The goal of this project is to generate normal skin, containing functional, properly patterned hair to treat victims of burns, trauma or disease such as alopecia (loss of hair). The Principle Investigator (PI) has developed an assay (“planar hair forming procedure”) using a slurry of dissociated and re-aggregated newborn mouse skin cells on a scaffold that can engraft onto a wound bed and generate apparently normal hair. The PI proposes 3 aims utilizing the mouse skin cell assay, and a fourth aim to translate the findings to human cells. In the first aim, the existing assay will be optimized by altering the ratio of epidermal to dermal cells and by utilizing different matrices. In the second aim, the number and size of the resulting hair follicles will be optimized, by manipulating the cells and the graft environment using various growth factor conditions and small molecules. Some active compounds have already been discovered and others will be identified. The goal of the third aim is to track the fate and location of grafted cells, using various imaging methods and to evaluate the generation of teratomas. In aim four, attempts will be made to determine whether human embryonic stem cells (hESC), human induced pluripotent stem cells (hiPSC), other human cells, or their derivates can be used to generate grafts of normal skin with hair, using assays similar to the ones described for newborn mouse skin cells.
This is a well-written proposal targeting an important clinical problem that the PI plans to address using an interesting tissue engineering approach. However, reviewers identified several issues that reduced their enthusiasm for this application. First, they were not convinced that an emphasis on normal hair pattern is justified when considering approaches for treating burn victims. While the desire for “normal” skin is obvious, generation of healthy skin with imperfect hair patterning may still be very useful for treating burn victims. Second, reviewers considered it a major problem that very little consideration is given to the stem cell biology of the “planar hair forming procedure”, calling the responsiveness of this application to the RFA into question. Although the PI proposes to track the fate of stem cells in the graft, the proposed approach is flawed in that labeling of the cells to be tracked does not target stem cells, but rather will label all cells in the transplanted cell mixture. While this is useful for evaluating the graft, it is not helpful for understanding its stem cell biology. The study would have gained in significance if some of the reporter genes for cell tracking were to be placed under the control of a cell type-specific promoter. The experiments in the final aim are based on stems cells in that they seek to determine whether hESC or hiPSC, amongst other human cells, can be used to generate skin and hair forming cells, but it remains unclear how this is related to the mouse work proposed for aims 1 through 3, and whether the derivatives will have hair-forming potential similar to that of mouse skin samples.
The proposed optimization of the graft in the first two aims is well thought out and supported by strong preliminary data, although one reviewer felt not enough information was provided about the composition of the slurry. Overall, as presented, the assay seems to be quite robust, and it was not obvious to the reviewers what needs to be optimized. With regard to aim 3, the reviewers appreciated that due to its surface transplantation, the skin patch paradigm is uniquely suited for non-invasive imaging to follow the fate of cells over time. Therefore, reviewers felt that much can be learned about the behavior for transplanted cells, which may have wider implications for the field. For instance, discoveries related to early processes of teratoma formation based on monitoring early dysplastic or malignant changes could be applicable to teratomas formed by other stem cells. A reviewer pointed out, though, that the applicant discussed analysis of teratoma formation in the context of the transplants involving newborn mouse skin cells, when teratoma formation is not expected. The applicant proposes to use various relevant imaging modalities, but did not provide a rationale for the use of PET imaging, when the use of bioluminescence and GFP imaging seems sufficient. Reviewers further pointed out that this proposal is presented as addressing a bottleneck, identified by the PI as the “long-term care of burn victims”, but felt that instead this project pursues a development candidate, i.e. skin with normal hair.
The PI is highly qualified to lead this translational research team, is an expert and long-time contributor to the field of hair follicle patterning and has published extensively. Many of his/her studies have used the avian feather model, while recent work has also shed light on the molecular regulation of hair follicle regeneration in the mouse. The strong multi-disciplinary research team includes investigators with interests in skin and hair and with expertise in surgery and imaging, with small molecule screens, hESC and hiPSC work. However, the roles of the stem cell biologists are rather poorly developed, and it would have been helpful if there were a clear experimental strategy for using hESC in this work. The stem cell environment at the applicant institution is very strong. The PI has adequate resources and research facilities to conduct the experiments and clinical connections to make the transition to human studies.
In summary, reviewers felt that the applicant proposes an interesting tissue engineering project that addresses a very important clinical problem. However, enthusiasm was reduced because this proposal is not particularly focused on stem cell biology, and it remained unclear how the planar hair forming procedure will be translated toward a stem cell-based clinical therapy. Additional concerns about experimental details contributed to an overall moderate level of enthusiasm.