Mesenchymal Stem Cells (MSC): The Science Behind Regenerative Therapy

What are mesenchymal stem cells?

Mesenchymal stem cells (MSCs), more formally mesenchymal stromal cells, are multipotent adult progenitor cells originally identified in bone marrow by Alexander Friedenstein in the 1970s. They are not embryonic — they exist in adult tissues throughout the body and are responsible for the routine maintenance and repair of connective tissue, bone, cartilage, tendon, and fat. They are also one of the most studied cellular populations in the history of regenerative medicine, with thousands of registered clinical trials evaluating their use in orthopedic, autoimmune, cardiovascular, and degenerative conditions.

Unlike hematopoietic stem cells (which produce blood lineages), MSCs sit in the stromal compartment of tissues and exert their effects largely by signaling, not by replacement. They are plastic-adherent in culture, can be expanded into clinically relevant numbers under controlled laboratory conditions, and can be cryopreserved for later use. This combination — accessibility, expandability, and a documented safety profile — is why they have become the most clinically translated stem cell type in the world.

Importantly, MSCs are not a single cell type with a single behavior. Cells derived from umbilical cord tissue behave differently from cells derived from bone marrow or fat. Donor age matters, passage number matters, processing matters. A clinic that talks about "stem cells" without specifying which population and from which source is glossing over the variable that most influences clinical effect — and that distinction is exactly what this page is about.

How MSCs work — signaling, not differentiation

The most common misconception about stem cell therapy is the idea that MSCs travel to damaged tissue and "become" the cells that were lost. This is mostly not what happens. The current scientific consensus, supported by more than two decades of mechanistic research, is that MSCs work primarily through paracrine signaling — they secrete factors that change the behavior of the cells already present in the tissue.

• Paracrine secretome. MSCs release a continuous mixture of growth factors (VEGF, HGF, IGF-1, TGF-β), cytokines, and chemokines that recruit local progenitor cells, dampen chronic inflammation, and stimulate angiogenesis. This "secretome" is the active pharmacology of MSC therapy and is now an area of research in its own right.
• Exosomes and extracellular vesicles. A meaningful share of the MSC paracrine effect is delivered through extracellular vesicles — small membrane-bound packages of microRNA, lipids, and proteins. Exosome-based therapeutics are an active research arm precisely because they isolate the signaling without the cells.
• Immunomodulation. MSCs interact with both arms of the immune system: they shift macrophages toward a pro-resolution M2 phenotype, suppress over-activated T cells, and induce regulatory T cells. This is the core mechanism behind their use in autoimmune and inflammatory conditions, and the reason allogeneic protocols are clinically feasible.
• Limited direct differentiation. MSCs can differentiate into bone, cartilage, and fat lineages in vitro, but the in-vivo evidence that infused MSCs engraft and become new tissue at scale is weak. Marketing language that frames therapy as "replacing damaged cells" is not consistent with the current published literature. The honest framing is signaling and immunomodulation.

The practical implication is that MSC therapy works best when the underlying tissue still has repair capacity — when there is a biology to nudge. It is most useful as a modulator of an active disease process, not as a substitute for tissue that no longer exists.

Sources we use: where the cells come from

Three sources dominate clinical practice today. Each has trade-offs in cell yield, donor age, immune profile, and processing burden. The right source for a given patient is a medical decision driven by indication, age, and the goals of the protocol.

MSC sources at a glance

Regeneris uses Wharton's jelly UC-MSCs from a COFEPRIS-registered laboratory chain for most allogeneic protocols, and autologous BM-MSC or AD-MSC when the indication and patient profile justify it. The choice is never arbitrary.

ISCT minimum criteria for MSC identification

Because "stem cell" is a loose term used by everyone from researchers to wellness marketers, the International Society for Cell & Gene Therapy (ISCT) published in 2006 a three-part minimum definition for what counts as a mesenchymal stromal cell. A reputable laboratory characterizes every batch against these criteria.

1. Plastic-adherent under standard culture conditions. MSCs must attach to tissue culture plastic when maintained in standard culture conditions. This is the operational starting point for isolation and expansion.
2. Surface marker expression. Positive for CD73, CD90, and CD105 (≥95% of the population). Negative for CD45, CD34, CD14 or CD11b, CD79α or CD19, and HLA-DR (≤2%). Verified by flow cytometry on each release lot.
3. Trilineage differentiation in vitro. Cells must be able to differentiate into osteoblasts (bone), adipocytes (fat), and chondroblasts (cartilage) under appropriate induction conditions. Documented during the laboratory's potency assays.

A clinic that cannot tell you whether its cells meet the ISCT criteria — and on what assays — is asking you to take their word. Ask for the Certificate of Analysis (CoA) for the lot that would be used in your protocol.

Conditions MSCs are being studied for

MSC therapy is investigational for most indications. The published evidence is strongest for some, emerging for others, and preliminary for many more. We list below the indication classes we routinely evaluate, with the honest caveat that mechanism is more established than efficacy in many cases.

• Knee and joint osteoarthritis. Strongest peer-reviewed evidence base. Randomized trials report meaningful symptomatic and functional improvement, often lasting 12–24 months. Frequently combined with PRP or hyaluronic acid. See our knee osteoarthritis program.
• Lumbar and cervical spine pain. Used as an adjunct to interventional pain medicine in disc-related and facet pain after conservative therapy plateaus. Indication is patient-specific and imaging-driven.
• Autoimmune conditions. Lupus, rheumatoid arthritis, Hashimoto's thyroiditis, multiple sclerosis — evaluated jointly with the patient's specialist. MSC immunomodulation rationale is mechanistically clear; clinical evidence is heterogeneous and case selection matters.
• Sports and overuse injury. Tendinopathy, partial tears, and post-surgical recovery in athletes and active adults. Often combined with PRP and structured rehabilitation.
• Long COVID and chronic post-viral inflammation. Emerging research area. Mechanism (immunomodulation, dampened chronic inflammation) maps to the proposed pathophysiology; clinical data is early.
• Hair restoration and dermatology. MSC-conditioned media and exosomes for androgenetic alopecia and skin rejuvenation — typically as adjuncts to PRP and topical therapy.

If your condition is not on this list, that does not mean MSCs are not relevant — it means we evaluate case by case and prefer to be honest about what the literature supports.

Safety profile

Across more than two decades of clinical research, MSCs have demonstrated one of the cleanest safety profiles in the cellular therapy field. Meta-analyses of allogeneic MSC trials have not identified an increased risk of tumor formation, acute infusion reactions are uncommon and typically self-limited, and rejection — the immune-mediated destruction that defines transplantation medicine — has not been a clinically significant problem for properly sourced allogeneic cells.

The reason for the low immunogenicity is biological. MSCs express low levels of HLA class I, essentially no HLA class II, and a set of immunomodulatory factors that actively dampen the recipient immune response. This is not a marketing claim; it is the consensus position across the published literature and the basis for the entire allogeneic MSC industry. The clinical consequence is that off-the-shelf Wharton's jelly UC-MSCs can be administered without HLA matching in screened patients.

That said, safety is conditional on sourcing and process. The risks that do exist — infectious disease transmission from an inadequately screened donor, bacterial contamination from a non-sterile process, batch variability from poor quality control — are entirely supply-chain risks. They are filtered out by donor screening, by laboratory accreditation, and by Certificate-of-Analysis review per lot. A regulated supply chain is what makes the safety profile of the published trials transferable to a clinical patient.

Are MSCs FDA-approved? Regulatory status in the US, Mexico & Canada

This is the question patients from the United States and Canada ask first, and it deserves a direct answer. As of this review, the U.S. Food and Drug Administration (FDA) has not approved any mesenchymal stem cell product for orthopedic, autoimmune, anti-aging, or general regenerative use. Almost all MSC therapy worldwide — including in the U.S. itself, inside registered clinical trials — is investigational. Most expanded, culture-grown MSC products are regulated by the FDA as biological drugs requiring a Biologics License Application, which is why they are not sold as routine in-office treatments in the United States (Marks & Gottlieb, New England Journal of Medicine, 2017 — "Balancing Safety and Innovation for Cell-Based Regenerative Medicine", https://www.nejm.org/doi/full/10.1056/NEJMsr1715626).

Mexico regulates these therapies under a different but real framework. The federal health authority COFEPRIS (Comisión Federal para la Protección contra Riesgos Sanitarios) oversees cellular-therapy laboratories, donor screening, and the facilities where treatment is delivered. "COFEPRIS-regulated" is not a marketing flourish — it means the laboratory chain that produces the cells and the clinic that administers them operate inside a sanitary-control system with inspections and licensing requirements (COFEPRIS, Secretaría de Salud, https://www.gob.mx/cofepris). This is the legal basis on which patients travel to Cancún for protocols that are not yet routinely available at home.

In Canada, Health Canada classifies most cell therapies as biologic drugs under the Food and Drugs Act, and — as in the U.S. — culture-expanded allogeneic MSCs are not approved for general regenerative indications outside of authorized clinical trials. The practical takeaway for international patients is that the relevant question is not "is it FDA-approved" (almost nothing in this field is, anywhere) but "is this specific clinic operating inside a real regulatory framework, with documented cell sourcing and physician oversight?" We unpack that comparison in our Mexico-vs-USA guide and our how-to-choose-a-clinic checklist.

Why benefits can outlast the cells: the engraftment paradox

One of the most counter-intuitive findings in the MSC literature is that the great majority of infused cells do not survive long-term in the recipient. After intravenous delivery, most MSCs are trapped in the lungs within hours and are cleared by the recipient's own immune system over the following days to weeks; durable engraftment into target tissue is rare and is not the main driver of clinical effect (Eggenhofer E, et al., "Mesenchymal stem cells are short-lived and do not migrate beyond the lungs after intravenous infusion", Frontiers in Immunology, 2014, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4068291/).

So why would any benefit persist for months when the cells themselves are gone in weeks? The current explanation is that MSCs act less like a tissue graft and more like a short-lived biological signal. While present, they reprogram the local immune environment — shifting macrophages toward a pro-resolution state, calming over-active T cells, and releasing pro-repair growth factors and exosomes. That reset of the inflammatory milieu can persist after the cells are cleared, because the change is to the patient's own tissue and immune cells, not to a population of foreign cells that must survive indefinitely. Andrew Caplan, who named the field, has argued the cells are better understood as "medicinal signaling cells" precisely for this reason (Caplan AI, "Mesenchymal Stem Cells: Time to Change the Name!", Stem Cells Translational Medicine, 2017, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5442724/).

This mechanism also explains why exosome-based and cell-free approaches are an active research arm — they aim to deliver the signal without the cells — and why protocols are often structured as a course with periodic boosters rather than a single permanent "fix." It is the honest framing of what the therapy does: it nudges a biological process, and the durability of that nudge varies by indication and by patient.

What the clinical evidence actually shows

"There is evidence" and "it is proven to work" are not the same statement, and an honest page has to keep them apart. Below is a sober read of the two indication classes with the strongest peer-reviewed data. The pattern across them is consistent: randomized trials show statistically significant symptomatic and functional improvement that is durable for many patients, while still being classed as investigational, with effect sizes and durability that vary from one person to the next.

• Knee osteoarthritis — the strongest evidence base. Knee OA is where MSC therapy has been studied most rigorously. In a randomized controlled trial comparing allogeneic bone-marrow MSCs against hyaluronic acid, the cell-treated group showed significant improvement in pain and function over one year, alongside a measurable decrease in poor-cartilage areas on quantitative T2 MRI mapping (Vega A, et al., Transplantation, 2015, https://doi.org/10.1097/TP.0000000000000678). A separate proof-of-concept trial reported reduced cartilage-defect size and hyaline-like cartilage on arthroscopy in the higher-dose group, with no treatment-related adverse events (Jo CH, et al., Stem Cells, 2014, https://doi.org/10.1002/stem.1634). Longer-term follow-up of a multicenter randomized trial found the functional benefit persisted out to roughly 12 months and beyond in treated patients (Lamo-Espinosa JM, et al., Journal of Translational Medicine, 2018, https://doi.org/10.1186/s12967-018-1591-7). The realistic framing patients should hold onto: meaningful, statistically significant improvement in symptoms and function — frequently in the range of one to two years of benefit — not a guaranteed outcome and not cartilage "regrown to new." We cover the joint program in detail on our knee treatment page.
• Systemic lupus & lupus nephritis — promising, heterogeneous. For autoimmune disease the evidence is genuinely promising but more heterogeneous than the knee data. Multicenter work on umbilical-cord MSC transplantation in active and refractory systemic lupus erythematosus reported clinical improvement in disease-activity scores in a meaningful share of otherwise treatment-resistant patients (Wang D, et al., Arthritis Research & Therapy, 2014, https://doi.org/10.1186/ar4520), and a randomized, double-blind, placebo-controlled trial specifically in lupus nephritis has been published — the most rigorous study design in this indication (Deng D, et al., Annals of the Rheumatic Diseases, 2017, https://doi.org/10.1136/annrheumdis-2017-211073). The honest caveat is that results have not been uniform across all lupus trials, case selection clearly matters, and MSC therapy here is evaluated jointly with the patient's treating rheumatologist rather than as a replacement for standard immunosuppression.

Two principles follow from the literature as a whole. First, the mechanism (immunomodulation and paracrine signaling) is more firmly established than the efficacy for any single condition — which is exactly why these protocols remain investigational. Second, no responsible clinic can quote you a personal "success rate": published trial averages describe populations, not individuals, and your realistic expectation can only be set after a physician reviews your diagnosis, imaging, and history.

Why passage number matters (and what "low passage" means)

When a clinic says it uses "low-passage" cells, that phrase has real biological content and is worth understanding. "Passage" counts how many times a cell population has been detached and re-plated as it is expanded in the laboratory. Each passage is another round of division — and MSCs do not divide indefinitely without changing. The landmark analysis here showed that replicative senescence in MSC cultures is a continuous, organized process that begins from the very first passages onward, with progressive shifts in morphology, surface-marker expression, gene-expression and microRNA profiles, and differentiation potential (Wagner W, et al., "Replicative Senescence of Mesenchymal Stem Cells: A Continuous and Organized Process", PLOS ONE, 2008, https://doi.org/10.1371/journal.pone.0002213).

The practical consequence is that cells expanded too far drift away from the very definition that makes them MSCs. The ISCT minimum criteria — the CD73/CD90/CD105-positive, CD45/CD34/HLA-DR-negative surface profile and trilineage differentiation discussed above — are precisely the properties that erode with excessive passaging (Dominici M, et al., Cytotherapy, 2006, https://doi.org/10.1080/14653240600855905). This is why serious laboratories define and record a release window of early passages and keep clinically administered cells within it, rather than maximizing yield by culturing cells as long as possible.

For a patient, this turns into one concrete, answerable question: at what passage are the cells I would receive, and does the Certificate of Analysis confirm they still meet the ISCT marker and viability thresholds at that passage? A clinic that tracks passage number and can show you the CoA is operating the way the science says it should. We put this and other verifiable questions into our how-to-choose-a-clinic checklist.

Quality control at Regeneris

Every batch of cells used at Regeneris goes through a documented release process before it is approved for clinical use. We treat this paperwork as part of the protocol, not as a back-office detail.

• Flow cytometry characterization. ISCT-aligned panel — CD73+, CD90+, CD105+ (positive markers ≥95%) and CD45−, CD34−, CD14−, CD19−, HLA-DR− (negative markers ≤2%). Run on every release lot.
• Viability assay. Trypan blue or 7-AAD viability assessment. Lots are released only if viability meets the laboratory's pre-set threshold for the cell type and passage in question.
• Sterility and endotoxin testing. USP <71> or equivalent sterility test plus limulus amebocyte lysate (LAL) endotoxin assay. No lot is released with a positive sterility result or an endotoxin value above the pharmacopeial limit.
• Mycoplasma screening. PCR-based mycoplasma testing on the master and working cell banks, in line with regulatory expectations for cellular therapeutics.
• Identity and passage tracking. Each lot is traceable to the donor and the passage number. Cells used clinically are kept at low passage to preserve potency.
• Certificate of Analysis (CoA) per dose. Every dose administered is accompanied by a Certificate of Analysis summarizing the above. Patients can request a copy for their records.

Frequently asked questions

Mesenchymal stem cell therapy is investigational for many indications. Evidence varies by condition. Individual results vary, and individualized medical evaluation is required before any protocol is recommended. This page is for educational purposes and does not constitute medical advice.