Pre-clinical assessment of pluripotent stem cell therapy for Huntington’s disease – HD-SCT

First we derived (or imported), quality controlled and banked one Macaca fasicularis iPSC line and one GMP-compatible human embryonic stem cell line required for the HD-SCT program. Second we developed a research grade protocol for the production of striatal cells relevant to HD cell therapy investigating in particular the roles of Wnt and Hedgehog pathways on telencephalic specification and dorso-ventral patterning in hPSC derivatives. Third we adapted this protocol in order 1) to allow its use with monkey iPSC to produce allogenic cell therapy product for experiments in HD monkey and 2) to enhance the overall GMP compliance of the differentiation protocol. Fourth, we generated a new primate model of HD based on excitotoxic lesions creating both motor and cognitive deficits. Once the model was carefully validated, we proceeded to test the therapeutic efficacy of allografting macaque- iPSC striatal derivatives.

HD-SCT has enabled us to: 1) address the question of the production from human PSC of cell therapy product relevant to HD patient, 2) validate a new model of Huntington's disease with cognitive deficits in non-human primates; 3) evaluate the sensitivity of our follow-up methodology to detect the functional impact of the transplanted cells in this model; and 4) identify essential immunological issues that arise even in the allograft context and that need to be carefully and systematically investigated in pre-clinical animal models as well as HD patients.

The translational research work on HD stem cell therapy within the HD-SCT program has paved the way for the setup of a multi-center joint effort aimed at tackling the huge complexity of taking stem cell therapy to clinical application for Huntington's disease. This effort is coordinated by a FP7 European consortium named “Repair-HD” that combines all elements required to drive this technology to the point of clinical delivery.

Nicoleau et al Stem Cells. 2013 Sep;31(9):1763-74.
Perrier AL & Peschanski M Cell Stem Cell. 2012 Aug 3;11(2):153-61.
Viegas P et al Prog Brain Res. 2012;200:373-404.
Perrier AL & Anne-Catherine Bachoud-L

Huntington's disease (HD) is a devastating monogenic disease. There is no known treatment for this pathology whose symptoms include progressive motor, psychiatric and cognitive dysfunctions, associated with a massive degeneration of the striatal medium size spiny GABA neurons. Most of HD patients die within 15-18 years after the onset of symptoms. Recent clinical findings have shown that HD would partially respond to treatment by substitutive cell therapy using grafts of fetal origin. However, this grafting technique is limited by logistic and ethical problems that restrict considerably the number of patients that may benefit from it. Potent alternative sources of cells that would be easily accessible to surgeons are therefore urgently needed. Finding such cells is a crucial step towards the development and validation of an efficient clinical application in patients. Because of their extended differentiation potential and their unlimited capacity to self-renew, human pluripotent stem cells are in theory the best candidate cells to be grafted. In fact, we have recently demonstrated that human and monkey embryonic stem cell differentiation can be directed towards striatal neurons both in vitro and in vivo after transplantation in HD rats. This suggests a possible therapeutic potential of hESC for HD. However, a thourough pre-clinical assessment of such pluripotent stem cell-derived grafts is required to ascertain the applicability of this therapeutic strategy in HD patients.
The goal of the HD-SCT (HD-Stem Cell Therapy) proposal is to build on recent achievements in stem cell biology and clinical trials using fetal neural cells in HD patients to evaluate the therapeutic potential of pluripotent stem cells in a pre-clinical setup (allograft) and to develop the protocols needed for the establishment of banks of clinical-grade, ready-to-use, and safe batch striatal progenitor cells.
Fetal graft therapy currently used in HD clinical trials across Europe has greatly benefitted from the results obtained using primate models of HD. Since human striatal grafts mature too slowly to be appropriately assessed in rats, allografts in HD monkeys was the model of choice. Moreover, motor and cognitive behavioral tests are more relevant in primate models than in rodents. In addition, allografting better mimics “clinical transplantation” scenario with regard to immune response of the host to the graft. Accordingly, the first aim of HD-SCT is to assess the therapeutic potential of striatal cells derived from monkey-ESs and iPSCs in a monkey model of HD. Neuro-imaging will be used to monitor graft survival and cell maturation and the potential correction of cortical hypometabolism through striatal repopulation. Behavioral tests aimed at quantifying motor and cognitive deficits reminiscent HD pathology will be used to measure the potential benefit associated with stem cell transplantation. Current differentiation protocols that rely on mouse feeder cells or serum containing media are not compatible with future clinical application. Consequently, HD-SCT’s second aim is to adapt current research-grade differentiation protocols to clinical-grade standard and address the issue of the banking of stem cell derived striatal graft. Furthermore, HD-SCT will address the issue of the generation of safe transgenic pluripotent stem cell lines. Accordingly, HD-SCT’s third aim is to test “meganuclease-driven homologous recombination” technology as a way to produce safer transgenic pluripotent stem cell lines for human use.
HD-SCT expected impact is ultimately to accelerate the development of clinical applications of human pluripotent stem cells for the treatment of Huntington’s disease. To achieve this, HD-SCT relies on a small consortium of three experienced partners in the field of stem cell biology and its pre-clinical/ clinical application, with balanced and complementary skills highly relevant to the subject of the proposal.