Can Skin Cells Improve Outcomes for Patients With Deep Burns?

Reference: Gardien KL, Marck RE, Bloemen MC, Waaijman T, Gibbs S, Ulrich MM, Middelkoop E; Dutch Outback Study Group 1. Outcome of burns treated with autologous cultured proliferating epidermal cells: a prospective randomized multicenter intrapatient comparative trial. Cell Transplant. 2016;25(3):437–448. doi:10.3727/096368915X689569

Rationale: No engineered skin substitute had been shown to improve outcomes of patients with full-thickness burns beyond those obtained using unmeshed STSG. Favorable case study results suggested the merit of comparing outcomes of covering an STSG with proliferating cultured autologous mixed epidermal cells (ECs) with those using STSGs in a RCT. 

Objective: A prospective multicenter RCT compared outcomes for up to 1 year following STSG grafting of paired full-thickness burn sites on patients whose STSGs were covered or not covered with autologous proliferating cultured ECs in an elastin-coated collagen carrier. 

Methods: With appropriate institutional protocol approval and patient consent, investigators at 3 Dutch burn centers enrolled 40 patients of at least 18 years of age, each with a full-thickness burn measuring an area of 100 cm² to 300 cm². Enrollment was from June 2008 to September 2012, except during culture facility updates at 1 center in September 2010 to October 2011. Pateints who were immunocompromised or infected, those on cytostatic drugs or greater than or equal to 20 mg/pd of corticosteroid, or those medically judged incapable of following the protocol were excluded from the study. Patients’ burn sites received standardized topical 1% silver sulfadiazine cream over an average of 13 days before surgery, applying an STSG meshed to an expanded ratio of 1:3 to 2 comparable sites on each patient. One randomly assigned site received the STSG alone. The other STSG was covered with an EC/carrier complex with the EC side down. The EC consisted of proliferating keratinocytes and melanocytes obtained from the same patient’s biopsy then seeded at a density of 50 000 cells/cm² onto a collagen/elastin carrier grown for 2 to 5 days to form a histologically verified cell monolayer on the carrier. One day before STSG surgery was planned, the EC/carrier complex was sterilely transported under ambient conditions from the culture facility to the operating room. The STSG and its EC cover were held in place with staples, then covered with a nonadhesive dressing. The primary outcome was wound healing, monitored by an experienced burn specialist from the first dressing change 5 to 7 days postoperatively until complete healing; wound healing was calculated as the percent of the wound area epithelized. Visibility of the EC carrier unblinded early healing observations. Graft take was rated based on adherence to the wound bed and graft vitality during wound healing observations. Swab cultures documented bacterial contamination preop and postop. Scar quality was rated 3 and 12 months postop using the reliable, validated Patient and Observer Scar Assessment Scale (POSAS), in which patients rated pain, color, itching, stiffness, thickness, and surface irregularity; observers rated vascularization, pigmentation, thickness, relief, pliability, and surface area. Scores were on a 1-point to 10-point scale summed to make a total scar score of 6 to 60. Scar erythema (vascularization) and pigmentation (melanin) were measured using appropriate spectra on a dermal spectrometer. Scar elasticity was measured as deformation of a defined circle of scar under a controlled vacuum. The sample size of 40 patients was determined from prior results to meet statistical criteria of 90% power and P = .05 for statistical significance, with extra patients added to compensate for withdrawals and complications. Analyses of normally distributed continuous data used the paired t test. Wound contamination trends were tested using chi-squared tests. Wound healing and POSAS score differences were tested using the nonparametric Wilcoxon test.

Results: Most patients were men with flame burns covering a mean of 29% TBSA (range, 6%–51% TBSA). Intent-to-treat (ITT) analysis was not used due to withdrawal of 4 patients caused by: (1) complete healing, (2) death before the planned STSG procedure, (3) fungal contamination, or (4) slow cell division of the EC culture. Postoperatively, most STSG graft sites were dressed with a 1% silver sulfadiazine tulle dressing with no other topical medication. The EC carrier served as the dressing for EC-dressed sites. Sites dressed with the added EC layer were 71% epithelized at 5 to 7 days postoperatively as compared with 67% epithelized with STSG alone (P = .034). There were similar rates of graft take (89% or 90%), wound contamination, reoperation, and length of hospital stays, with no treatment-related adverse events in either group. Total POSAS scar quality scores at 3 months after grafting were rated better for EC sites by observers (P = .001) and marginally so (P = .084) by patients, with greater elasticity (P = .030). At 12 months, POSAS trends were better for EC-treated STSG sites for clinician observers (P = .020) and for patients (P = .024) and were accompanied by more normal skin color (erythema, P = .025; melanin, P = .011) with similar elasticity as compared with STSG sites.

Authors’ Conclusions: For patients with large-area, full-thickness burns, covering standard STSGs with proliferating EC in a compatible carrier safely reduced wound healing time and improved subjectively and objectively measured scar quality at 3 and 12 months postoperatively.

Reference: Holmes Iv JH, Molnar JA, Carter JE, Hwang J, Cairns BA, King BT, Smith DJ, Cruse CW, Foster KN, Peck MD, Sood R, Feldman MJ, Jordan MH, Mozingo DW, Greenhalgh DG, Palmieri TL, Griswold JA, Dissanaike S, Hickerson WL. A comparative study of the ReCell® device and autologous split-thickness meshed skin graft in the treatment of acute burn injuries. J Burn Care Res. 2018;39(5):694–702. doi:10.1093/jbcr/iry029

Rationale: The clinical benefits of early excision and grafting of deep partial- and full-thickness burns are widely recognized but offset by morbidity related to the large area of the STSG donor sites. An autologous skin cell suspension (ASCS) from a point-of-care device improved deep partial-thickness burn pain with healing similar to that provided by meshed STSG.

Objective: The authors conducted a multicenter, same-patient RCT comparing healing of deep partial-thickness burns covered with an STSG or ASCS, testing comparability of grafted burn site healing times and significance of differences for respective donor site healing times to explore the use of the ASCS as an alternative to STSG grafting. 

Methods: With appropriate patient consent and institutional review board approval, this noninferiority study was performed at 12 burn centers in the United States between May 2010 and August 2014, under a US Food and Drug Administration Investigational Device Exemption. Power calculations determined that at least 42 paired sites were needed for the study. This was increased to allow for withdrawals and protocol violations, enrolling 101 patients between the ages of 18 to 65 years, each with an acute, deep partial-thickness burn covering 1% to 20% TBSA of sufficient area to accommodate 2 separate or contiguous 100 cm² to 320 cm² grafts. One similar site each was randomly assigned to receive either a 2:1 meshed STSG or a similar area of ASCS. Patients were excluded if they had a pre-existing local or systemic infection or other condition that may delay wound healing or preclude participation; if they were using antibiotics, steroids, or other agents that may affect wound healing; or if their burns were caused by chemicals, electricity, or radiation. No study burn site was located on the head, neck, face, feet, hands, joints, or genitalia. The STSG was harvested 2 to 19 days after injury, placed on sterile saline-moistened gauze until use, and then held in place on the graft site with sutures or staples. The ASCS was prepared from an autologous split-thickness skin sample and trimmed to an area of less than 4 cm² to cover a graft site of up to 320 cm². Both graft sites were covered primarily until the first graft site observation 6 to 8 days postoperatively with a nonadherent, low-absorbent, small-pore, clear primary dressing also used to dress the skin graft donor sites. Secondary petrolatum-gauze dressings on both graft sites were changed as needed. Both graft sites were assessed at weeks 1, 2, 3, 4, 8, and 16 following surgery. The primary endpoint was percent of treated sites greater than or equal to 95% reepithelized by week 4 postoperatively, with a non-inferiority margin of 10%, based on clinical observation. Secondary endpoints were patient-reported pain at weeks 1 through 16 and graft site visual appearance assessed on weeks 16, 24, and 52, both measured on the visual analogue scale. Clinicians rated scar appearance of both sites at weeks 16, 24, and 52 using the Vancouver Scar Scale. The ITT analysis of all 101 randomized patients was performed for healing, safety, scarring, and demographic parameters. McNemar’s test of equality of paired proportions with a 2-sided Type 1 error (of incorrectly rejecting the hypothesis of no between-treatment difference) was set at P ≤ .050, indicating significance of healing or scar differences. 

Results: Most graft sites were due to flame burns on male patients, with an average patient age of 39.5 years. Graft surgery and treatment occurred at a mean of 7.1 days postburn, allowing time to discern that autografting was medically indicated. Of the 101 randomized patients, 87 completed the protocol to 52 weeks after autograft without major protocol deviations. Baseline autograft areas were comparable (STSG, 168 cm²; ASCS, 165 cm²). Average donor site area was much smaller for ASCS (4.7 cm²) compared with STSG (194.1 cm²). The ASCS reduced donor site area by 97.5% (P = .0001). At 4 weeks postoperatively, incidence of graft site healing to 95% reepithelization was statistically noninferior for ASCS (97.5%) compared with STSG (100%), while that for donor sites was superior for ASCS at weeks 1 (P = .04) and 2 (P < .001). No episodes of late wound breakdown were observed for either intervention, but there were 26 skin and subcutaneous adverse events in the ASCS graft sites, mainly related to a lack of a topical protective dressing or to use of silver sulfadiazine, as compared with 16 similar events for STSG sites (P = .0129). Pain for STSG and ASCS graft sites was comparable through week 16 as were patient satisfaction with ASCS donor site appearance and investigator-rated Vancouver Scar Scale scores through week 52 postoperatively. Donor site pain was less for ASCS as compared with STSG sites through week 16, and donor site appearance and Vancouver Scar Scale ratings were better for ASCS sites through week 52 (P < .05). 

Authors’ Conclusions: The STSG and ASCS grafting of excised deep partial-thickness burns had comparable healing and scarring results, with improved pain, healing, and scarring of the much smaller ASCS donor sites. While protection of the grafted site is vital, ASCS has potential to use less donor skin.

It has been almost 50 years since the pioneering discovery that early excision and immediate grafting improved outcomes for those with deep burns.⁷ Key factors limiting outcomes for these patients include time to grafting and limited available areas of intact donor skin. The 2 studies reviewed herein^5,6 are good examples of clinical evidence advancing the field by reporting reliable, valid, clinically relevant improvements in patient-centered outcomes. A 3-cm² biopsy provided sufficient EC/complex to cover 300 cm² of full-thickness burn site, effectively reducing the time to graft healing, but this procedure still requires the same area of STSG donor sites for patients to heal.⁵ Without requiring an STSG, the ASCS afforded comparable healing to a meshed 2:1 STSG graft site, while greatly reducing the required area of intact autologous donor skin needed to harvest the noncultured ASCS.⁶ Further studies are needed to determine if the latter finding on deep partial-thickness burns holds for full-thickness burns like those studied by Gardien et al.⁵ Reviewing these 2 techniques together makes one wonder if they may be used in stages or in synergy. For example, as soon as patient with the full-thickness burn is stabilized and the burn is excised in the burn center, a tiny donor site could provide ASCS to seed autologous cells onto the burn excision surface, populating areas of questionable depth. Might this reduce the donor site area needed for subsequent STSG procedures for areas in which the ASCS does not thrive? Could a portion of the ASCS sample be processed and cultured on the EC collagen/elastin carrier to cover subsequent meshed STSG(s), thereby reducing their healing time? Imagine the patient benefits of earlier grafting using smaller donor site areas with the same improvements in healing and scarring as the EC. The STSG donor sites also could benefit from broader clinical use of the long-standing strong evidence supporting STSG donor site healing 7 days faster using hydrocolloid dressings as compared with any other dressings, while limiting pain and infection rates.^8,9 It is exciting to see sound research laying the foundations for further improvement of outcomes for those with full-thickness or deep partial-thickness burns. 

Author: Laura Bolton, PhD

Affiliation: Adjunct Associate Professor, Department of Surgery, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ