Stem Cell Therapy for Spinal Cord Injury: What Japan’s Stemirac Decision Means

Picture a 24-year-old who dives into a shallow lake on a summer afternoon.

One second he is fine. The next, he cannot feel his legs. A week later a doctor explains what happened to his neck, and then says the hardest sentence in the room: there is no treatment that repairs a damaged spinal cord. Surgery can stabilize the spine. Rehab can help him use what still works. But the cord itself does not heal the way a broken bone does.

That sentence has been true for a long time. It is why every headline about stem cell therapy for spinal cord injury gets read, shared, and sent to families who are desperate for something new.

This month brought one of those headlines out of Japan. It is a real development. It also has fine print that most of the coverage skipped. Let's read it together.

Why Is Spinal Cord Injury So Hard to Treat?

The spinal cord is the cable between your brain and your body. When it is crushed or bruised, nerve fibers are cut, cells die, and the body forms scar tissue around the injury. That scar keeps things stable. It also blocks nerve fibers from growing back across the gap.

Doctors grade the damage with the ASIA Impairment Scale, or AIS:

• AIS A: complete injury. No movement or feeling below the injury, including the lowest part of the spinal cord.
• AIS B: feeling is partly preserved below the injury, but no movement.
• AIS C and D: some movement is preserved. In D, more of the key muscles below the injury can work against gravity.
• AIS E: normal.

One fact matters for everything below. Some people improve on their own in the first months after injury, especially those with incomplete injuries. Rehab helps too. So when a study reports that patients improved, the real question is always: improved compared to what?

What Is Stemirac, and What Did Japan Decide?

Stemirac is made by Nipro and was developed with Sapporo Medical University. Here is how it works in practice:

• Source: the patient's own bone marrow, collected soon after injury (the label aims for within 31 days).
• Process: the MSCs are grown in a lab for several weeks.
• Delivery: one IV drip of 50 to 200 million cells.
• Who it is for: traumatic spinal cord injury graded AIS A, B, or C. It is not for old, long-standing injuries.
• Price: about 15.2 million yen per dose under Japan's national health insurance.

Japan has a special pathway for regenerative products. If early data suggest a product is likely to work and is reasonably safe, it can get conditional, time-limited approval. The company then has to collect more data and come back. Stemirac got that conditional approval in December 2018, with a 7-year deadline. Nipro applied for full approval in November 2025.

On October 15, 2026, the expert panel that reviews regenerative products for Japan's Ministry of Health, Labour and Welfare signed off on full approval. Japanese media reported it is the first product to go from conditional to full approval under this system. Of the eight regenerative products that got conditional approval since 2015, two lapsed before getting there, according to the Yomiuri Shimbun.

The next day, Health Minister Ueno called it "very groundbreaking" at a press conference. He mentioned patients who regained the ability to walk with the product combined with rehab. Formal approval by the ministry usually follows a panel endorsement by about a month. As of October 26, it had not been announced.

What Evidence Was Stemirac Originally Approved On?

This is the part that drew criticism in 2018 and 2019, and it is fair to lay it out plainly.

The original approval rested on one study (STR01-03). It was run at one hospital, it was open-label, and it had no control group. Thirteen patients got the cells. According to Japan's drug regulator, the PMDA, 12 of the 13 improved by at least one AIS grade by about day 220, and 3 improved by two grades or more. No deaths or serious side effects were reported.

The PMDA itself noted the problem. Without a control group, you cannot rule out natural recovery and the effect of rehab. Scientists quoted in Nature in 2019 raised the same concern, and a 2026 perspective in The Spine Journal argued that early commercialization on uncontrolled evidence risks scientific rigor and public trust. That is why the post-marketing data mattered so much.

What Did the New Comparison Data Show?

After launch, Nipro ran a post-marketing comparison survey. It compared patients who got Stemirac with patients who did not. It was not randomized and not blinded. 206 treated and 263 untreated patients enrolled. The main analysis included 73 treated and 66 untreated patients. Neurological grade was measured at 6 to 8 weeks after injury and again 6 months later.

• Complete injuries (AIS A): 42.1% of treated patients (8 of 19) improved by two or more grades, vs 3.8% (1 of 26) of untreated patients (p = 0.002).
• Incomplete injuries (AIS B or C): 59.3% of treated patients (32 of 54) improved by one or more grades, vs 25.0% (10 of 40) of untreated patients (p < 0.001).
• Safety: the panel saw no new safety concerns in about seven years on the market. Blood clots in the lungs are a listed risk with IV cell products like this.

So here is a fair summary. Japan's regulators looked at seven years of real-world data and decided the benefit is real enough to grant full approval. Some experts still question whether a non-randomized comparison with unequal rehab can prove that. Both things are true at the same time. A randomized, controlled trial would settle it. One has not been done.

What About iPS Cells for Spinal Cord Injury?

In July 2026, Keio University published the first human trial of cells made from induced pluripotent stem (iPS) cells for spinal cord injury, in Nature Medicine. iPS cells are adult cells reprogrammed in a lab into an embryo-like state, then turned into the cell type you want. Here, that was neural stem and progenitor cells, the early cells that become nerve tissue. We covered Japan's broader iPS program in Japan's iPS cell therapy approvals.

• Who: four men aged 26 to 66 with complete (AIS A) neck injuries at the C4 to C6 level, treated 14 to 28 days after injury.
• What: 2 million cells injected directly into the injured part of the cord, plus an immune-suppressing drug for about six months.
• Main goal, safety: met. No tumors and no side effects tied to the graft over 2 to 4 years of follow-up. There was one serious adverse event (a brief high potassium reading, likely a lab sample issue) and two related to the surgery.
• Exploratory signals: two of the four moved up to AIS C or D. In a comparison registry of 52 similar patients, about 12% to 15% did.

The authors were direct about the limits. Four patients. No control group. They wrote that the changes "cannot be attributed to the intervention." This was a safety study, and it did its job. Whether the cells help is a question for the next, larger trial.

What About MSC Trials in the U.S.?

At Mayo Clinic, the CELLTOP Phase 1 trial gave 10 patients with AIS A or B injuries a single dose of 100 million of their own fat-derived MSCs, injected into the spinal fluid through a lower-back puncture. Results were published in Nature Communications in 2024. There were no serious side effects. Headache and muscle or joint pain were the most common complaints. Seven of the 10 improved by at least one AIS grade by final follow-up, and three did not change. There was no control group.

A Phase 2 randomized crossover trial (NCT04520373, about 40 participants) is underway. Results have not been published.

Another long-running U.S. program uses cells made from embryonic stem cells (oligodendrocyte progenitor cells, from Lineage Cell Therapeutics). In a 25-person dose study published in 2022, there were 29 serious adverse events in total, two of them judged related to the procedure or the immune-suppressing drug, and no enlarging masses on MRI. Neurological recovery was measured, but again with no control group.

What Are the Honest Objections?

If you or someone you love has a spinal cord injury, you deserve the downsides as clearly as the upside. Here they are:

• No randomized proof yet. None of the studies above is a completed randomized, blinded trial showing the cells beat a fair comparison.
• Timing is narrow. Stemirac, the Keio cells, and the embryonic-derived cells were all given in the first weeks after injury. These results say nothing about injuries that are years old.
• Rehab is doing real work. In every study, patients also got rehab. Separating the two is the hardest part of this research.
• Procedures carry risk. Injecting into the spinal cord requires surgery. IV cell products carry a listed risk of blood clots. Immune-suppressing drugs carry infection risk. See our overview of stem cell therapy side effects.
• Approval is product-specific and country-specific. A decision in Japan does not make anything approved in the U.S. No stem cell therapy is FDA-approved for spinal cord injury. For how the FDA process works, see stem cell therapy and FDA approval and our post on Ryoncil, the first FDA-approved MSC therapy.

Does This Research Apply to Other Stem Cell Products?

No. And this is the part most marketing skips.

Trial results belong to the exact product that was tested. Stemirac is made from the patient's own bone marrow, grown under a specific process, and given at a specific dose within weeks of injury. The Keio cells are a different cell type entirely, placed directly in the cord by a surgeon. Change the source, the maker, the dose, the route, or the timing, and you have a different product. Its effects have to be studied on their own.

So if anyone tells you "Japan approved stem cells for spinal cord injury" to sell you something else, ask which cells, made by whom, and in what study.

Where The Stem Cell Club Fits

Plain answer: we do not offer Stemirac, iPS cell products, or any spinal cord procedure. We are not part of these trials and have no connection to the companies or universities running them.

We offer umbilical cord Wharton's Jelly MSC options sourced from an FDA-registered U.S. lab. That is a different cell source, made by a different lab, given differently than the products above. Lab registration covers facility and manufacturing standards. It is not FDA approval of a therapy. Our offerings are not FDA-approved to diagnose, treat, cure, or prevent any disease, and we do not offer them as a treatment for spinal cord injury.

If you are dealing with a spinal cord injury, your best team is a spinal cord injury specialist, a physical medicine and rehabilitation doctor, and a good rehab program. If you want to look into research, search ClinicalTrials.gov for "spinal cord injury" and bring what you find to that team. Trials often have strict timing windows, so ask early.

Questions to Ask Before You Believe Any "Stem Cells for Spinal Cord Injury" Claim

• Was there a control group? Natural recovery and rehab can both move AIS grades.
• When after injury were the cells given? Results from the first weeks do not apply to chronic injuries.
• How many patients got that exact product? Four, ten, or thirteen people is a start, not a verdict.
• Did everyone get the same rehab? If not, the comparison is weaker.
• Is it the same product? Results from one maker's cells do not transfer to another's.
• Who regulates it, and where? Ask for the trial number or the approval document.

We keep a longer checklist here: questions to ask any stem cell clinic.

Frequently Asked Questions