Immune tolerance of allogeneic haematopoietic cell transplantation supports donor epidermal grafting of recessive dystrophic epidermolysis bullosa chronic wounds

Abstract

Background: Chronic wounds, a common morbidity in recessive dystrophic epidermolysis bullosa (RDEB), lack definitive therapies.

Objectives: To assess allogeneic epidermal skin grafts in terms of wound healing and durability over time.

Methods: In a prospective, open-label clinical trial for postallogeneic haematopoietic cell transplantation (post-alloHCT) patients with RDEB, up to nine chronic wounds per patient were grafted over 1 year. Epidermal grafts measuring 5 cm2 were obtained from related alloHCT donors in the outpatient setting using the CELLUTOMETM Epidermal Harvesting System. Wounds were photographed and symptom inventories completed at baseline and 6, 12 and 52 weeks after grafting. The trial was registered at ClinicalTrials.gov (NCT02670837).

Results: Between August 2016 and January 2019, eight patients with RDEB received a total of 35 epidermal allografts at a median of 1157 days (range 548-2884) post-alloHCT. The median (interquartile range) percentage reductions in wound surface area were 75% (52-94), 95% (72-100) and 100% (97-100) at 6, 12 and 52 weeks postgraft, respectively, each significantly reduced from baseline (P < 0·001). Donor harvest sites healed quickly without scarring. Biopsy evaluation at 1 year of an epidermal allograft site revealed wildtype type VII collagen (immunofluorescence), anchoring fibrils (electron microscopy), and full-thickness skin whole-DNA donor chimerism of 42% (compared with 16% in concurrently biopsied native skin). This strategy subsequently supported release of RDEB pseudosyndactyly.

Conclusions: The immune tolerance established by alloHCT supports successful adoptive transfer of donor epidermal grafts. Persistence of donor grafts in a single patient beyond 1 year and observed migration of donor-grafted cells into adjacent wound suggest that epidermal allografts include nonterminally differentiated cells and/or trigger recruitment of donor bone-marrow-derived cells to mediate wound healing.

Conflict of interest statement

Conflicts of Interest: The authors have no conflicts of interest to disclose.

© 2020 British Association of Dermatologists.

Figures

Figure 1.. AlloHCT establishes immune tolerance for donor epidermal graft.

With alloHCT, the RDEB patient immune system transitions to that of the unaffected donor. This establishes immune tolerance allowing for subsequent skin grafts from the same donor to heal chronic wounds of the patient with RDEB.

Figure 2.. Wound closure with epidermal allografting over one year.

Figure 2a shows a selected example of epidermal allograft placement and wound closure (large back wound of Patient 5), with quantification of wound surface area on replicate images. Black outlines the epidermal graft at baseline/graft placement and open wound available for wound closure beneath the epidermal allograft at all timepoints. Residual wound is outlined in light blue at week 6, dark blue at week 12 and green at week 52. For individual wounds, the percent reduction in wound size over one year following epidermal allografting is displayed in Figure 2b (median and IQR boxplot), statistically significantly reduced at all timepoints compared to baseline, p

Figure 2.. Wound closure with epidermal allografting over one year.

Figure 2a shows a selected example of epidermal allograft placement and wound closure (large back wound of Patient 5), with quantification of wound surface area on replicate images. Black outlines the epidermal graft at baseline/graft placement and open wound available for wound closure beneath the epidermal allograft at all timepoints. Residual wound is outlined in light blue at week 6, dark blue at week 12 and green at week 52. For individual wounds, the percent reduction in wound size over one year following epidermal allografting is displayed in Figure 2b (median and IQR boxplot), statistically significantly reduced at all timepoints compared to baseline, p

Figure 3.. Epidermal allograft microarchitecture resembles control skin with intact C7 and anchoring fibrils at 1-year post-epidermal allograft (two years post-alloHCT).

Skin biopsies of Patient 4 native skin (a) and epidermal graft site (b), compared to an unaffected control (c). Immune electron microscopy images on the left. Main images without immune label, arrows highlight anchoring fibrils, scale bar = 500 nm. Inserts with C7 immunolabels, left lower insert with LH24, right lower insert with mAb185, scale bar = 200 nm. Immunofluorescence images on the right with four C7 antibodies and two control antibodies, Type IV collagen and fibrillin, shown in red and DAPI nuclear staining in blue (40× magnification).

Figure 4.. Epidermal allografts aid bilateral pseudosyndactyly release.

Serial photographs of the palmar surfaces of Patient 5’s hands following use of epidermal allografts for closure of skin defects during pseudosyndactyly release.