Huntington's disease destroys the brain one decade at a time. Unlike most conditions covered in this newsletter, it is entirely predictable: if you carry the gene, you will develop the disease. If you develop it, there is nothing approved that changes its course. Families live with that fact for years before symptoms arrive. Last month, for the first time, a person with Huntington's disease had stem cells placed into their brain.
THE RADAR
An "immune reset" puts lupus patients into remission
Researchers at University College London reported this month that 5 of 9 patients with severe, treatment-resistant lupus achieved remission following a single infusion of CAR-T cell therapy in the Phase 1 CARLYSLE trial. Five of the first six at the lower dose responded, with average follow-up of 11 months and stabilisation or improvement in kidney function where it had been damaged. CAR-T uses the patient's own T cells, not stem cells — but the concept of reprogramming the immune system to stop attacking the body runs through every cell-based autoimmune therapy in development.
The epilepsy cell therapy heading for Phase 3
Neurona Therapeutics updated data from 31 patients across two Phase 1/2 trials of rezanecel, a stem cell-derived therapy for drug-resistant epilepsy, at the American Academy of Neurology meeting in April. The low-dose group continues to show 92% median seizure reduction, now confirmed at 18 to 24 months. The pivotal Phase 3 EPIC trial, randomised and sham-controlled, is enrolling its first patient in the second half of 2026. If the results hold, rezanecel would be the first stem cell-derived therapy to reach regulatory submission for a neurological disease outside blood and eye.
Patient One
Before the trial, the facts about Huntington's disease. It is caused by a mutation in the huntingtin gene, which leads to the gradual destruction of neurons in the striatum, a brain structure central to movement and cognition. Symptoms typically begin in the mid-thirties to fifties. They worsen over ten to twenty years: uncontrolled movements, progressive cognitive decline, depression. The disease is fatal. Every person carrying the gene mutation will develop it. There are drugs that manage some symptoms. There is nothing approved that slows the underlying destruction.
On June 23, UCI Health announced the REGEN4HD trial, the world's first in-human clinical trial of embryonic stem cell-derived neural cells for Huntington's disease. The therapy, called hNSC-01, uses neural stem cells manufactured at the UC Davis GMP facility and delivered by a six-hour surgical procedure inside an MRI suite. The cells are placed directly into the striatum, guided by robotic mapping technology designed for precision at the scale of millimetres. The trial is funded by a $12 million California Institute for Regenerative Medicine grant and led by Dr. Leslie Thompson, who has studied Huntington's disease at UC Irvine for more than three decades.
The first patient was treated in May. Dr. Ravi Rajmohan, the trial's principal investigator, reported no serious adverse events. A second patient is scheduled for July. The trial will enrol 21 people aged 18 to 65 with early-stage HD.
Animal studies suggest hNSC-01 can protect surviving neurons from further loss, replace neurons that have been destroyed, rebuild damaged circuits, release BDNF (a protein critical to neuron survival that is depleted in HD patients), and clear the toxic protein aggregates that drive the disease. That is the preclinical picture. In one human patient, safely, the cells have been placed. Whether they are doing any of those things in a human brain is not yet known.
This is Phase 1b/2a. The current goal is safety, not efficacy. One patient's tolerance of the surgical procedure is not a result. It is the beginning of a process that will take years before anyone can say whether hNSC-01 changes what Huntington's disease does to the people who have it.
What matters is that a line has been crossed. For a disease with no approved treatment that modifies its course, a first-in-human trial is not a small thing. It is simply also not a cure.
Primary source: UCI Health / EurekAlert, June 23, 2026. Trial: REGEN4HD (Phase 1b/2a), funded by CIRM.
STUDY OF THE WEEK
Scientists set out to find stem cells. They found something else instead.
Published in Science (June 12, 2026) | Aged mice and ex vivo human tissue | Stanford Medicine
What they did: Researchers led by Helen Blau, director of the Baxter Laboratory for Stem Cell Biology at Stanford, tested whether blocking a protein called 15-PGDH could restore cartilage in aging and injured joints. 15-PGDH is a gerozyme, a class of proteins that increases with age and suppresses the body's ability to repair itself.
What they found: A single injection fully reversed cartilage loss in aged mice and prevented arthritis from developing in half of post-injury cases. Human cartilage samples from knee replacement patients began producing new cartilage when exposed to the inhibitor in the laboratory. No existing FDA-approved drug can reverse cartilage loss.
Evidence level: Aged mice, with ex vivo human tissue validation. No human clinical trial yet.
The counterintuitive finding: The regeneration did not involve stem cells. Blau herself noted: "We were looking for stem cells, but they are clearly not involved." Instead, existing cartilage cells called chondrocytes appear to reprogram their gene activity toward a younger, more functional state. Regeneration through reprogramming, not replacement.
Why it matters anyway: An oral version of the 15-PGDH inhibitor is already in clinical trials for age-related muscle weakness. The team expects a human cartilage trial to follow.
WHAT'S REAL / WHAT'S NOISE / WHAT TO WATCH
REAL
Neurological disease is now within the realistic scope of stem cell therapy. Rezanecel's Phase 1/2 data in drug-resistant epilepsy, 92% median seizure reduction sustained at 18 to 24 months, represent the strongest human signal to date for a stem cell-derived therapy in a brain disorder. That a randomised Phase 3 trial is now recruiting marks the transition from early signal to rigorous test.
NOISE
The phrase "world's first" as a claim from a clinic or wellness provider. REGEN4HD is genuinely the first in-human embryonic stem cell trial for Huntington's disease. That same language in commercial settings, applied to any condition without a regulatory IND, a peer-reviewed protocol, and independent oversight, is marketing. The distance between those two uses of the phrase is the distance between medicine and sales.
WATCH
The CARLYSLE trial's expansion beyond lupus. If the immune reset effect from CAR-T holds across autoimmune diseases, including early signals in multiple sclerosis, the same reprogramming principle applies to conditions where stem cell-derived therapies are also in development. Those two fields are moving toward the same territory.
THE RED FLAG REPORT
The Comparison Problem
REGEN4HD will be cited. Clinics offering stem cell infusions for neurological conditions will reference "trials like the one at UC Irvine" in the weeks ahead.
The hNSC-01 cells were manufactured in a licensed GMP facility, delivered under an FDA-approved IND, by a specialist neurosurgical team, during a six-hour intra-operative MRI procedure targeting a specific brain structure. That is not comparable to an outpatient infusion of uncharacterised cells.
One question cuts through the comparison: is the therapy being offered administered under an IND filed with the FDA? If not, the analogy ends there.
READER LENS
Phase 1 versus Phase 1b/2a: what the labels actually mean
A Phase 1 trial is primarily a safety study. The central question is whether a therapy can be given without causing serious harm. Efficacy is not the objective.
Phase 1b/2a, as in REGEN4HD, is a hybrid. The 1b portion escalates doses across small patient groups to identify a safe range. The 2a portion begins looking for early signals of whether the therapy is doing anything in the disease, though these are exploratory and not designed to prove the treatment works.
One patient treated with no serious adverse events means the trial can continue. It does not mean the therapy works. Every Phase 1 report in this newsletter carries that same caveat.
For people who carry the Huntington's gene, the diagnosis can arrive decades before the symptoms. The wait is its own condition. What a Phase 1 trial opening means to those families is different from what it means in a press release. The wait now has something new in it. That is not nothing, and it is not enough.
