Webinar Q and A follow-up: ‘Gene-modified mesenchymal stem cells as a potential treatment for Huntington’s disease: preparing for a planned Phase I clinical trial’

Follow-up of the live webinar Q and A session

Thank you everyone who attended the live webinar ‘Gene-modified mesenchymal stem cells as a potential treatment for Huntington’s disease: preparing for a planned Phase I clinical trial’. Below are the responses to the questions posed during the live event that we did not have time to answer. We hope this is a useful resource and thank our attendees and our speakers, Jan Nolta, Vicki Wheelock and Kyle Fink (UC Davis, CA, USA), for their time.

How significant is the finding that the engineered stem cells reduce anxiety in the HD mouse model?

We feel that this is a critical piece of data as one of the most debilitating aspects of the disease, as reported by the patients, are the emotional and cognitive disturbances that accompany the progressive worsening of symptoms.

Can you explain how increased neurogenesis might help in HD?

The brain is an amazing organ in that following disease, injury, or insult it will activate mechanisms to try and repair itself. What is becoming more evident in Huntington’s disease is that this inherent repair mechanism is impaired. Our studies and others provide evidence that engineered MSCs not only increase endogenous neurogenesis, but likely the release of BDNF helps in the chemotaxis and maturation of new functional neurons.

How long will it be before techniques like gene editing might be ready to test in patients?

This field is a few years behind cell transplantation, but is rapidly catching up with the discovery of new gene editing techniques. Roche pharmaceuticals partnered with ISIS is proposing a trial using antisense oligonucleotides that will be tested in Europe and Canada in the near future.

Can you address release testing for MSCs for the Phase 1 trial?

Our cells undergo rigorous quality control and release testing in our Good Manufacturing Practice facility and we are in contact with the FDA to validate the Standard Operating Procedures that we have defined for the proposed Phase 1 trial.

How are the number of copies of lentivirus calculated to ensure <2 copies of lentivirus per cell is met, according to the FDA?

We initially calculate the “MOI” or multiplicity of infection needed to achieve that level of integration (number of virus particles added per target cell) and then we follow a Standard Operating Procedure established in our lab using real-time PCR to determine copy number.

Did the MSCs survive well?

Yes. It does not appear that the MSCs are rejected by the host immune system or that they undergo apoptosis (programmed cell death) following transplantation. However, it appears that these cells do not permanently engraft into the host cytoarchitecture, but are there for a couple of months. We actually feel that this is a strength of the MSC for a trial aimed at safety as these cells are able to promote functional recovery, prevent striatal atrophy and then clear from the system when they are no longer needed.

In neurogenesis and behavioral studies, it seems MSCs only (no BDNF) resulted in a significant positive effect, sometimes better than BDNF. Is engineering BDNF even needed?

This is an excellent observation. Our lab actually has a review paper in press with RegMed that should be available soon chronicling the use of non-engineered MSC to treat animal models of Huntington’s disease. There is extensive positive data. We feel that the cells by themselves offer excellent potential to treat HD, however we feel that it is necessary to give the cells an extra boost of the main trophic factor needed in HD, due to amelioration of the behavioral deficits, the reduction in striatal atrophy, and the lifespan improvement that we obtained using MSC/BDNF. Since our cells are not selected for only those making the extra BDNF, the planned therapeutic is actually a mixture of MSC and MSC/BDNF. Approximately half of them are transduced by the vector, using our SOPs.

What medium was used to grow the MSC in vitro prior to injection? Was it serum-based?

We are in the process of preparing a manuscript describing all of the culture techniquesused prior to transplantation and it will hopefully be accepted and available soon.

What was the survival rate of the MSCs after transplantation? And were there any ectopic effects observed?

We have never observed any ectopic formation following transplantation of engineered MSC in any of the disease models used in our lab, including the current studies where they were injected into the striata of many HD mice. As mentioned above, we are preparing a manuscript that will contain detailed information on cell retention in the brains of our transgenic mouse models.

What is the upper limit of expansion (population doubling limit) for the gene modified MSCs so that they still maintain the desired potency? This will have implications for the scalability of the manufacturing process.

Our Good Manufacturing Practice facility is in contact with the FDA to determine the ideal conditions for scaling this product for clinical use. Our lab is currently preparing another manuscript describing the culture conditions and potency assays used for our engineered MSC trials.

When do you foresee FDA approval for the HD-CELL?

As Dr. Nolta has mentioned we have submitted our PreIND package to the FDA and will be working through the approval process in the coming months.

Please describe dose selection and justification for first doses in HD patients.

The dose selection was based on evidence of potency from our pre-clinical studies, however, we are awaiting FDA guidance on this issue during our PreIND meeting.

Why do the untx MSCs do as well or better than the BDNF ones in mouse studies? Also, did you correlate MSC engraftment with the effects noted?

We chose MSC as our delivery platform for a variety of reasons including their strong safety profile and ability to be engineered to produce neurotrophic factors. However, the main reason we have chosen MSC as the cell delivery platform is the rich history of MSCs alone to provide functional recovery following transplantation in animal models of neurodegenerative diseases. As mentioned above we have a review paper in press with RegMed that details the potential of MSCs for HD.

We do feel that it is necessary to give the cells an extra boost of the main trophic factor needed in HD, due to better performance of MSC/BDNF in amelioration of the behavioral deficits in open field, the reduction in striatal atrophy, and the lifespan improvement.Since our cells are not selected for only those making the extra BDNF, the planned therapeutic is actually a mixture of MSC and MSC/BDNF. Approximately half of them are transduced by the vector, using our SOPs.

How long do you expect the MSC-HD to remain in HD patients: days, weeks, months or years?

First for clarification the MSC used in this proposed trial will not be from an HD patient and will not have the gene mutation. They are from unaffected and pre-screened donors. Our pre-clinical evidence suggests that the majority of the cells will be cleared from the brain after several months, however it is possible that a small population of cells will remain longer in the human brain prior to being cleared.

What is the timing of MSC Tx in HD patients versus the previously Txed mice? Will earlier treatment ‘blunt’ the striatal atrophy if Tx is earlier?

This is an excellent question and a very interesting topic for our lab. Currently, for the planned HD-CELL trial we will be transplanting the cells into early-stage HD patients (TFC between 10 and 13) and have tried to recapitulate this same disease progression in our mouse models.

Why do MSCs alone decrease striatal atrophy? What is the MTD? Repeat injections? What is the anticipated dosing of the patients?

As mentioned above there is a rich history of MSCs alone providing functional and anatomical recovery in animal models of HD. We believe that the mechanism of action is through providing a more suitable microenvironment for the medium spiny neurons in the striatum through immune-modulation and reduction of oxidative stress. However, the main mechanism is believed to be neuroprotection and increased neurogenesis provided by an increase in BDNF. In our studies the MSC/BDNF reduced the levels of striatal atrophy to a larger extent than the MSCs alone. We are in conversations with the FDA to establish a dose schedule for the patients that would be safe and provide beneficial effects.

These are autologous MSCs. Do you think treatment could be more rapid using previously engineered allo MSCs and might result in improved results?

These will be allogenic MSC isolated from a healthy donor and expanded in our Good Manufacturing Practice facility. All pre-clinical mouse studies were performed with healthy donor MSC.

View the webinar on demand here, and the Q&A transcription here.