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In a groundbreaking move towards the future of medicine, stem cell therapies are rapidly moving from research labs into clinical trials, with potential treatments for conditions such as cancer, diabetes, Parkinson’s disease, and heart failure now within reach. These trials, though still small and primarily focused on safety, signal a turning point in the development of regenerative medicine.
Andrew Cassy, a former telecommunications researcher, was diagnosed with Parkinson’s disease in 2010, leading to early retirement. Inspired by a desire to understand his condition, which he saw as an engineering problem, Cassy volunteered for clinical trials. In October 2024, Cassy took part in a radical study in Lund, Sweden, where surgeons transplanted neurons derived from human embryonic stem (ES) cells into his brain in the hopes of replacing damaged tissue. This pioneering study is part of a larger global movement, with over 100 clinical trials currently underway exploring the use of stem cells to regenerate tissues in diseases such as diabetes, epilepsy, cancer, and more.
One of the most promising aspects of these clinical trials is their focus on replacing or supplementing tissues damaged by debilitating diseases. Unlike unapproved stem cell therapies offered by shady clinics, which often use cells that do not turn into functional tissue, these studies are based on well-established science and aim to create functional, transplantable tissue.
While challenges remain, such as determining the best type of cells for different conditions and finding ways to eliminate the need for immunosuppressants (which prevent the body from rejecting transplanted cells but increase the risk of infections), researchers are optimistic. The progress in stem cell therapies has been described as “remarkable” by experts like Martin Pera, a stem-cell specialist at the Jackson Laboratory in Bar Harbor, Maine. Pera notes that it has only been 26 years since scientists first learned to culture human stem cells in laboratory flasks, yet in that short time, we have seen tremendous advancements in the field.
Cassy’s own story reflects the exciting potential of these treatments. His Parkinson’s disease was initially marked by a tremor at age 44, which later progressed to debilitating motor symptoms due to the degeneration of dopamine-producing neurons. Traditional treatments, which involve replacing the missing dopamine with drugs, are effective but come with side effects, such as uncontrolled movements. In contrast, the transplantation of stem cells into the brain offers the potential for a more permanent solution by directly replacing the lost neurons.
The concept of replacing these degenerated cells has a long history, dating back to 1987 when the first transplant of fetal-derived neurons for Parkinson’s patients took place in Sweden. Although the results were mixed, with some patients showing little benefit or suffering debilitating side effects, others experienced remarkable improvements, no longer needing dopaminergic drugs. This history, while promising, also highlighted the need for a more reliable source of stem cells.
The breakthrough came with the development of human ES cells and induced pluripotent stem (iPS) cells, which can be reprogrammed from adult cells into a pluripotent state. These cells have made it possible to create specialized tissues with much more control, offering a cleaner, more reliable source of material for regenerative therapies. Today, scientists can generate large numbers of dopamine-producing neurons and other specialized cells with a purity high enough for clinical use.
The trial Cassy is involved in, co-led by neurologist Roger Barker at the University of Cambridge, uses A9 progenitor cells derived from human ES cells, which are showing promising early results in Parkinson’s treatment. Similarly, another trial led by BlueRock Therapeutics, a biotechnology firm, has demonstrated that higher doses of these cells in Parkinson’s patients have not only been safe but also showed early signs of efficacy.
Beyond Parkinson’s, stem cells are being explored for a variety of conditions. A world-first achievement was recently reported in the treatment of diabetes, where stem cells reversed the condition in a female patient. The therapy involved generating functional islet cells from human ES cells, which are capable of producing insulin. This breakthrough has sparked a wave of optimism in the fight against type 1 diabetes, with several other studies following suit.
While conditions like Parkinson’s and diabetes are advancing quickly, challenges remain for other organs, particularly the heart and kidneys, which are more complex and harder to repair with stem cells. Nonetheless, researchers are making progress, with trials underway to inject immature heart cells into patients with heart failure and efforts to generate kidney tissue using stem cells.
Perhaps one of the most exciting areas of research is the use of stem cells to treat cancer. Several trials are investigating the potential of T cells or natural killer cells derived from stem cells to target cancer, offering hope for more effective and affordable treatments. Early reports suggest that these therapies are safe, well-tolerated, and in some cases, remarkably effective, even achieving full remission in some participants.
Despite the progress, challenges remain. The use of stem cells in clinical settings raises ethical concerns, particularly with the use of human ES cells, which come from embryos. Many researchers, however, are turning to iPS cells to avoid these ethical issues, although iPS cells come with their own set of risks, such as the potential for cancerous mutations. Still, stem-cell biologists are working tirelessly to ensure that the risks are minimized, using advanced techniques like gene-editing to reduce the likelihood of rejection and to improve the compatibility of transplanted cells.
The future of stem cell therapies is filled with promise, though it will take time to fully realize their potential. Some treatments may become widely available within the next five to ten years, marking a new era in regenerative medicine. For patients like Andrew Cassy, the journey is just beginning, but the possibilities are transformative. As he says, “This is research, and we don’t know how things will turn out. But I walked into the operating area with full confidence and no qualms.”
As clinical trials continue to unfold, the hope is that stem cells will not only revolutionize the treatment of Parkinson’s, diabetes, and cancer, but could one day provide a solution for many other debilitating diseases. The road ahead is still long, but the promise of regenerative medicine is closer than ever before.
Nature 637, 18-20 (2025). DOI: https://doi.org/10.1038/d41586-024-04160-0
