flexibility in scheduling surgery, reserve sheets for repeat operations, more opportunity for quality control, and improved transportation to allow wider distribution. Studies on storage of CECS have thus far focused on cryopreservation, whereas refrigeration is a convenient method commonly used for whole skin graft storage in burns clinics. It has been shown that preservation of viable cells using these methods is variable. This study evaluated the effect of different temperatures spanning 4°C to 37°C, on the cell viability, morphology, proliferation and metabolic status of CECS stored over a two week period in a xenobiotic–free system. Compared to non-stored control, best cell viability was obtained at 24°C (95.2±9.9%); reduced cell viability, at approximately 60%, was demonstrated at several of the temperatures (12°C, 28°C, 32°C and 37°C). Metabolic activity was significantly higher between 24°C and 37°C, where glucose, lactate, lactate/glucose ratios, and oxygen tension indicated increased activation of the glycolytic pathway under aerobic conditions. Preservation of morphology as shown by phase contrast and scanning electron micrographs was best at 12°C and 16°C. PCNA immunocytochemistry indicated that only 12°C and 20°C allowed maintenance of proliferative function at a similar level to non-stored control. In conclusion, results indicate that 12°C and 24°C merit further investigation as the prospective optimum temperature for short-term storage of cultured epidermal cell sheets.

Cryopreservation of tissue-engineered epithelial sheets in trehalose

Tissue-engineered epidermal membranes are useful for clinical wound healing. To facilitate these products in the clinic, optimized storage methods need to be developed. We studied the efficiency of extracellular trehalose at various concentrations for cryopreserving human tissue-engineered epidermal membranes compared with that of dimethyl-sulfoxide (DMSO) used by most organ banks for cryopreserving skin grafts and artificial skin substitutes. Keratinocyte (KC) viability, proliferation and marker expression following cryopreservation in trehalose were examined with similar results to those using DMSO. Trehalose concentration (0.4m) was optimized according to the described cellular activities following cryopreservation. Artificial epidermal substitutes were then cryopreserved in trehalose at the optimized concentration. Cell viability, growth factor secretion and wound healing properties of cryopreserved artificial epidermal substitutes using nude mice were examined and compared with those of DMSO cryopreservation. Cryopreservation with trehalose enhanced human KC viability in suspension and artificial skin substitutes. In addition, trehalose cryopreservation provided fast recovery of EGF and TGF-β1 secretion by KCs after thawing. When transplanted into nude mice, trehalose-cryopreserved artificial skin repaired skin defects in a similar manner to that of a non-cryopreserved control. Moreover, trehalose-cryopreserved artificial skin resulted in engraftment and wound closure that was significantly enhanced compared with that of DMSO-cryopreserved epidermal membranes. The results indicate that the use of trehalose improves cryopreservation of tissue-engineered epithelial sheets.

The possibility of long-term cryopreservation of cultured dermal substitute

Allogeneic cultured dermal substitute (CDS) was prepared by cultivating fibroblasts on a two-layered spongy matrix of hyaluronic acid (HA) and atelo-collagen (Col). CDS can be cryopreserved and transported to other hospitals in a frozen state. To evaluate cell viability, cell growth, and release of VEGF after long-term cryopreservation, the CDS was cryopreserved at -85 degrees C or -152 degrees C for a given period. We measured cell viability immediately after thawing and cell growth in CDS that was recultured for 1 week after thawing. In addition, the amount of vascular endothelial growth factor (VEGF) released from CDS that was recultured for 1 week after thawing was measured. The cell viability and cell growth of control CDS that was thawed within 3 weeks after freezing was 56.2% and 132.7%, respectively. The cell viability and cell growth of the CDS that was cryopreserved at -85 degrees C for 6 months was 43.4% and 119.7%, respectively. When cryopreserved at -152 degrees C for 1 year, the cell viability and cell growth was 52.0% and 110.8%, respectively. These values were comparable to those of the control. The amount of VEGF released from CDS cryopreserved at -85 degrees C for 6 months (491.0 pg/mL) or at -152 degrees C for 1 year (586.8 pg/mL) was comparable to that of the control CDS (587.3 pg/mL). In contrast, the amounts of VEGF released from CDS cryopreserved at -85 degrees C for 1 year (322.5 pg/mL) or at -152 degrees C for 2 years (210.8 pg/mL) were low, with a marked decrease in cell viability and cell growth. These findings suggest that CDS cryopreserved at -85 degrees C for 6 months or at -152 degrees C for 1 year maintains sufficient cell viability and the ability to proliferate and release a significant amount of VEGF. The release of VEGF from CDS after long-term cryopreservation is a useful therapeutic effect, and is important for clinical use.

Cryopreserved cultured epidermal allografts achieved early closure of wounds and reduced scar formation in deep partial-thickness burn wounds (DDB) and split-thickness skin donor sites of pediatric patients

Burn treatment in children is associated with several difficulties, e.g. available skin replacement is small, donor area could expand, and subsequent hypertrophic scar and contracture could become larger along with their physical growth. In order to have better clinical results, the authors prepared cryopreserved cultured epidermal allografts from excess epidermal cells of other patients, and applied the epidermal allografts to 55 children, i.e. 43 cases of deep partial-thickness burn wounds (DDB) due to scald burn and 12 cases with split-thickness skin donor sites. In the 43 DDB patients, epithelialization was confirmed 9.1+/-3.6 days (mean+/-S.D.) after treatment. In 10 of the 43 patients, epithelialization was comparable between the area which received the epidermal allografts (grafted area) and the area which did not receive the epidermal allografts but was covered with usual wound dressing (non-grafted area). As a result, epithelialization day was 7.9+/-1.7 in grafted areas and 20.5+/-2.3 in non-grafted areas. In the 12 patients with split-thickness skin donor sites, epithelialization was confirmed 6.3+/-0.9 days after treatment. Epithelialization of the grafted and non-grafted areas was comparable in 8 of the 12 patients, and it was 6.5+/-1.1 days and 14.1+/-1.6 days, respectively. In these 10 DDB patients and 8 split-thickness skin donor site patients, redness and scar formation were also milder in the grafted area. The 55 patients have been followed up for 1-8 years (mean, 4.75 years), and scar formation was suppressed in both DDB and split-thickness skin donor sites. These findings showed that cryopreserved cultured epidermal allografts achieve early closure of the wounds and good functional outcomes.