Screening pigs for xenotransplantation: expression of porcine endogenous retroviruses in transgenic pig skin

The clinical outcomes of xenografts in the treatment of burn patients: a systematic review and meta-analysis

BACKGROUND

Although autografts are not feasible in patients with extensive burn wounds, allografts and xenografts can be used for temporary coverage. In this systematic review and meta-analysis, we compared the outcomes of xenografts and the standard treatment of burn wounds.

METHODS

International online databases were searched for English articles comparing xenografts with routine treatment in the burn patients. The random-effects model was used to estimate standardized mean differences (SMD) or odds ratios (OR) with a 95% confidence interval (CI).

RESULTS

From a total of 7144 records, 14 studies were included in our review after screening by title and abstracts followed by full-texts. No significant difference in hospital stays was found between the mammalian xenografts and control groups (SMD [95% CI] = - 0.18 [- 0.54-0.18]). The mean number of dressing changes was significantly lower in both mammalian xenografts compared to the controls (SMD [95% CI] = - 1.01 [- 1.61-- 0.41]) and fish xenografts compared to controls (SMD [95% CI] = - 6.16 [- 7.65-- 4.66]). In the fish xenografts, re-epithelialization time was significantly lower compared to controls (SMD [95% CI] = - 1.18 [- 2.23-- 0.14]).

CONCLUSIONS

Xenografts showed a significantly lower number of dressing changes and fish xenografts showed significant benefit in re-epithelialization compared to routine treatment. The beneficial results of xenografts suggest further research in the use of different types of xenografts in patients with extensive burn.

Current approaches for the regeneration and reconstruction of ocular surface in dry eye

Significant research revealed the preocular tear film composition and regulations that remain vital for maintaining Ocular surface functional integrity. Inflammation triggered by many factors is the hallmark of Ocular surface disorders or dry eyes syndrome (DES). The tear deficiencies may lead to ocular surface desiccation, corneal ulceration and/or perforation, higher rates of infectious disease, and the risk of severe visual impairment and blindness. Clinical management remains largely supportive, palliative, and frequent, lifelong use of different lubricating agents. However, few advancements such as punctal plugs, non-steroidal anti-inflammatory drugs, and salivary gland autografts are of limited use. Cell-based therapies, tissue engineering, and regenerative medicine, have recently evolved as long-term cures for many diseases, including ophthalmic diseases. The present article focuses on the different regenerative medicine and reconstruction/bioengineered lacrimal gland formation strategies reported so far, along with their limiting factors and feasibility as an effective cure in future.

Porcine Endogenous Retroviruses: Quantification of the Viral Copy Number for the Four Miniature Pig Breeds in China

Domestic pigs has served not only as one of the most important economy livestock but also as ideal organ-source animals owing to similarity in anatomy, physiology, and organ size to humans. Howerer, the barrier of the cross-species transmission risk of porcine endogenous retrovirus (PERVs) blocked the pig-to-human xenotransplantation. PERVs are integrated into pigs’ genomes and cannot be eliminated by designated or specified pathogen-free breeding. PERVs are an important biosafety issue in xenotransplantation because they can be released from normal pig cells and infect human cells in vitro under certain conditions. Screening and analyzing the presence of PERVs in pig genome will provide essential parameters for pig breed sources. In China, four miniature pig breeds, such as Guizhou miniature pig (GZ), Bama miniature pig (BM), Wuzhishan miniature pig (WZS), and Juema miniature pig (JM), were the main experimental miniature pig breeds, which were widely used. In this study, PCR was performed to amplify env-A, env-B, and env-C for all individuals from the four breeds. The results revealed that PERV env-A and env-B were detected in all individuals and the lowest ratios of PERV env-C was 17.6% (3/17) in the GZ breed. Then, PERV pol and GAPDH were detected using the droplet digital PCR (ddPCR) method. As the reference of GAPDH copy number, the copy numbers of PERVs were at the median of 12, 16, 14, and 16 in the four miniature pig breeds (GZ, BM, WZS, and JM), respectively. Furthermore, the copy number of the PERV pol gene in many organs from the GZ breed was analyzed using ddPCR. The copy numbers of PERV pol gene were at the median of 7 copies, 8 copies, 8 copies, 11 copies, 5 copies, 6 copies, and 7 copies in heart, liver, spleen, lung, kidney, muscle, and skin, and the maximum number was 11 copies in the lung. The minimum number was 5 copies in the kidney as the reference of GAPDH. These data suggest that GZ breed has the lower PERVs copy number in the genome, and may be an ideal organ-source miniature pig breed for the study of the pig-to-human xenotransplantation.

Porcine Transgenic, Acellular Material as an Alternative for Human Skin

Although new therapeutic approaches for burn treatment have made progress, there is still need for efficient coverage of donor fields. Promising dressing for skin graft donor site should be biocompatible, attach easily to the wound bed, remain in place until donor site has renewed, and decrease morbidity at the site. Porcine skin may be applied as a dressing for severe burns. Therefore pig skin xenografts can be used also as donor field coverage. In the Burn Treatment Centre, we used gauze soaked in Vaseline to secure donor fields. The aim of the study was to check if transgenic porcine skin is better than standard in donor site coverage used in our center. We showed that dressing reduces pain experienced by patients. The dressing leads to a reduction of hospitalization time by an average of 8 days. The dressing is as safe as the gold standard. Securing the donor field reduces the risk of colonization of the wound in the second smear after application by 60%. The disadvantage of the dressing is the inability to absorb blood; the use of hemostatic ointments in combination with the skin of transgenic pigs should be considered in the future.

Is Transgenic Porcine Skin as Good as Allogeneic Skin for Regenerative Medicine? Comparison of Chosen Properties of Xeno- and Allogeneic Material

BACKGROUND

Burn treatment is associated with the need of dressing large cutaneous defects. There is a need of alternative search for the allogeneic skin as a source of grafting for a clinical use. Such sources include animals. For many years, porcine skin was used as a biological dressing for wounds or donor's fields, or residual fields after skin grafting. Current studies aim to minimize immunogenicity, inter alia, through the decellularization process.

MATERIALS AND METHODS

The decellularization methods and porcine skin resettlement of human keratinocytes and fibroblasts were evaluated. The mechanical properties of the dressings and their influence on the viability, apoptosis, population doubling, and cell cycle of keratinocytes and fibroblasts were examined. The inheritance of cell antigens responsible for histocompatibility on the human keratinocyte and fibroblast surface in the cultures incubated with examined variants of dressings from porcine skin were analyzed.

RESULTS

The most effective acellularization method is trypsinization. Morphology of the cell remained proper and stable during the whole experiment. In both fibroblast and keratinocyte cultures, the highest number of apoptotic cells was observed when samples were incubated with allogeneic skin. In the keratinocyte cultures, the highest number of live cells was observed when incubated with porcine transgenic acellular dermal matrix. The acellular matrices influence the increase of population doubling of keratinocytes in the cultures.

CONCLUSION

For routine acellurization, trypsinization was chosen as the most effective method with preservation of tissue properties.

Skin xenotransplantation: Historical review and clinical potential

Half a million patients in the USA alone require treatment for burns annually. Following an extensive burn, it may not be possible to provide sufficient autografts in a single setting. Pig skin xenografts may provide temporary coverage. However, preformed xenoreactive antibodies in the human recipient activate complement, and thus result in rapid rejection of the graft. Because burn patients usually have some degree of immune dysfunction and are therefore at increased risk of infection, immunosuppressive therapy is undesirable. Genetic engineering of the pig has increased the survival of pig heart, kidney, islet, and corneal grafts in immunosuppressed non-human primates from minutes to months or occasionally years. We summarize the current status of research into skin xenotransplantation for burns, with special emphasis on developments in genetic engineering of pigs to protect the graft from immunological injury. A genetically-engineered pig skin graft now survives as long as an allograft and, importantly, rejection of a skin xenograft is not detrimental to a subsequent allograft. Nevertheless, currently, systemic immunosuppressive therapy would still be required to inhibit a cellular response, and so we discuss what further genetic manipulations could be carried out to inhibit the cellular response.

Stem cells, niches and scaffolds: Applications to burns and wound care

The importance of skin to survival, and the devastating physical and psychological consequences of scarring following reparative healing of extensive or difficult to heal human wounds, cannot be disputed. We discuss the significant challenges faced by patients and healthcare providers alike in treating these wounds. New state of the art technologies have provided remarkable insights into the role of skin stem and progenitor cells and their niches in maintaining skin homeostasis and in reparative wound healing. Based on this knowledge, we examine different approaches to repair extensive burn injury and chronic wounds, including full and split thickness skin grafts, temporising matrices and scaffolds, and composite cultured skin products. Notable developments include next generation skin substitutes to replace split thickness skin autografts and next generation gene editing coupled with cell therapies to treat genodermatoses. Further refinements are predicted with the advent of bioprinting technologies, and newly defined biomaterials and autologous cell sources that can be engineered to more accurately replicate human skin architecture, function and cosmesis. These advances will undoubtedly improve quality of life for patients with extensive burns and difficult to heal wounds.