How stem cell therapy works, and what the research shows

Last reviewed: October 2026

"Stem cell therapy" covers a lot of different things. Some are well established. Most are still being studied. This page is the short, sourced version: what these products are, how scientists think they work, what the best studies have found so far, and where to read more.

First, which "stem cells"?

Blood-forming stem cells (hematopoietic stem cells) come from bone marrow, blood, or umbilical cord blood. Bone marrow transplantation is the original stem cell success story: E. Donnall Thomas shared the 1990 Nobel Prize for it [1]. Today the only stem cell products the FDA lists as approved in the U.S. that come from cord blood are blood-forming cells for disorders of the blood system [2].

Mesenchymal stromal cells (MSCs) are a different cell type. Researchers first grew them from bone marrow in 1970 [3], and the name "mesenchymal stem cells" was popularized in 1991 [4]. MSCs can be grown from bone marrow, fat, and umbilical cord tissue, including the jelly-like tissue called Wharton's jelly [5]. Most of what clinics call "stem cell therapy" for joints, backs, and nerves refers to MSCs or tissue preparations said to contain them.

Related products that often get grouped in: PRP (platelet-rich plasma, made from your own blood, with no stem cells), and exosomes (tiny cell-released packets, with no living cells).

How MSCs are thought to work

The early idea was that injected MSCs would turn into new cartilage, bone, or other tissue. The scientist who named them later argued that's mostly not what happens. In 2017 he proposed renaming them "medicinal signaling cells". His argument: they act mainly by releasing signals that calm immune activity and prompt the body's own resident repair cells, rather than by becoming new tissue themselves [6].

That shift matters when you read a claim. "Regrows your cartilage" is a much bigger claim than "may change inflammatory signaling for a while", and the research supports the second far better than the first.

What the strongest studies show

Knee osteoarthritis. A 2025 Cochrane review of 25 randomized trials (1,341 people) found stem cell injections may slightly improve pain and function compared with placebo, by about 1.2 points on a 0–10 pain scale, with low-certainty evidence [7]. In the 480-person MILES trial, bone marrow, fat-derived, and cord tissue cell injections did no better than a steroid shot at one year, and no group showed a significant MRI change [8]. Full tour: Stem Cells, PRP, and Your Knees.

Low back pain from disc degeneration. In a 100-person trial, a single disc injection of donor "mesenchymal precursor cells" did better than controls on pain and disability at several time points, though disc imaging didn't change [9]. A larger follow-up trial (404 people, same company) missed its main goal, with better results only in some subgroups [10]. Both were funded by the manufacturer.

Crohn's disease fistulas: a lesson in replication. In a 212-person trial, a donor fat-derived MSC product (darvadstrocel) beat placebo for closing fistulas, 50% vs 34% [11], and Europe approved it in 2018 [15]. A second, larger trial (568 people) found almost no difference: 48.8% vs 46.3% [12]. The European approval was withdrawn in December 2024 [15]. One encouraging trial isn't the end of the story.

A rare approved use. In December 2024 the FDA approved the first MSC therapy in the U.S., Ryoncil, for children with a serious transplant complication (steroid-refractory acute graft-versus-host disease) [13]. It isn't approved for joint, back, or nerve conditions.

Nerve pain (neuropathy). See MSC Therapy for Neuropathy: What the Research Shows.

Wharton's jelly and cord tissue. See What Is Wharton's Jelly, and How Is It Different From PRP?.

Where the regulation stands (plain version)

  • One MSC product (Ryoncil) and several cord-blood stem cell products are FDA-approved, each for specific uses [2][13].

  • The FDA says regenerative medicine products have not been approved for orthopedic conditions such as osteoarthritis, back pain, or knee pain, and that these products need FDA oversight in a clinical trial before approval [2].

  • The FDA has said there are no FDA-approved exosome products [14].

If you're reading about a specific product, two useful questions are: what is its FDA status for this use, and is it being given as part of a registered clinical trial? More questions: Questions to Ask Before Stem Cell Therapy.

What's still unknown

  • Which product, dose, and number of injections (if any) helps which people.

  • Whether any benefit lasts beyond a year or two.

  • Whether lab-grown and clinic-prepared products behave the same way as the products used in published trials.

  • Long-term safety outside carefully run trials.

Research by topic

Have a question?

Email hello@vivonyx.com or ask the Vivonyx AI assistant. New to all this? Start here.

Educational content only, not medical advice. Disclaimer · How we research

References

  1. The Nobel Prize in Physiology or Medicine 1990: Joseph E. Murray and E. Donnall Thomas. NobelPrize.org. https://www.nobelprize.org/prizes/medicine/1990/summary/

  2. U.S. Food and Drug Administration. Important Patient and Consumer Information About Regenerative Medicine Therapies (June 3, 2021). https://www.fda.gov/vaccines-blood-biologics/consumers-biologics/important-patient-and-consumer-information-about-regenerative-medicine-therapies

  3. Friedenstein AJ, Chailakhjan RK, Lalykina KS. The development of fibroblast colonies in monolayer cultures of guinea-pig bone marrow and spleen cells. Cell Tissue Kinet. 1970;3(4):393-403. https://pubmed.ncbi.nlm.nih.gov/5523063/

  4. Caplan AI. Mesenchymal stem cells. J Orthop Res. 1991;9(5):641-650. https://pubmed.ncbi.nlm.nih.gov/1870029/

  5. Subramanian A, Fong CY, Biswas A, Bongso A. Comparative characterization of cells from the various compartments of the human umbilical cord shows that the Wharton's jelly compartment provides the best source of clinically utilizable mesenchymal stem cells. PLoS One. 2015;10(6):e0127992. https://pubmed.ncbi.nlm.nih.gov/26061052/

  6. Caplan AI. Mesenchymal stem cells: time to change the name! Stem Cells Transl Med. 2017;6(6):1445-1451. https://pubmed.ncbi.nlm.nih.gov/28452204/

  7. Whittle SL, Johnston RV, McDonald S, et al. Stem cell injections for osteoarthritis of the knee. Cochrane Database Syst Rev. 2025;4:CD013342. https://pubmed.ncbi.nlm.nih.gov/40169165/

  8. Mautner K, Gottschalk M, Boden SD, et al. Cell-based versus corticosteroid injections for knee pain in osteoarthritis: a randomized phase 3 trial. Nat Med. 2023;29(12):3120-3126. https://pubmed.ncbi.nlm.nih.gov/37919438/

  9. Amirdelfan K, Bae H, McJunkin T, et al. Allogeneic mesenchymal precursor cells treatment for chronic low back pain associated with degenerative disc disease: a prospective randomized, placebo-controlled 36-month study of safety and efficacy. Spine J. 2021;21(2):212-230. https://pubmed.ncbi.nlm.nih.gov/33045417/

  10. Beall DP, Bae HW, DePalma MJ, et al. Efficacy and safety of allogeneic mesenchymal precursor cells with and without hyaluronic acid for treatment of chronic low back pain: a prospective, randomized, double blind, concurrent-controlled 36-month study. Spine J. 2025;25(9):1997-2013. https://pubmed.ncbi.nlm.nih.gov/40174800/

  11. Panés J, García-Olmo D, Van Assche G, et al. Expanded allogeneic adipose-derived mesenchymal stem cells (Cx601) for complex perianal fistulas in Crohn's disease: a phase 3 randomised, double-blind controlled trial. Lancet. 2016;388(10051):1281-1290. https://pubmed.ncbi.nlm.nih.gov/27477896/

  12. Colombel JF, Garcia Olmo D, Chen ST, et al. Darvadstrocel in patients with Crohn's disease with complex perianal fistulas: the ADMIRE CD II phase 3 randomized trial. Gastroenterology. 2026;170:1562-1570. https://pubmed.ncbi.nlm.nih.gov/41790076/

  13. U.S. Food and Drug Administration. FDA Approves First Mesenchymal Stromal Cell Therapy to Treat Steroid-refractory Acute Graft-versus-host Disease (Dec 18, 2024). https://www.fda.gov/news-events/press-announcements/fda-approves-first-mesenchymal-stromal-cell-therapy-treat-steroid-refractory-acute-graft-versus-host

  14. U.S. Food and Drug Administration. Public Safety Notification on Exosome Products (Dec 6, 2019). https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/public-safety-notification-exosome-products

  15. European Medicines Agency. Alofisel (darvadstrocel): withdrawal of the marketing authorisation in the European Union (Dec 13, 2024). https://www.ema.europa.eu/en/medicines/human/EPAR/alofisel