Genetic skin diseases constitute a diverse group of several hundred diseases that affect up to 2% of the population and include common disease such as psoriasis, atopic dermatitis, and wound healing. Patients with one genetic disease, dystrophic Epidermolysis bullosa (EB), lack a normal collagen VII (COL7A1) gene and suffer from debilitating blistering and scarring that can be lethal by young adulthood. The disease is devastating and despite all efforts, current therapy for DEB is limited to wound care. For recessive dystrophic EB (RDEB) where there is no COL7A1 protein, our EB Disease team has shown that retroviral delivery of the COL7A1 provides a powerful disease modifying activity as autologous, cell-based therapy. While successful, our initial approach cannot treat many dominantly inherited diseases such as dominant dystrophic EB (DDEB) where a poison subunit inhibits the function of the normal protein. Recent development of induced pluripotent stem (iPS) cells that are generated from the somatic cells of individual patients could provide an ideal source of therapy. Because of recent advances by our team and others in stem cell technology, our hypothesis is that we can create genetically-corrected iPS cells for dominant skin diseases such as DDEB. The goal of the EB Disease team is to complete the RDEB IND filing and then develop a next generation skin stem cell therapeutic for DDEB, based on defined genetic correction of the patient's mutation.
The project includes increasing the efficiency of iPS cell generation from patients cells, enhancing COL7A1 homologous recombination in iPS cells to correct the defect, and then improving the ability to return iPS cells back to skin keratinocytes. We will do extensive testing of the iPS-derived skin cells using human skin tissue models to ensure the safety and efficacy of these cells. Finally, we will work together with the FDA and the our collaborator Good Manufacturing Practice facility to generate patient-specific skin grafts for each patient in the clinical trial.
If successful, the approach in this project could be used to correct genetic defects in skin and other organs. The ability to therapeutically reprogram and replace diseased skin would allow this procedure to develop therapeutic reprogramming approaches for a variety of both common and life-threatening skin diseases. Moreover, genetically-corrected pluripotent iPS cells could form the basis of future systemic therapies to other organs besides the skin to treat common genetic disorders.
Genetic skin diseases constitute a diverse group of several hundred diseases that affect up to 2% of the population and include common disease that affect Californians such as psoriasis, atopic dermatitis, and wound healing. Patients with one genetic disease, dystrophic Epidermolysis bullosa (EB), lack collagen VII (COL7A1) and suffer from debilitating blistering and scarring that can be lethal by young adulthood. The disease is devastating and despite all efforts, current therapy for DEB is limited to palliative wound care.
For recessive dystrophic EB (RDEB), our EB Disease team has shown that retroviral delivery of the COL7A1 provides a powerful disease modifying activity as autologous, cell-based therapy. While successful, our initial approach is unable to treat many common, dominantly inherited diseases such as dominant dystrophic EB (DDEB). Recent development of induced pluripotent stem (iPS) cells that are generated from the somatic cells of individual patients could provide an ideal source of therapy. Our hypothesis is that we can develop genetically-corrected iPS cells for dominant skin diseases such as DDEB. The goal of the EB Disease team is to complete the RDEB IND filing and develop a next generation skin stem cell therapeutic for DDEB, based on defined genetic correction of the patient's mutation. The skin is an ideal tissue in which to initially try stem cell therapy because it is readily accessible, straightforward to observe, and any abnormal cells can be easily excised.
The project includes establishing a bank of DDEB cells from patients, and then increasing the efficiency of non-viral iPS cell generation, COL7A1 homologous recombination in iPS cells, and keratinocyte differentiation protocols. We will do extensive testing of the iPS-derived cells using human skin tissue models to ensure the safety of these cells. Finally, we will work together with the FDA and the our collaborator Good Manufacturing Practice facility to generate skin grafts for patients in the clinical trial.
If successful, the approach in this project could be used to correct many other genetic defects. The ability to therapeutically reprogram and replace skin would allow this procedure to develop therapeutic reprogramming approaches for a variety of both common and life-threatening skin diseases, bringing an enormous benefit to the people of California. Moreover, because a by-product of this project is corrected iPS cells that are pluripotent, patient-specific corrected iPS cells could form the basis of future systemic therapies to other organs besides the skin to treat common genetic disorders.
The primary objective of this proposal is to develop a first-in-class induced pluripotent stem (iPS) cell-based therapy for the treatment of dominant dystrophic epidermolysis bullosa (DDEB), a genetic disorder in which a detrimental mutant form of the COL7A1 gene causes debilitating skin blisters. To achieve this objective, the investigators plan to develop clinically relevant methodology for deriving DDEB patient-specific iPS cells, followed by replacing mutant COL7A1 with a normal version of the gene by homologous recombination. They will then differentiate the corrected iPS cells into basal keratinocytes capable of long-term contribution to the epidermis for the purpose of making sheet grafts for patient application. To accomplish these goals, the investigators propose to generate a library of patient-specific DDEB iPS cells using non-viral methods and to optimize existing protocols for homologous recombination and keratinocyte differentiation from pluripotent stem cells. Next, the efficacy and toxicity of derived keratinocytes will be evaluated in a human tissue model of DDEB. Finally, preclinical scale up and regulatory compliance activities will be undertaken, thereby culminating in the submission of an Investigational New Drug (IND) application. In addition to these primary goals, the investigators propose activities to facilitate the approval of an IND that they have already submitted for treating recessive DEB (RDEB), which is caused by a loss of function mutation in the COL7A1 gene. For this indication, they are using retroviral delivery of a functional COL7A1 gene into patient-derived keratinocyte stem cells. This strategy, which uses adult stem cells and random DNA integration without removal of the non-functional gene, cannot be used to treat DDEB, which requires targeted replacement of the defective gene and the clonal expansion capacity of pluripotent stem cells. The applicants suggest that the cell therapy trial for RDEB (using other funds) will be useful for guiding IND development for DDEB.
Reviewers agreed that this project is highly significant for two important reasons. First, it addresses an unmet medical need for DDEB; and second, any discoveries made through this effort could markedly advance the use of iPS cell-derived therapies in general. Reviewers felt that the plan is logical, based on outstanding science, and theoretically feasible. However, several technical hurdles still need to be overcome, including a convincing demonstration of disease-modifying activity of the potential product. Thus, this project suffers from a lack of maturity. Despite this concern, the reviewers believed that if given enough time, the excellent applicant team could achieve its goals. After a rigorous programmatic discussion, the reviewers ultimately decided to recommend this high risk proposal for funding due to its enormous potential for reward.
This is an interesting and very well written proposal with the goal of treating a devastating genetic disorder whose current therapy is limited to palliative wound care. Although DDEB is rare, the successful completion of the proposed project would mark a huge milestone in the use of the new iPS cell technology. Theoretically, patient-specific genetically corrected iPS cells could be applied to treat other common genetic disorders, thereby broadening the potential impact of this work. The relative accessibility of skin makes it an attractive target to test this approach because of its accessibility for grafting, ease of observing results, and ability to treat or rapidly excise any abnormal tissue, including possible teratomas. However, the need to repair large areas of the individual’s epidermis, perhaps ultimately over the entire body, increases the challenge.
Overall, although reviewers thought that the proposed project is very ambitious, they judged the proposed experiments to be well designed and appreciated the inclusion of alternative backup plans. The applicant presents substantial proof of concept data for the treatment of the related disease RDEB. While the RDEB approach represents a different cellular and different gene manipulation paradigm than that proposed for the DDEB indication, these data illustrate that the team already has the technical expertise for the preclinical efficacy and safety studies. The applicant further presents data that the team has mastered the standard methods required for generating the proposed DDEB cell product. While these achievements were reassuring, the reviewers were nevertheless concerned that essentially none of the specific proposed cellular and genetic manipulations have yet been achieved, and all are potentially problematic. These challenges include production of patient-specific iPS cells from DDEB patients and use of reprogramming methods with no or minimal alteration of the cells’ DNA. Similarly, homologous recombination has not yet been accomplished at the COL7A1 locus in human embryonic stem cells (hESC) or iPS cells, and neither has differentiation of keratinocytes from hESC or iPS cells without the aid of DNA-integrated reporter genes. If keratinocytes cannot be efficiently generated, the investigators propose to pursue the generation of mesenchymal lineages from iPS cells. However, it was not clear how this change would impact the cell delivery method or design of the clinical trial. Finally, reviewers criticized the lack of evidence to support the disease-modifying activity of the proposed product. At minimum, the applicant could have already addressed whether keratinocytes produced from normal hESC or iPS cells can successfully replace diseased cells in an in vivo model of DDEB. Thus, while the overall science is well conceived and may ultimately prove feasible, the proposal includes multiple difficult steps that are far from routine. Most reviewers believed that there is a high likelihood of success in the long term, but also thought that this project is insufficiently mature to yield an IND within four years.
Beyond these technical challenges, the reviewers discussed several issues relating to safety. Specifically, they felt it would be necessary to determine what level of cell purification and analysis would be required to eliminate the risk of teratomas by undifferentiated iPS cell contaminants and verify the absence of acquired genetic aberrations. Moreover, in contrast to the applicant, a reviewer argued that potential immune complications need to be considered, since it is conceivable that previously hidden epitopes on the normal protein may become exposed following removal of the mutant protein, which in turn may elicit an immune response. In order to be prepared for that possibility, the reviewers thus recommended inclusion of an immune suppression plan.
Overall, the development plan is well thought out and many of the potential obstacles have been addressed. While most of the proposed milestones and Go-No Go triggers were well defined and appropriate, a few of them were considered incomplete. For example, it was unclear to the reviewers how and when the investigators would decide to pursue iPS cell-derived mesenchymal cell populations rather than keratinocytes. A strength of this proposal lies in the fact that the team has already completed all the pre-IND processes for a cellular product to treat RDEB, and their GMP facility has developed scaled production methods for growing epidermal sheets. Therefore, some of the processes and reagents have already been established for the RDEB program and will be directly applicable to this DDEB project. However, reviewers did not think it was justified to include obtaining approval for the already submitted RDEB IND in the present application. Reviewers also emphasized that the RDEB IND does not bear on the approval process for an iPS cell-derived therapy, which is very new to the Food and Drug Administration (FDA). They felt that it is very likely the FDA had not yet evaluated such an approach, and the applicant is advised to engage the FDA very early on to discuss proposed reprogramming methods and to confirm preclinical safety studies.
The principal investigator (PI) and co-PIs are highly qualified and have assembled a team with the appropriate expertise. The PI is a leading expert in the field of skin disorders with extensive experience in the use of gene therapy for the treatment of EB and has ample access to clinical samples. He/she has recruited experts in iPS cell technology and in the stem cell field. However, reviewers felt that the riskiest element of this proposal was not undertaken by the experts in that area, since the co-PI responsible for iPS cell technology is fairly junior and not highly experienced with regard to homologous recombination. Reviewers appreciated that the project manager was involved with the PI on the RDEB project for submitting an IND application. The leadership plan is clear and well designed. The proposal describes the roles and responsibilities of everyone involved and appropriate communication plans are included. The applicant institution provides an outstanding environment and is actively involved in supporting the project. All of the facilities including manufacturing are aligned with this project. The budget was considered high but likely important to achieve success at such a fast pace. However, reviewers thought that inclusion of the RDEB project was not justified and therefore recommended that it be excluded from the budget.
In conclusion, reviewers supported this high risk project as it is based on outstanding science and has the potential to critically advance the burgeoning iPS cell technology in a clinically justifiable setting.
A motion was made to move the application to tier 1, Recommended for Funding. The programmatic discussion focused on the high risk / high reward nature of this proposal, and panelists emphasized that this application would be unique in CIRM’s portfolio in that it advances an iPS cell-based therapeutic approach. Although a reviewer reiterated that each step required for the generation of the cell product has not yet been achieved, and even under the best of circumstances an IND filing would be expected to require much more than four years of research, many others felt that this application offers a unique opportunity to move iPS cell-based therapies closer to the clinic. Even if milestones cannot be reached, much will have been learned in this very exciting field, and even partial successes have the potential to transform the field and catapult iPS cell and gene replacement technology forward. Panelists further discussed the merits of advancing iPS cell therapies in DDEB in which large portions of the patient’s epidermis might have to be replaced, and wondered if metabolic disorders, which only require relatively small numbers of cells to provide therapeutic benefit, would be preferable. In favor of DDEB, a panelist pointed out that it is a debilitating orphan disease and as such may be amenable to fast track approval. While considering the readiness of this type of approach for clinical development, panelists pointed out that bone marrow transplants and mesenchymal stem cell transplants into hearts were advanced into the clinic when their supportive science was at a similar stage of maturity. Another reason in support of taking bold steps relates to the fact that immune rejection barriers exist for most stem cell-based therapeutic approaches under investigation, and therefore aggressively advancing iPS cell technology, which is largely expected to circumvent this problem, is justified. Potential safety issues will be discovered during the development stages of this project, so that the risk for the patients remains manageable. The motion to move the application to tier one passed.
- Andrew Balber