Stem cell research studies cells that can renew themselves and give rise to specialized cells (in the adult body, stem cells keep this ability throughout life[1]), with two aims: to understand how tissues develop, renew and fail, and to turn that knowledge into treatments. This overview covers the main cell types under study, how a cell therapy moves from the laboratory to approval, which products regulators have approved, what the largest trials have shown, how the research is governed, and how to judge a trial or clinic claim. Current studies, selected from trial registries, are listed on our page of stem cell clinical trials.
Types of Stem Cells
Stem cells are grouped by how many cell types they can make. A totipotent cell, such as the fertilized egg, can form an entire organism, including the placenta and membranes;[2] a pluripotent cell can give rise to cells of all three germ layers, and so to every cell type of the body;[3] a multipotent cell is committed to a particular family of cells.[4] Definitions of these and related terms are on our pages on multipotent stem cells, progenitor cells and differentiation.
| Cell type | Where it comes from | Range of cell types | Main uses today |
|---|---|---|---|
| Embryonic stem cells | The inner cells of an early embryo (blastocyst); first human lines reported in 1998[5] | Pluripotent[5] | Research; early-phase trials of cells made from them[6] |
| Induced pluripotent stem cells (iPSCs) | Adult cells reprogrammed in the laboratory; mouse in 2006, human in 2007[7][8] | Pluripotent[9] | Disease models; early trials; two conditional approvals in Japan[10] |
| Somatic (adult) stem cells, such as blood-forming stem cells | Tissues after birth, including bone marrow, blood and skin[11] | They maintain and repair their own tissue and, without laboratory manipulation, make only that tissue’s cell types[11][12] | Blood stem cell transplantation, the best-established stem cell treatment[12] |
| Mesenchymal stromal cells (MSCs) | Bone marrow, fat, umbilical cord tissue and other tissues[13] | Bone, cartilage and fat cells in the laboratory[14] | A few narrowly approved products; most uses investigational[15][10] |
Embryonic stem cells. The first human embryonic stem cell lines, derived from blastocysts in 1998, kept their normal chromosomes after months of growth in the laboratory and could still form tissues of all three germ layers, including gut lining, cartilage, bone, muscle and nerve tissue.[5] Trials transplant specialised cells made from them, such as nerve-cell precursors, rather than the stem cells themselves.[6] More is on our page on embryonic stem cells.
Induced pluripotent stem cells. In 2006, Takahashi and Yamanaka turned mouse fibroblasts, a common connective tissue cell, into pluripotent cells by adding four genes, Oct3/4, Sox2, c-Myc and Klf4;[7] in 2007 the same four factors reprogrammed adult human skin cells into cells that resembled embryonic stem cells and could form cells of all three germ layers.[8] Because iPSCs can be made from any person, they allow disease-specific cell lines to be grown for study.[8] Our page on induced pluripotent stem cells describes how they are made and their risks.
Somatic stem cells. Also called adult or tissue-specific stem cells, they appear during fetal development, stay in the body for life and maintain and repair the tissue in which they live, such as skin or blood.[11] Without manipulation in the laboratory, they make only the cell types of their own tissue: blood-forming stem cells make blood cells, not brain cells.[12] Examples are covered on our pages on somatic stem cells, neural stem cells and the stem cell niche that controls them, and the two main groups are compared on our page on somatic and embryonic stem cells.
From Laboratory to Approved Treatment
A cell product is first tested in the laboratory and in animals, then in clinical trials in people. The US Food and Drug Administration (FDA) describes the usual sequence for a new medicine: phase 1 studies in 20 to 100 people over several months, mainly for safety and dose; phase 2 studies in up to several hundred people with the condition, for effectiveness and side effects; and phase 3 studies, sometimes called pivotal studies, in 300 to 3,000 people over 1 to 4 years, to show whether the product benefits a specific population and to collect most of the safety data. In the FDA’s figures, about 70% of drugs move on from phase 1, about 33% from phase 2 and 25 to 30% from phase 3.[16]
Trials are registered in public databases such as ClinicalTrials.gov, but registration is not approval: the FDA warns that a product’s inclusion in ClinicalTrials.gov does not mean it is legally marketed.[17] Some US businesses selling stem cell interventions without FDA approval have listed “pay-to-participate” studies on ClinicalTrials.gov, in which participants are charged for the treatment, and used the listing to recruit clients.[18] Japan also grants conditional, time-limited approvals of regenerative medical products, as for several products on its list.[10]
What Regulators Have Approved
As of November 2026, the FDA list of approved cellular and gene therapy products (updated 30 October 2026) includes nine cord blood products of blood-forming stem cells (listed as HPC, Cord Blood), omidubicel (OMISIRGE), one mesenchymal stromal cell product (remestemcel-L, RYONCIL) and no product made from embryonic or induced pluripotent stem cells; most of its other entries are gene therapies and genetically modified cell products.[15] Blood-forming stem cell transplantation for certain blood and immune disorders, and to rebuild the blood system after some cancer treatments, is the best-established stem cell treatment; tissue grafts for some bone, skin and corneal injuries are also accepted, and the International Society for Stem Cell Research (ISSCR) advises that all other uses be considered highly experimental.[12]
In the European Union, Holoclar, made from a patient’s own corneal cells containing limbal stem cells, is authorised for adults with moderate to severe limbal stem cell deficiency after eye burns; it received conditional authorisation on 17 February 2015, switched to standard authorisation on 22 February 2024.[19] The EU authorisation of darvadstrocel (Alofisel), donor fat-derived MSCs for perianal fistulas in Crohn’s disease, issued on 23 March 2018, was withdrawn on 13 December 2024.[20]
Japan’s list of approved regenerative medical products (April 2015 to July 2026) contains the first approvals of products made from induced pluripotent stem cells. On 6 March 2026, two received conditional, time-limited approval: AMCHEPRY (raguneprocel), dopamine-producing nerve precursor cells made from donor iPSCs and transplanted into the brain for Parkinson’s disease that responds inadequately to medicines including levodopa, and RiHEART, sheets of heart muscle cells made from donor iPSCs and placed on the heart for severe heart failure from ischemic cardiomyopathy that responds inadequately to standard care.[10] The MSC products on the same list are described in the next section. A wider table of approved regenerative products is on our page on regenerative medicine.
Mesenchymal Stem Cell Therapies
Mesenchymal stromal cells, also called mesenchymal stem cells, are multipotent cells that do not make blood and are found in bone marrow, fat, umbilical cord tissue (Wharton’s jelly) and other tissues.[13] Because laboratories prepared and described them in different ways, the International Society for Cellular Therapy set minimum criteria in 2006: the cells must stick to plastic in culture, carry the surface markers CD105, CD73 and CD90 while lacking blood-cell markers such as CD45 and CD34, and form bone, fat and cartilage cells in the laboratory.[14] How bone marrow is collected from the pelvis is described on our page on the iliac crest.
Approvals of MSC products are few and each covers one narrow use. The only MSC product on the FDA list is remestemcel-L.[15] Japan’s list includes donor bone marrow MSCs given by infusion for acute graft-versus-host disease after a blood stem cell transplant (TEMCELL HS, approved 18 September 2015); donor fat MSCs for complex perianal fistulas in Crohn’s disease (Alofisel, 27 September 2021); the patient’s own bone marrow MSCs given by infusion for traumatic spinal cord injury (STEMIRAC, conditional, time-limited approval 28 December 2018); modified donor bone marrow MSCs implanted in the brain for chronic weakness after traumatic brain injury (Akuugo, conditional approval 31 July 2024); donor fat MSC sheets for skin erosions in epidermolysis bullosa (Allostem Sheet, 3 April 2026); and a patient’s own knee synovium MSCs for a meniscal tear repaired by suturing (Savyscus, 8 May 2026).[10] The list records approvals, not later withdrawals: after the EU withdrawal, the company said it was engaging health authorities in the other countries where Alofisel was approved.[21] Outside approved products and their stated uses, MSC treatment is investigational.
Large trials have produced both positive and negative results, and a positive first trial does not always hold up:
| Condition and product | Trial | Result |
|---|---|---|
| Crohn’s perianal fistulas: darvadstrocel, donor fat MSCs | Phase 3, randomized, placebo-controlled; 568 patients[22] | No benefit: remission at 24 weeks in 48.8% with cells and 46.3% with placebo |
| Knee osteoarthritis: bone marrow concentrate, fat stromal vascular fraction or donor umbilical cord MSCs | Phase 2/3, randomized against a steroid injection; 480 patients[23] | No cell injection better than the steroid for pain at 12 months; no change in MRI scores |
| Crohn’s perianal fistulas: darvadstrocel | Phase 3, randomized, placebo-controlled; 212 patients[24] | Combined remission at 24 weeks in 50% with cells and 34% with placebo; not confirmed by the larger trial above |
| Amyotrophic lateral sclerosis: the patient’s own bone marrow MSCs grown to release nerve growth factors, injected into the spinal fluid | Phase 3, randomized, placebo-controlled; 196 patients[25] | No benefit on the main outcome: 33% responders with cells and 28% with placebo |
How MSCs act in the body is still being studied; the signals cells release and their effects on the immune system are covered on our pages on paracrine signaling and immunomodulation.
Pluripotent Stem Cells in the Clinic
Parkinson’s disease, caused by the loss of dopamine-producing neurons, is where cells made from pluripotent stem cells have gone furthest. In a phase 1/2 trial at Kyoto University Hospital, seven people aged 50 to 69 received dopamine-cell progenitors made from donor iPSCs. There were no serious adverse events and no graft overgrowth on MRI, although dyskinesia (involuntary movements) increased because medication doses were mostly kept unchanged; of six patients assessed for effect, four improved on the motor score measured off medication, and dopamine production in the treated area rose by 44.7% on PET scans.[26] In an open-label phase 1 trial of bemdaneprocel, dopamine-neuron progenitors made from embryonic stem cells, 12 patients had no adverse events related to the cells at one year, and PET scans at 18 months suggested that the grafts survived.[6] Neither trial had a control group, and the approval of AMCHEPRY in Japan is conditional and time-limited.[10]
Ethics and Oversight
The debate about the moral status of the embryo still shapes embryonic stem cell research, but other questions apply to all stem cell work: the safety of iPSC-derived products in early trials, consent, control and justice when cells from sources such as umbilical cord blood, fat or amniotic fluid are banked, and the risk of the “therapeutic misconception” among trial participants.[27]
The ISSCR guidelines, last fully revised in 2021, sort research into categories of review. Deriving cell lines from human embryos and culturing embryos for research belong to a category that needs specialised scientific and ethics review, while heritable genome editing for reproduction is not allowed. The 2021 revision also removed the fixed ban on culturing human embryos beyond 14 days, recommending instead that any proposal to go further wait for public discussion led by national academies, funders and regulators, and it cautions forcefully against the premature commercialisation of unproven stem cell interventions.[28] A targeted update in August 2025 revised only the section on stem cell-based embryo models; all other sections remain as published in 2021.[29] National laws differ, and our page on embryonic stem cells gives examples.
How to Judge a Trial or Clinic Claim
Stem cell interventions without regulatory approval are marketed directly to patients, not only in countries with weak regulation; an analysis of internet marketing found widespread promotion by businesses based in the United States.[30] The FDA states that regenerative medicine products require its approval before they are marketed and its oversight in a clinical trial before approval, and it has received reports of blindness, tumour formation and infections after products used without approval.[17] The ISSCR advises patients to be wary of treatments offered without regulatory approval or outside a legitimate, registered clinical trial, and of any clinic offering one cell type for many unrelated diseases.[12] Useful questions are:
- Is the product approved for this condition by a named regulator, and when? The regulator’s own list answers this.[15][10]
- Is the study registered, has a regulator permitted it, and are participants charged to take part?[18]
- What phase is it, how many people took part, and was there a control group? Phase 1 studies test mainly safety and dose.[16]
- Have the results been published, including negative ones, and has a larger trial confirmed a positive first result?[22][24]
Published Clinical Citations
[1] ^ National Library of Medicine. Stem Cells (MeSH descriptor D013234). Medical Subject Headings. https://meshb.nlm.nih.gov/record/ui?ui=D013234
[2] ^ National Library of Medicine. Totipotent Stem Cells (MeSH descriptor D039901). Medical Subject Headings. https://meshb.nlm.nih.gov/record/ui?ui=D039901
[3] ^ National Library of Medicine. Pluripotent Stem Cells (MeSH descriptor D039904). Medical Subject Headings. https://meshb.nlm.nih.gov/record/ui?ui=D039904
[4] ^ National Library of Medicine. Multipotent Stem Cells (MeSH descriptor D039902). Medical Subject Headings. https://meshb.nlm.nih.gov/record/ui?ui=D039902
[5] ^ Thomson JA, Itskovitz-Eldor J, Shapiro SS, et al. Embryonic stem cell lines derived from human blastocysts. Science. 1998;282(5391):1145-1147. https://doi.org/10.1126/science.282.5391.1145
[6] ^ Tabar V, Sarva H, Lozano AM, et al. Phase I trial of hES cell-derived dopaminergic neurons for Parkinson’s disease. Nature. 2025;641(8064):978-983. https://doi.org/10.1038/s41586-025-08845-y
[7] ^ Takahashi K, Yamanaka S. Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell. 2006;126(4):663-676. https://doi.org/10.1016/j.cell.2006.07.024
[8] ^ Takahashi K, Tanabe K, Ohnuki M, et al. Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell. 2007;131(5):861-872. https://doi.org/10.1016/j.cell.2007.11.019
[9] ^ National Library of Medicine. Induced Pluripotent Stem Cells (MeSH descriptor D057026). Medical Subject Headings. https://meshb.nlm.nih.gov/record/ui?ui=D057026
[10] ^ Pharmaceuticals and Medical Devices Agency (Japan). List of Approved Regenerative Medical Products, April 2015 to July 2026. https://www.pmda.go.jp/files/000283257.pdf
[11] ^ National Library of Medicine. Adult Stem Cells (MeSH descriptor D053687). Medical Subject Headings. https://meshb.nlm.nih.gov/record/ui?ui=D053687
[12] ^ International Society for Stem Cell Research. Nine Things to Know About Stem Cell Treatments. A Closer Look at Stem Cells. https://www.closerlookatstemcells.org/stem-cells-medicine/nine-things-to-know-about-stem-cell-treatments/
[13] ^ National Library of Medicine. Mesenchymal Stem Cells (MeSH descriptor D059630). Medical Subject Headings. https://meshb.nlm.nih.gov/record/ui?ui=D059630
[14] ^ Dominici M, Le Blanc K, Mueller I, et al. Minimal criteria for defining multipotent mesenchymal stromal cells. The International Society for Cellular Therapy position statement. Cytotherapy. 2006;8(4):315-317. https://doi.org/10.1080/14653240600855905
[15] ^ US Food and Drug Administration. Approved Cellular and Gene Therapy Products. Content current as of 30 October 2026. https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/approved-cellular-and-gene-therapy-products
[16] ^ US Food and Drug Administration. The Drug Development Process. Step 3: Clinical Research. Content current as of 4 January 2018. https://www.fda.gov/patients/drug-development-process/step-3-clinical-research
[17] ^ US Food and Drug Administration. Important Patient and Consumer Information About Regenerative Medicine Therapies. 3 June 2021; content current as of 8 April 2024. https://www.fda.gov/vaccines-blood-biologics/consumers-biologics/important-patient-and-consumer-information-about-regenerative-medicine-therapies
[18] ^ Turner L. ClinicalTrials.gov, stem cells and ‘pay-to-participate’ clinical studies. Regenerative Medicine. 2017;12(6):705-719. https://doi.org/10.2217/rme-2017-0015
[19] ^ European Medicines Agency. Holoclar: EPAR (ex vivo expanded autologous human corneal epithelial cells containing stem cells). https://www.ema.europa.eu/en/medicines/human/EPAR/holoclar
[20] ^ European Medicines Agency. Alofisel (darvadstrocel): EPAR, medicine withdrawn. https://www.ema.europa.eu/en/medicines/human/EPAR/alofisel
[21] ^ Takeda Pharmaceutical Company. Takeda provides an update on Alofisel (darvadstrocel). Statement, 13 December 2024. https://www.takeda.com/newsroom/statements/2024/takeda-alofisel-update-2024/
[22] ^ 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(7):1562-1570. https://doi.org/10.1053/j.gastro.2025.12.033
[23] ^ Mautner K, Gottschalk M, Boden SD, et al. Cell-based versus corticosteroid injections for knee pain in osteoarthritis: a randomized phase 3 trial. Nature Medicine. 2023;29(12):3120-3126. https://doi.org/10.1038/s41591-023-02632-w
[24] ^ 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://doi.org/10.1016/S0140-6736(16)31203-X
[25] ^ Cudkowicz ME, Lindborg SR, Goyal NA, et al. A randomized placebo-controlled phase 3 study of mesenchymal stem cells induced to secrete high levels of neurotrophic factors in amyotrophic lateral sclerosis. Muscle & Nerve. 2022;65(3):291-302. https://doi.org/10.1002/mus.27472
[26] ^ Sawamoto N, Doi D, Nakanishi E, et al. Phase I/II trial of iPS-cell-derived dopaminergic cells for Parkinson’s disease. Nature. 2025;641(8064):971-977. https://doi.org/10.1038/s41586-025-08700-0
[27] ^ King NM, Perrin J. Ethical issues in stem cell research and therapy. Stem Cell Research & Therapy. 2014;5(4):85. https://doi.org/10.1186/scrt474
[28] ^ Lovell-Badge R, Anthony E, Barker RA, et al. ISSCR Guidelines for Stem Cell Research and Clinical Translation: the 2021 update. Stem Cell Reports. 2021;16(6):1398-1408. https://doi.org/10.1016/j.stemcr.2021.05.012
[29] ^ International Society for Stem Cell Research. ISSCR Guidelines for Stem Cell Research and Clinical Translation, version 1.2 (August 2025 update). https://www.isscr.org/guidelines
[30] ^ Turner L, Knoepfler P. Selling stem cells in the USA: assessing the direct-to-consumer industry. Cell Stem Cell. 2016;19(2):154-157. https://doi.org/10.1016/j.stem.2016.06.007