What did this project achieve?
Allogeneic Blood & Marrow Transplantation (Allo-BMT) offers the best potential for cure for numerous malignant and non-malignant diseases, and has been in clinical trials in multiple centers, including ours, to treat the recessive dystrophic form of EB (RDEB). Despite promising results that have been obtained from both preclinical and clinical studies, many questions remain to be answered before an effective cure can be reached. A major question is what the effective cells are in the blood or marrow, and whether these cells can be isolated and used as an off-shelf product by itself or co-administration with blood or bone marrow. Here we evaluated the effect of a novel stem cell type isolated from human umbilical cord blood (HUCB), named as unrestricted somatic stem cells (USSCs) on wounding, which occurs constantly in patients with RDEB. We showed that USSCs share important features with human embryonic stem (ES) cells, in terms of their expression of ES transcription factors. In addition, USSCs exhibit an intermediate level of chromatin modification (in this case, DNA methylation) on the genes encoding these transcription factors, between human ES and more differentiated cells. This forms the basis for HUCB-derived USSCs’ plasticity in tissue regeneration (the ability to give rise to multiple cell types), yet without the safety concern associated with ES cells (potential in vivo uncontrolled differentiation, i.e., formation of teratoma). We demonstrated that USSCs express COL7A1, the protein that is lacking in patients with RDEB. This suggests that once USSCs reside in the skin of RDEB patients, they could potentially rescue the defective anchoring fiber formation by secreting COL7A1. We also showed that USSCs express CCR2, the receptor for macrophage inflammatory protein (MIP-alpha), that is highly expressed in dermal wounds. This implies that under inflammatory conditions such as RDEB patients constantly have on the skin, transplanted USSCs could be able to migrate to the sites of blistering. We therefore hypothesized that when exposed in vivo, USSCs may have the abilities to give rise to multiple skin cell types and/or promote wound healing by excreting various proteins or growth factors (paracrine effects). As a starting point to investigate the role of USSCs in relieving RDEB disease, we evaluated the effects of USSCs on promoting wound healing in a mouse wound healing model. We created a 1cm2 full thickness wound at the dorsal of each immunocompromised mouse. Four hours after wounding, 1 million USSCs or PBS negative control was injected at a single injection site 0.8-1cm away from the margin of the created wound. The wounds were photographed daily among the experimental groups and the areas of the wounds were quantitated using Image J to compare the rate of wound closure. In around two weeks, wounds almost closed among all the wounded mice. However USSC-treated wounds closed at a faster rate as compared to PBS and there was a statistically significant difference between USSC and PBS treatment on days 6-10 after wounding. The microscope (histological) evaluations on the sections of the wounds taken at different time Umbilical Cord Blood Multi-lineage Stem Cells In The Treatment Of Recessive Dystrophic Epidermolysis Bullosa PI: Cairo, M.S. 13 points (day 3, day 8, day 16, week 4, week 5 and week 6), all demonstrated a better wound healing with
USSC-treated wounds as compared to the same time points for PBS control, as determined by the progressionof epithelialization, formation of epidermis and degree of fibrosis etc. Three days after injection, we detected a significant number of human cells only within the wounded area, but not within the unwounded skin surrounding the wounds. Moreover, there were also more human cells in the wound that was in proximity to theinjection site than in the distal site. This indicates the migration of the cells from the injection site, through the unwounded skin and to the wounded area. Interestingly, three days after injection, the human cells were found mainly in the area closely underneath the surface of the wound, implying its role in re-epithelialization of the wound. However, at later time points, the human cells can only be detected within the basal membrane in the healed skin.
One interesting phenomena we have observed is the presence of skin appendages (i.e., hair follicles, sebaceous glands) in the wounded center in mice treated with USSCs only, but not PBS or human dermal
fibroblasts. These structures started to appear on day16 wounded skin samples and become much more apparent on week 6 wounded skins. The data demonstrate that USSCs are able to promote regeneration of functional skin.
In summary, we have shown that HUCB-derived USSCs promoted wound healing. USSCs have the ability to migrate specifically to the wounded area, promote epithelialization and facilitate the formation and remodeling
of epidermis. The resultant USSC-treated skin was less fibrotic and showed presence of skin appendages with normal morphology. It is likely that USSCs promoted wound healing by both secretion of growth factors to stimulate local regeneration and their engraftment in the skin. We are now determining specific function of the engrafted human cells. Based on the above observation, we speculate that USSCs would improve the blistering phenotype in the skin with RDEB. Moreover, their specific migration to the wounds and the ability to synthesize COL7A1 are also likely to generate positive effects on rescuing the genetic defects of RDEB. We have now generated a USSC cell line that expresses reporter gene (green fluroresence and bioluminescence), which will allow us to track in real-time the transplanted cells in experimental animals using non-invasive imaging approaches. Our next goal is to determine the ability of USSCs in rescuing the phenotypes of RDEB in an animal model, using the approaches proposed above.