Five potency classes, four cell origins, and one distinction that decides almost everything: which of these is approved medicine, and which is not.
Two Classification Systems
By potency — how much a cell can become
⚠️ *This is a hierarchy of biological capability, not of clinical usefulness — and definitely not of evidence. A more potent cell is not a better treatment. The most clinically established therapy in this whole field uses multipotent* cells (HSCs); the most potent classes remain largely experimental.
By origin — where a cell comes from
Embryonic stem cells (ESCs). Derived from the blastocyst [5]. Pluripotent. ⚠️ Teratoma risk if not fully differentiated before transplantation — a real, class-specific hazard. Ethically contested. Research and early trials only.
Adult (tissue-resident) stem cells. Multipotent, present from birth onward, maintaining the tissues where they reside. This class contains both the best-established stem cell therapy in medicine and the one sold commercially — and they are not the same cells.
Induced pluripotent stem cells (iPSCs). Adult cells reprogrammed to pluripotency using defined factors [11]— the discovery for which Yamanaka shared the Nobel Prize. ⚠️ Carries the same teratoma risk as ESCs, and the field's own assessment of clinical translation remains one of promise alongside substantial challenges [3]. Largely preclinical; a small number of early trials.
Perinatal stem cells. From umbilical cord tissue (Wharton's jelly), cord blood and placenta. Cord tissue MSCs have a well-characterised literature [12].
The Two Cell Types That Matter Clinically — And Why They Are Not Comparable
Both are multipotent. Both are adult stem cells. Their evidence bases are separated by roughly fifty years, and this is the most important thing on this page.
Haematopoietic stem cells (HSCs) — approved standard of care
HSCs give rise to every blood and immune cell type. Transplantation dates to the first intravenous bone-marrow infusions in patients receiving radiation and chemotherapy [6]and is now routine curative-intent therapy for leukaemias, lymphomas and marrow failure [10]. Sources: bone marrow, mobilised peripheral blood, cord blood. Ex-vivo expansion is an active area of development [16].
This is real, approved, reimbursed medicine with decades of controlled data.
Mesenchymal stromal cells (MSCs) — investigational
Also called: mesenchymal stromal cells — the designation used by the International Society for Cellular Therapy [8]— and medicinal signalling cells, the term proposed by Arnold Caplan, who coined "mesenchymal stem cell" and has since argued the name misleads [7].
⚠️ The naming dispute is worth understanding rather than glossing. "Stem cell" implies replacement of damaged tissue; the evidence points to signalling. Both alternative names come from the field's own authorities.
Found in: bone marrow, adipose tissue, umbilical cord tissue (Wharton's jelly), cord blood, dental pulp, synovial fluid. Their accessibility, expandability and low immunogenicity are the practical reasons they dominate clinical investigation among adult cell types [2]— ⚠️ reasons of convenience and tractability, which are not the same as evidence of superior effect.
ISCT minimal identifying criteria [8]:
- Plastic adherence in culture
- Surface markers CD105+, CD73+, CD90+; negative for CD45, CD34, CD14, CD19, HLA-DR
- *Tri-lineage differentiation in vitro: bone, cartilage and fat — three lineages*
⚠️ Only those three. Myogenic differentiation is sometimes listed as a fourth; it is not part of the ISCT criteria and should not be presented as an established MSC capability.
⚠️ And these are laboratory identity criteria, not a description of what happens after injection. MSCs are also immune evasive rather than immune privileged [4]— a distinction that matters for repeat allogeneic dosing.
One MSC product has full regulatory approval anywhere in the world, for graft-versus-host disease. Everything else described on this page is investigational.
Comparison
⚠️ The regulatory row is the one that should drive a decision, and it is the row most often left out of comparisons like this.
⚠️ Two risks are frequently confused, in both directions. Teratoma formation is a pluripotent-cell risk and is not an MSC risk. Tumour promotion — the possibility that MSCs could support the growth of a tumour already present — is a separate, open question that applies to MSCs and not to teratoma-forming cells. Neither should be borrowed to describe the other.
A note on NK and NKT cells. These appear in some comparisons of "stem cell types." They are not stem cells — they are mature immune cells, and adoptive NK cell therapy is a distinct field with its own evidence base in oncology [18]. They are excluded here because a classification that includes non-members is not a classification.
What Each Type Is Actually Used For
Blood cancers and marrow failure — HSCs
Reconstitution of the entire blood and immune system after high-dose chemotherapy or radiation [10][16]. Approved, established, curative in many cases.
Musculoskeletal conditions — MSCs
The best-studied MSC indication. A comprehensive appraisal of 15 randomised controlled trials and 11 non-randomised trials in knee osteoarthritis found [13]:
- Function improved in 12 of 15 RCTs versus baseline and 11 of 15 versus control
- Cartilage protection or repair in 18 of 21 clinical studies
- ⚠️ "The relatively small sample size of 610 patients limited the drawing of definitive conclusions" — the authors' own words
Which source? The only head-to-head comparison is a network meta-analysis of 15 studies and 585 patients [22]:
"MSCs transplantation effectively treats KOA patients, with autologous BM-MSC potentially offering more excellent benefits."
⚠️ Both halves matter. The therapy works; and the source that performed best was autologous bone marrow, not umbilical cord.
Respiratory conditions — MSCs
Systematic review and meta-analysis of stem-cell-based regenerative therapy in COPD [14]. ⚠️ Much of the supporting evidence in this area remains experimental.
Neurological conditions — mostly preclinical
Regenerative stem cell approaches to neurodegenerative disease are an active research area [15]. ⚠️ Overwhelmingly preclinical or early-phase. No stem cell therapy is approved for Parkinson's disease, stroke or spinal cord injury.
Aging and frailty — MSCs, in patients with frailty
Randomised placebo-controlled trials exist [19][20]. ⚠️ Every participant in these trials had diagnosed frailty. They are trials of a treatment for a condition, not evidence about well people.
Cell Source: What Is Established and What Is Not
What is true about donor age: the number and functional characteristics of MSCs do decline with donor age, and neonatal tissue does not carry that decline. Neonatal cord tissue is also a source of extracellular vesicles carrying anti-aging signals, which rejuvenate senescing adult bone-marrow MSCs [21]. ⚠️ That work concerns extracellular vesicles rather than cells, and its in-vivo experiments were conducted in aged mice.
⚠️ What is not established: "potency." Potency in cell therapy is a defined regulatory term requiring a validated assay tied to mechanism of action. No such assay is cited for any product described here, and the word should not be used as though one existed. Faster proliferation in culture is a laboratory attribute, not a demonstrated clinical advantage — and the only head-to-head comparison points toward bone marrow [22].
What Predicts Response
The parameters identified as shaping MSC effectiveness are cell dose, tissue of origin, autologous versus allogeneic source, and patient clinical phenotype, endotype, age, sex and level of disease severity [13].
⚠️ Disease severity predicts response — less advanced structural disease tends to respond better than end-stage. Everyone in that evidence has the disease. It is not a finding that healthy people respond better than unwell people; that comparison has never been made, because no trial has enrolled healthy people.
Evaluating a Provider
Questions worth asking:
- What cell type is being used — and is it a stem cell at all?
- What is the source (bone marrow, adipose, umbilical cord)?
- Autologous or allogeneic?
- What is the regulatory status of this product, in this country, for this indication?
- What evidence exists for this cell type in my condition — and in patients like me?
- What are the risks, and how are adverse events recorded and reported?
Red flags:
- A clinic that cannot tell you the cell type and source precisely
- "Stem cells" used as a single undifferentiated category, as though type did not matter
- Claims of benefit across a long list of unrelated conditions
- Any suggestion that availability equals approval
- Pressure to decide quickly, or pricing that changes on the call
The ISSCR guidelines set out what legitimate clinical translation looks like and are worth reading before committing to anything [17].
Frequently Asked Questions
Which type is "best"?
There is no best type — the question is which type has evidence for your condition. HSCs for blood cancers are approved and curative. MSCs for knee osteoarthritis have multiple RCTs and a small total evidence base. iPSCs for anything are largely preclinical. A more potent cell is not a better treatment.
Are embryonic stem cells used in treatments I might receive?
No. ESC-based therapies are confined to research and early-phase trials.
Do stem cell treatments use fetal tissue?
No. Umbilical cord tissue is collected after a normal birth, with consent, from tissue that is otherwise discarded. It is perinatal, not fetal.
Autologous or allogeneic?
Autologous means your own cells — no rejection risk, but a harvest procedure and cells that carry your age. Allogeneic means donor cells — no harvest, immediate availability, and consistent starting material. ⚠️ MSCs are immune evasive rather than immune privileged [4], so allogeneic does not mean immunologically invisible. The one head-to-head comparison favoured autologous bone marrow [22].
Are iPSCs available for treatment now?
Not outside clinical trials. The field's own assessment describes real promise alongside substantial unresolved challenges, including teratoma risk [3].
I'm healthy — should I consider this?
No trial has studied stem cell therapy in healthy people, for prevention, optimisation or longevity. The frailty trials [19][20]enrolled patients with diagnosed frailty. Anything offered to a well person on this basis is an extrapolation, and should be described as one.
The Bottom Line
The classification matters because the differences are real. Pluripotent cells can become anything and carry teratoma risk. Multipotent cells cannot and do not. HSC transplantation is approved medicine with decades of data. MSC therapy is investigational, promising in knee osteoarthritis, and unstudied in healthy people.
Anyone who talks about "stem cells" as a single thing is either simplifying or selling.