Background: Huntington’s disease (HD) is a genetically inherited, fatal neuropsychiatric disorder which strikes 1/10,000 people. The cause is a repeat expansion in the Huntingtin gene which leads to progressive brain degeneration, ultimately resulting in death after 15-20 years. HD passes from generation to generation. Each child of a parent with HD has a 50% chance of inheriting the HD mutation. There is currently no treatment, therapy or medication that will delay the onset of the disease or slow its progression. All currently available treatments are palliative, which focus on symptom management alone. There is currently no cure for HD.
Proposed therapy: We propose a novel therapy for HD: implantation of mesenchymal stem cells engineered to secrete Brain-Derived Neurotrophic Factor (MSC/BDNF). BDNF levels are reduced in the brains of HD patients. BDNF has been shown in numerous transgenic HD mouse studies to prevent cell death and to stimulate the growth and migration of new neurons in the brain, and is thus a lead candidate for neuroprotection in HD. We are using MSCs as delivery vehicles to produce BDNF in the affected areas of the striatum. We are conducting detailed tests of MSC/BDNF in HD mouse models in preparation for a proposed Phase I clinical trial of MSC/BDNF implantation into the brain of HD patients (HD-CELL), with the goal of slowing disease progression.
Progress, Year 2 of grant: Based on recommendations from the CIRM Clinical Development Advisory Panel (CDAP), we altered our vector and added a second animal model. Following CDAP, we repeated all manufacturing and testing of MSC/BDNF using the new vector, produced using Standard Operating Procedures (SOPs) from our UC Davis Good Manufacturing Practices (GMP) Facility. We have shown that MSC/BDNF produces high levels of BDNF and that a multiplicity of infection of ten virus particles per cell generates a single unrearranged integrant per cell, on average. This is data critical to the Recombinant DNA Advisory Committee (RAC), for whom we have prepared an Appendix M application. RAC approval is needed prior to FDA approval because it is a proposed stem cell gene therapy trial. We are currently refining our application to the FDA and will seek CIRM approval for submission.
We are completing our double-blinded studies, now using the new vector, examining the effects on disease progression of implantation of MSC/BDNF in two strains of HD transgenic mice: YAC 128 and R6/2 (CAG 120). The R6/2 (CAG 120) model has the early onset of neurologic dysfunction and dies much earlier than wild-type of YAC 128 models. For this reason it is a more suitable model of juvenile HD. In the R6/2 model we have successfully demonstrated that implantation of MSC/BDNF causes an improvement in deficits in open field exploration, a behavioral assay. We have also shown that MSC/BDNF causes increased neurogenesis in the brain of treated mice, an important milestone.
The YAC 128 model develops slowly progressive behavior symptoms in mid-life and has loss of brain cells that mirrors changes seen in HD patients. In the YAC 128 model we have shown that implantation of our MSC/BDNF product decreases striatal atrophy between 8 and 12 months of age. Wild type mice have a typical lifespan of two years, so this age in the YAC 128 mouse roughly corresponds to the typical age at onset for early-stage HD patients that we are proposing to treat in our future planned Phase 1 study, HD-CELL.
Clinical Update: In tandem with the on-going preIND studies in the lab, the clinical team is conducting an observational study, PRE-CELL. The goal of PRE-CELL is to establish baseline characteristics and track disease progression in a group of early stage HD patients. PRE-CELL subjects undergo detailed neurological, psychiatric, cognitive, imaging and laboratory testing, including measurement of BDNF levels. PRE-CELL participants who have completed at least 1 year of follow-up and meet inclusion and exclusion criteria will be considered for the future planned cell therapy trial. PRE-CELL has been approved by the Institutional Review Board at UC Davis since July 2013 and is still enrolling. For additional information, please go to: ClinicalTrials.gov Identifier: NCT01937923.
Significance: Our progress to date supports the completion of our final pre-clinical studies and our plan to go forward toward regulatory approval. There are potential applications of our research beyond HD. Our biological delivery system for BDNF sets the precedent for adult stem cell therapy in the brain and could potentially be modified for other neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), spinocerebellar ataxia (SCA), Alzheimer’s disease, and some forms of Parkinson’s disease. It also provides a platform for our future gene editing studies, since we will again use MSCs to deliver the needed molecules into the neurons.