A major problem in regenerative medicine today is that stem cells have the ability to cause tumors and in most cases we currently lack methods to make them safe. For example, two of the most promising stem cells for regenerative medicine, human embryonic stem cells (hESC) and induced pluripotent stem cells (iPS), both readily cause tumors in mice and there is every reason to believe they will do so in humans. The reality is that if we cannot prove that stem cells are safe and do not cause tumors, they will never be used in patients. However surprisingly there is inadequate research into this fundamental problem and it is not funded to a significant degree by the NIH presenting a major gap in the field. In the proposed research we will address this problem by studying why hESC and iPS cells cause tumors and searching for new stem regulators that are safer. Our overall goal is produce safe hESC and iPS cell regenerative medicine therapies. One likely key culprit in the tumor forming capacity of these stem cells is a gene called Myc. Myc is a unique factor in the universe of stem cell regulators because it not only has key roles in the normal, positive functions of many stem cells, but also when found in excess it is one of the most potent cancer-causing genes in humans. Myc has also recently been found to be a critical factor driving iPS cells to form tumors. However, we cannot simply eliminate Myc since it is important for efficient generation of iPS cells and likely for the maintenance of the positive properties of stem cells, including hESC, needed for regenerative medicine. In order to achieve our goal to enhance the safety of stem cells without sacrificing our ability to efficiently generate them or their key functions, we will take two main approaches in the proposed research. The first is to study how Myc works in iPS cells and hESC in order to find methods to enlist the positive effects while eliminating the negative properties. Remarkably, there is currently no information on how Myc functions in iPS cells and hESC. The second is to screen in a global, unbiased manner for new stem cell factors that can substitute for Myc or enhance iPS function independent of Myc. When these studies are successfully completed we will for the first time know the factors responsible for inducing stem cells to cause cancer, paving the way for eliminating that function, and we will have discovered new stem cell regulators that have better profiles of safety and efficacy than existing factors such as Myc. Together these achievements will bring us much closer to using the vast potential of iPS and hESC for new therapies that are both safe and effective. Longer term our goal is to work with our neural (Alzheimer’s disease, Parkinson’s disease, and spinal cord injury), cardiac, and liver disease teams here to generate safe and effective stem cell based therapies tailored for each patient.
Enhancing the safety of regenerative medicine therapies will be of great benefit to the State of California both in terms of improving the lives of patients, by removing arguably the most serious roadblock to regenerative medicine, as well as enhancing the knowledge of the stem cell field. It will also further the development and clinical use of regenerative medicine leading to a new, valuable biotechnology. California should be a leader in developing safe, effective regenerative medicine.
This application is focused on elucidating mechanisms that control self-renewal and pluripotency and might at the same time contribute to the tumorigenic potential of pluripotent stem cells. An emphasis is placed on the role played by the Myc gene in the regulation of embryonic stem cell self-renewal and during reprogramming using the Yamanaka procedure for generating induced pluripotent stem (iPS) cells. Although Myc is not necessary for the formation of iPS cells, it appears to enhance reprogramming significantly. In the first aim, the principal investigator (PI) will assess the function of Myc in mouse and human embryonic stem cells (hESC) by down-regulating its expression. In the second aim she/he proposes to identify Myc targets in hESC and also study association of these targets with particular epigenetic modifications. The third aim proposes a functional screen to identify novel enhancers and suppressors of reprogramming of adult somatic cells by screening either a hESC cDNA library or a short hairpin RNA (shRNA) library.
Overall, this is a highly focused application, and the proposed studies have high significance for improving our understanding of basic stem cell biology and its clinical applicability. Reviewers expressed varying opinions regarding the proposed research plan but were uniformly enthusiastic about the applicant’s scientific leadership potential and the institutional commitment to him/her. One reviewer felt that given the broad interest in Myc as a reprogramming factor, studies related to Myc function are particularly timely, whereas another reviewer questioned the rationale for studying Myc in iPS cell formation when recent studies have suggested it is not required for that process. One reviewer expressed confidence that the intricate biological and molecular assays proposed should provide a substantial amount of data regarding the role of Myc in both self-renewal and pluripotency, whereas other reviewers pointed out that some of the proposed studies are not particularly innovative. One reviewer regarded the screens proposed in aim 3, although very ambitious, an interesting approach, whereas another reviewer questioned the feasibility of the screens based on experience in the field. Overall, feasibility of the project is supported by significant preliminary data both on the role of Myc in hESCs and the applicant’s ability to generate iPS cells using the Yamanaka method.
The applicant is already an internationally recognized expert in Myc biology. She/he has been an independent investigator for two years, and his/her track record as reflected in publications, grant funding, honors and scholarship predict a highly promising career trajectory. The career development plan is fairly generic in scope and aims, but it does provide defined milestones in terms of publications and grants. The applicant put together a very strong mentoring committee composed of four senior researchers with widely divergent expertise, all of whom are at his/her institution. In addition, she/he has identified several other individuals who will serve as consultants or co-investigators and will contribute to mentoring activities.
The environment for stem cell research at the home institution is exceptionally strong. Institutional commitment is presented in a fairly generic letter of support; research start-up funds and protected time for research are not specifically stated. Nevertheless, the institutional commitment to providing a rich collaborative environment through core facility access and numerous stem cell faculty is clearly evident. The applicant has been provided with a large amount of research space as well as dedicated cell culture and microscopy space.
Overall, reviewers were very enthusiastic about this applicant and his/her potential to become a leader in the field. They considered the institution to be a major asset for the investigator as well. Although the research proposal could have been stronger, reviewers agreed that the proposed studies will advance our understanding and contribute substantially to stem cell biology.