Xenograft and temporary wound coverage

Overview

Xenografts are tissue grafts transplanted between species, most commonly porcine (pig) skin applied to human burn wounds. In burn care, xenografts function exclusively as temporary biologic dressings; they do not permanently incorporate into the wound and are eventually rejected by the host immune system ^[1]. Their clinical value lies in providing physiologic wound coverage that reduces pain, limits evaporative fluid loss, decreases bacterial contamination, and prepares the wound bed for definitive closure with autograft ^[2].

Porcine skin is the most widely used xenograft in burn care due to its structural similarity to human skin, commercial availability, and relatively low cost compared to cadaveric allograft ^[3]. However, xenografts are immunologically inferior to allografts, with faster rejection times and less effective wound bed vascularization ^[4].

Types of xenografts

Porcine skin

Porcine split-thickness skin xenograft is available as fresh, frozen, or irradiated product. It is typically meshed or perforated to allow wound drainage. Porcine skin adheres to partial-thickness wound beds within 24-48 hours, reduces pain substantially, and sloughs spontaneously as the wound epithelializes beneath it [2, 3].

For full-thickness excised wounds, porcine xenograft provides temporary barrier function but does not vascularize reliably. It is rejected within 7-14 days and must be replaced or the wound must be definitively closed within that interval ^[4].

Fish skin graft

Acellular fish skin (Kerecis Omega3 Wound, derived from Atlantic cod) has emerged as an alternative xenograft. A preclinical study comparing intact fish skin graft (IFSG) with porcine allograft as temporary coverage for full-thickness burns in a porcine model demonstrated that IFSG created a granulated wound bed receptive to subsequent STSG application ^[5]. Contraction rates, trans-epidermal water loss, hydration, and blood perfusion were similar between fish skin and porcine allograft groups. Fish skin grafts showed increased angiogenesis and granulation tissue formation on histology at day 7.

Genetically modified porcine skin

Research into genetically modified porcine skin aims to overcome hyperacute rejection mediated by preformed antibodies to alpha-1,3-galactose (Gal). Skin from alpha-1,3-galactosyltransferase knockout (GalT-KO) miniature swine lacks this antigen and survives as long as allograft in primate models (approximately 11 days) ^[6]. Rejection of GalT-KO xenograft does not cross-sensitize to alloantigens, meaning subsequent allograft application is not compromised [7, 8]. This technology is not yet clinically available but represents a potential future alternative to allograft.

Indications

Partial-thickness burns: Porcine xenograft applied to superficial and deep partial-thickness burns provides pain relief, protects the wound during re-epithelialization, and reduces dressing change frequency [2, 3].

Excised full-thickness burns: Temporary coverage of excised wounds when autograft donor sites are exhausted and allograft is unavailable. Xenograft buys time (5-10 days) for donor site healing before re-harvest ^[4].

Toxic epidermal necrolysis (TEN): Young et al. demonstrated that porcine xenograft in TEN patients significantly reduced intravenous fluid requirements (1.45 to 0.9 ml/kg/day/%TBSA, p=0.02), pain scores (5.5 to 2.8, p=0.03), and need for sedation during wound care compared to pre-xenograft measures and historical controls treated with silver dressings ^[9].

Donor site coverage: Xenograft can cover skin graft donor sites, reducing pain and potentially accelerating re-epithelialization, though evidence for this application is limited ^[10].

Wound bed preparation: Xenograft adherence serves as a clinical test of wound bed viability. Wounds that support xenograft adherence are typically ready for autograft or allograft ^[2].

Comparison with allograft

Allograft is biologically superior to xenograft for temporary wound coverage. Key differences:

• Vascularization: Allograft vascularizes and provides true physiologic wound closure. Xenograft adherence is primarily through fibrin bonding without reliable vascularization ^[4].
• Duration of coverage: Allograft persists 14-21 days before rejection; xenograft is rejected within 7-14 days [4, 6].
• Wound bed preparation: Allograft produces superior granulation tissue suitable for subsequent autograft compared to xenograft ^[4].
• Availability: Xenograft is commercially produced with reliable supply; allograft depends on cadaveric donation with variable availability ^[11].
• Cost: Xenograft is generally less expensive than allograft.
• Disease transmission: Both carry theoretical risk, but xenograft risk is lower due to absence of human pathogens in porcine sources.

Synthetic alternatives

Biobrane

Biobrane is a biosynthetic wound dressing composed of nylon mesh bonded to silicone membrane with porcine collagen peptides. A multicenter trial demonstrated equivalence to frozen cadaver allograft for temporary coverage of excised burns ^[12]. Biobrane is particularly useful for partial-thickness burns and donor sites.

Suprathel

Suprathel is a synthetic copolymer membrane that functions as a temporary epidermal substitute. A systematic review comparing Suprathel with porcine xenograft found significantly lower need for subsequent skin grafting and lower infection rates with Suprathel, with comparable healing times ^[3].

Biosynthetic cellulose

Biosynthetic cellulose dressings (Epiprotect) provide an alternative to xenograft without animal-derived components. Clinical experience shows outcomes comparable to porcine xenograft for both superficial burns and temporary coverage of excised deep burns, with the added benefit of pain relief on application ^[13].

Complications

Xenograft-specific complications include accelerated rejection with inflammation and purulence (particularly in immunocompetent patients with repeat applications), adherence failure in infected or heavily contaminated wounds, and rare allergic reactions to porcine proteins ^[4]. There are no documented cases of zoonotic disease transmission from processed porcine xenograft to burn patients.

Cultural and religious objections to porcine-derived products (Islamic, Jewish, Hindu, and some vegetarian populations) require sensitivity and alternative coverage options ^[13].

Controversies and Evidence Gaps

The role of porcine xenograft relative to newer synthetic alternatives (Suprathel, biosynthetic cellulose) is evolving. Evidence suggests synthetic products may offer comparable or superior outcomes for partial-thickness burns, potentially making xenograft less relevant for this indication ^[3].

The clinical potential of genetically modified porcine skin (GalT-KO) to serve as a functional equivalent to allograft has been demonstrated in primate models but has not progressed to clinical trials [6, 7].

Fish skin grafts represent a novel approach with early promising data but require validation in human clinical trials for burn-specific applications ^[5].

The comparative cost-effectiveness of xenograft versus synthetic alternatives has not been systematically evaluated across different clinical scenarios and healthcare systems.

References

[1] Yamamoto T et al. (2018). Skin xenotransplantation: historical review and clinical potential. Burns. 44(7):1738-1749. PMID: 29602717 [2] Chiu T et al. (2005). "Xenograft" dressing in the treatment of burns. Clin Dermatol. 23(4):419-23. PMID: 16023938 [3] Haller HL et al. (2021). Porcine xenograft and epidermal fully synthetic skin substitutes in the treatment of partial-thickness burns: a literature review. Medicina. 57(5):432. PMID: 33946298 [4] May SR (1991). The effects of biological wound dressings on the healing process. Clin Mater. 8(3-4):243-9. PMID: 10149129 [5] Stone R et al. (2024). Comparison of intact fish skin graft and allograft as temporary coverage for full-thickness burns. Biomedicines. 12(3):680. PMID: 38540293 [6] Leto Barone AA et al. (2014). Genetically modified porcine split-thickness skin grafts as an alternative to allograft: preliminary characterization. Burns. 41(3):565-74. PMID: 25406888 [7] Albritton A et al. (2014). Lack of cross-sensitization between GalT-KO porcine and allogeneic skin grafts permits serial grafting. Transplantation. 97(12):1209-15. PMID: 24798308 [8] Mastroianni M et al. (2018). Topical delivery of immunosuppression to prolong xenogeneic and allogeneic split-thickness skin graft survival. J Burn Care Res. 39(3):363-373. PMID: 28639977 [9] Young JB et al. (2016). The use of porcine xenografts in patients with toxic epidermal necrolysis. Burns. 42(8):1728-1733. PMID: 27350163 [10] Kitala D et al. (2020). Porcine transgenic, acellular material as an alternative for human skin. Transplant Proc. 52(7):2218-2222. PMID: 32684370 [11] Saffle JR (2009). Closure of the excised burn wound: temporary skin substitutes. Clin Plast Surg. 36(4):627-41. PMID: 19793557 [12] Purdue GF et al. (1987). Biosynthetic skin substitute versus frozen human cadaver allograft for temporary coverage of excised burn wounds. J Trauma. 27(2):155-7. PMID: 3546711 [13] Karlsson M et al. (2019). Three years' experience of a novel biosynthetic cellulose dressing in burns. Adv Wound Care. 8(2):71-76. PMID: 30809423