First Use of Allogeneic Stem Cells in the Treatment of Recessive Dystrophic Epidermolysis Bullosa: Demonstration of Biochemical and Clinical Improvement.

Abstract 660

Recessive dystrophic epidermolysis bullosa (RDEB) is an incurable, often fatal mucocutaneous blistering skin disease caused by mutations in the type VII collagen (C7) gene, COL7A1. These pathogenic mutations result in severely diminished expression of C7, a collagen localized at the dermal-epidermal junction (DEJ), and absence of anchoring fibrils (AFs) which are C7 containing structures that tether the epidermal basement membrane to the dermal matrix. From birth on, children with RDEB develop painful erosions and blisters on mucosal membranes and skin often resulting in esophageal strictures, mutilating scarring, joint contractures, fusion of fingers and toes and, aggressive squamous cell carcinomas. After first demonstrating that a stem cell enriched fraction of bone marrow (BM) rescued a proportion of RDEB mice from lethality and resulted in a) expression of C7 in skin and mucosal membranes, b) formation of new AFs, and c) resistance to blistering, a ‘first-in-human' phase I-II clinical trial was initiated in October 2007. To date, 7 patients have been treated with stem cells from BM from an HLA matched sibling donor (n=6) or unrelated cord blood (CB) donor (n=1). Follow-up data are reported through August 18, 2009. Conditioning consisted of busulfan 0.8 mg/kg per dose every 6 hours on days–9 to–6, fludarabine 25 mg/m²/day on days–5 to–3, and cyclophosphamide 50 mg/kg/day on days–5 to–2. After infusion of stem cells on day 0, immunoprophylaxis consisted of cyclosporine and mycophenolate mofetil. Patient and graft characteristics are shown in Table 1. Of the 4 patients with adequate follow-up, a progressive increase in C7 deposition by immunofluorescence (IF) at the DEJ, AFs or AF-like structures by electron microscopy, and wound healing with marked reduction in blister formation were documented. Unexpectedly, all patients had substantial chimerism in the skin (11-93%) that persisted over time. In 2 patients with a sex mismatched donor, perivascular localization of the donor cells in the dermis could be discerned using probes to the centromere regions of chromosomes X and Y. In summary, this is the first demonstration that the infusion of BM can ameliorate the severe systemic mucocutaneous manifestations of RDEB and sets the stage for using marrow stem cells in the treatment of a broad spectrum of extracellular matrix disorders.