Stem cell therapies are entering a pivotal phase, with over 100 clinical trials underway to assess their potential in treating debilitating diseases such as Parkinson's, epilepsy, and diabetes. These trials represent a significant shift from unproven stem cell treatments, focusing on replacing or supplementing damaged tissues with lab-grown cells.
Parkinson's Disease: Replacing Damaged Neurons
For Parkinson's disease, the degeneration of dopamine-producing A9 neurons in the substantia nigra leads to motor symptoms. Current treatments using dopamine replacement drugs have limitations, including side effects and waning efficacy as the disease progresses. Replacing these degenerated cells with stem cell-derived neurons offers a potential long-term solution.
One such trial, co-led by neurologist Roger Barker at the University of Cambridge, involves transplanting A9 progenitor cells derived from human embryonic stem (ES) cells into patients' brains. A similar trial by BlueRock Therapeutics has reported preliminary results indicating safety and hints of efficacy, particularly at higher doses. Notably, these trials have not reported the uncontrolled movement side effects seen with traditional dopaminergic drugs or earlier fetal tissue transplants.
Barker notes that previous studies using fetal brain tissue transplants showed that the approach can work, sometimes transformatively, but a more reliable source material was needed. Stem cells offer a standardized and scalable source of specialized cells for transplantation.
Epilepsy: Restoring Neural Circuits
Beyond Parkinson's, stem cell therapies are also showing promise in treating epilepsy. A clinical trial by Neurona Therapeutics involves transplanting immature interneurons into the brains of individuals with drug-resistant epilepsy. The early results are striking: one year after the transplant, the frequency of severe seizures in the first two participants had dropped to almost zero, an effect that has been maintained for two years. Most other participants have also experienced pronounced reductions in seizure frequency, with no significant side effects or cognitive damage reported. The FDA has granted this therapy fast-track status.
Arnold Kriegstein at the University of California, San Francisco, a co-founder of Neurona Therapeutics, emphasizes the robustness of the treatment, noting that the outcomes for patients were strikingly similar even though procedures were carried out at different sites around the country.
Type 1 Diabetes: Regenerating Islet Cells
In the realm of diabetes, Vertex Pharmaceuticals is conducting a trial using stem cell-derived islet cells to treat severe forms of type 1 diabetes. These islet cells, developed from a human ES cell line by Douglas Melton and his colleagues, are designed to replace the insulin-producing cells destroyed by the disease. According to the company, 9 of the 12 participants who received the full dose no longer need to inject insulin, and another two were able to reduce their dose.
Melton, who entered the field after his son was diagnosed with type 1 diabetes, expressed surprise and delight at the results, highlighting the potential for patients.
While challenges remain, including refining cell selection and minimizing the need for immunosuppressants, these clinical trials mark a significant advancement in stem cell therapies, potentially revolutionizing the treatment of several debilitating diseases.
