Resident tissue stem cells divide and multiply when a tissue is injured. Stress, disease and aging diminish this capacity of adult stem cells. The applicant aims to promote endogenous adult stem cell self-renewal and proliferation and thereby stimulate tissue regeneration, circumventing the hurdles associated with introducing exogenous stem cells. The investigator has found that a specific secreted signaling factor regulates stem cell self-renewal and proliferation and has identified a strategy for localized in vivo delivery of this protein to sites of musculoskeletal injury. The applicant proposes to optimize formulation and activity of the protein, to optimize in vivo imaging systems to track it, and to employ models that mimic human bone grafting, fracture healing, osteoporosis, and muscle trauma to demonstrate the efficacy of the approach.
The idea to stimulate resident stem cells to achieve tissue regeneration of musculoskeletal structures is of considerable significance, since it avoids issues related to immune responses to allogeneic tissues. Similarly, the concept of a device-drug combination proposed in this application has merit, since it will meet less FDA regulatory hurdles than cell-based therapies, although the delivery component of the proposed approach may complicate this strategy to achieve a lower regulatory threshold.
Enthusiasm for this proposal was strongly dampened, especially during the discussion at the review meeting, due to major concerns about the rationale and maturity of the concept. Critical information cited in the application to support the maturity of the concept is currently under review and was not available to the reviewers. To one reviewer it was unclear how the injection of a protein that promotes self renewal and proliferation could be expected to lead to the ordered development of normal tissue in situ. Furthermore, the potential to promote tumor development using this scheme is not discussed in the application. Based on the fact that the protein is known to target many different cell types, another reviewer voiced concern about the possible side effects of this factor on other organs. It was also not clear how the proposed program will move to clinical trials. Given the critical role of the protein in this approach, good manufacturing practice (GMP)-compliant production of this protein should be considered as early as possible to support the clinical trials which are the required endpoint of the subsequent Disease Team Research Award. Furthermore, the applicant did not identify a specific disease target, but instead proposed to demonstrate the efficacy of the approach in multiple tissue models which makes this project highly unfocused and overly ambitious. Finally, in addition to mobilizing resident stem cells, the applicant also proposed the later use of human embryonic stem cells and induced pluripotent stem cells, but it remains unclear how s/he will determine which approach to pursue.
The principal investigator (PI) is a surgeon with a strong track record of translating basic and preclinical findings into clinical studies, and with a long history of leadership. S/he currently leads a large program at his/her home institution. The PI has earned an MBA and has experience in the commercialization of scientific ideas as scientific founder of two start-up companies funded by venture capital firms. Thus, the PI should be readily able to carry out the planning process and is well qualified to lead this team.
The applicant has already assembled a strong team of local faculty in areas critically important for the success of this project. The planning strategy will be appropriately driven by the definition of milestones along a five year roadmap to clinical trials, and each team member has input as defined by their respective expertise.
Resident tissue stem cells divide and multiply when a tissue is injured. Stress, disease and aging diminish this capacity of adult stem cells. The investigators aim to promote adult stem cell self-renewal and proliferation and thereby stimulate tissue regeneration, circumventing the hurdles associated with giving exogenous stem cells. They have found that Wnt3a regulates stem cell self-renewal and proliferation and have a strategy for localized in vivo delivery of Wnt3a to skeletal injury sites. They will generate purified Wnt proteins, package them, optimize the formulation and regulate activity through selective heating. They will build scaffolds for slow release of Wnt nanovesicles and optimize in vivo imaging systems to track them. They will employ models that mimic human bone grafting, fracture healing, osteoporosis, and muscle trauma. The award will be used to identify opportunities and determine the feasibility of and the extent to which this approach is scaleable and transferable.
Reviewer One Comments
The concept of using stem cells present in situ to achieve tissue regeneration of musculoskeletal structures is of considerable significance, given the wide prevalence and high health care costs of musculoskeletal injury. The concept avoids ethical issues and issues related to immune responses to allogeneic tissues. The maturity of the concept is somewhat difficult to assess, as the data supporting it is not available to the reviewer. The demonstration that the biological activity of Wnt3a is enhanced by packaging the protein into lipid nanovesicles is under review and the data are not presented in the application. The demonstration that liposomal Wnt3a accelerates regeneration of bone by 350 percent is also under review and not accessible to the reviewer. Several issues are therefore left open with respect to the efficacy of this approach. It is unclear how the injection of a protein that promotes self renewal and proliferation could be expected to lead to the ordered development of normal tissue in situ. Furthermore, the potential to promote tumor development using this scheme is not discussed. Thus, there are concerns about the rationale and maturity of the concept.
Dr. Longaker is the Deane P. and Louise Mitchell Professor of Surgery, Director of the Program in Regenerative Medicine, and Deputy Director of the Institute for Stem Cell Biology and Regenerative Medicine at Stanford University. This program involves greater than 150 affiliated faculty, demonstrating Dr. Longaker’s leadership experience. Dr. Longaker is a physician-scientist who is trained in craniofacial surgery and has a substantial track record for his research in craniofacial development, bone repair, skeletal tissue engineering, adipose-derived mesenchymal stromal cells, and wound repair. He has published more than 850 papers and lists nine of these that are in high profile journals. Dr. Longaker served as PI on the Stanford Clinical Translational Science Award planning grant which was funded by the NIH in 2006. He completed the UC Berkeley-Columbia University MBA III program in 2003 and has experience in the commercialization of scientific ideas as scientific founder of two start-up companies funded by venture capital firms. Thus, the principal investigator has a strong track record of translating basic and preclinical findings into clinical studies in the field and has strong leadership experience. He should readily be able to carry out the planning process.
The investigator has already assembled a strong team of faculty in critically important areas for the success of this project. These include specialists in skeletal regeneration and repair, Wnt biology, molecular imaging, muscle stem cells, embryonic stem cells, biomimetic materials, adult stem cells, protein engineering, biostatistics, medical devices and musculoskeletal disease. The inclusion of all of these team members strengthens the likelihood that the investigators will succeed in achieving their goals. The planning strategy will include a strategy session to delineate the clinical problems, to address and establish timetables and a rough budget. Milestones will be defined and all team members will be included in the planning process based on their respective expertise. The planning process appears to be well-thought out. The team will be well-prepared to compete for subsequent disease team research awards.
Reviewer Two Comments
- Concept: The concept is to develop a biomimetic approach based on stimulating, expanding and differentiating endogenous adult stem cells to regenerate musculoskeletal tissue.
- Evidence and maturity: This concept evolves from the ability of Wnt3a protein to promote self-renewal and proliferation in lipid vesicles, therefore yielding 350% bone regeneration. If successful, this will be a simple approach for regeneration of musculoskeletal tissue. This is a biochemical approach. If the in vivo regeneration can be attributed to local tissue stem cell expansion and differentiation (these results are in review), there will be a strong justification for CIRM funding.
- The device-drug combination product approach will meet less FDA regulatory hurdles. However, the delivery scaffold component may complicate this. The composition and roles of such a scaffold and how nanovesicles are incorporated into the scaffold remain to be defined.
- The PI also discussed the use of hESCs and iPS cells as other approaches the team will embark on. What will be the specific aims and rationales for these approaches? When will the team begin to work on these approaches?
The maturity of this approach remains to be demonstrated.
- Significance: The proposed concept addresses an important unmet clinical need in treating musculoskeletal impairments.
The PI has been directing a multi-investigator program on regenerative medicine; is an expert in musculoskeletal repair and regeneration and wound healing; has experience in leading translational research. He is well suited to assemble and lead an outstanding team.
- The PI proposed to demonstrate the efficacy of the biomimetic approach in multiple tissue models including osteogenic, chondrogenic, musculogenic models. This, combining with the undefined effort on adult stem cells, hESCs and iPS cells, makes this project highly unfocused and overly ambitious.
- Given the critical role of Wnt3a in this approach, GMP production of this protein should be considered as early as possible to support the clinical trials at the end of the “Disease Team Award”.
Reviewer Three Comments
Concept to stimulate endogenous regeneration of musculoskeletal damage is sound. Concept of device-drug has strong merit.
Feasibility of use of liposome-packaged Wnt3a cannot be evaluated since the key publications by Morrell et al and Leucht et al are still in review.
What about possible side effects of Wnt administration on other Wnt-responsive organs such as the bone marrow, gut and skin?
The PI Dr Longaker has an excellent track record and is ideally positioned based on his training and experience to lead the disease team.
The planning strategy focuses mainly on recruiting expertise from the faculty at Stanford. This is indeed a rich academic environment but the PI acknowledges the need to recruit additional collaborations in the area of cartilage regeneration.
The planning is appropriately driven by the definition of milestones along a five year roadmap to clinical trials. Each team member has input as defined by their respective expertise. This is a good model that is likely to yield the desired organizational structure and outcome.