Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis, peripheral blood cytopenias, and a variable risk of transformation to acute myeloid leukemia. MDS affects approximately 4–5 per 100,000 individuals annually, rising to 30–50 per 100,000 in those over 70 years of age [1].

Where conventional treatments fall short. The only curative therapy for MDS is allogeneic hematopoietic stem cell transplantation, which is limited to younger, fit patients with suitable donors and carries a 15–30% transplant-related mortality risk. For the majority of patients, treatment focuses on disease modification with hypomethylating agents (azacitidine, decitabine), lenalidomide for del(5q) MDS, and supportive care with transfusions and growth factors. Hypomethylating agents achieve hematologic improvement in only 40–50% of patients, with a median response duration of 12–18 months. When these agents fail, therapeutic options narrow dramatically [2].

The deeper problem is niche-level pathology. MDS is not simply a hematopoietic stem cell disease — it is a disease of the bone marrow microenvironment. The MDS clone remodels its surrounding niche through secretion of inflammatory cytokines including TNF-α, IL-6, and TGF-β, which suppress normal hematopoietic stem cells while promoting clonal expansion. The stromal compartment becomes fibrotic and pro-inflammatory, losing its capacity to support effective multilineage hematopoiesis. Concurrently, the immune microenvironment shifts toward myeloid-derived suppressor cell expansion and CD8+ T-cell exhaustion, creating an immunological milieu that tolerates the malignant clone while failing to eliminate it. This niche-level dysfunction explains why therapies targeting only the malignant clone — without repairing the microenvironment — produce incomplete and transient responses [3].

MSC therapy targets both the clone and the niche. Mesenchymal stem cells are the native stromal cells of the bone marrow niche — the very cells that support normal hematopoiesis and maintain microenvironmental homeostasis. In MDS, the endogenous MSC population is functionally impaired by the malignant clone. Therapeutic infusion of healthy allogeneic MSCs delivers a coordinated program of niche restoration, inflammatory cytokine modulation, and hematopoietic support that addresses the disease at the stromal level where conventional pharmacotherapy cannot reach. Unlike hypomethylating agents, which directly target clonal cells but leave the niche damaged, MSC therapy aims to re-establish a functional bone marrow environment capable of supporting effective, multilineage hematopoiesis [4].

How MSCs Target MDS Pathophysiology

MSCs address myelodysplastic syndromes through four interconnected mechanisms, each mapped to a specific node in the disease cascade [5].

Inflammatory cytokine modulation and niche repair. The MDS bone marrow niche is characterized by elevated concentrations of TNF-α, IL-6, IL-8, and TGF-β — a pro-inflammatory milieu that suppresses normal hematopoietic stem cells, promotes clonal dominance, and drives stromal fibrosis. MSCs secrete a broad panel of anti-inflammatory mediators including prostaglandin E2, TSG-6, and IL-1 receptor antagonist that directly neutralize this inflammatory cascade. In co-culture models, bone marrow-derived MSCs reduced TNF-α and IL-6 secretion by MDS stromal cells by 55–70% and restored the capacity of the niche to support normal CD34+ hematopoietic stem and progenitor cell expansion [6].

Re-establishment of effective hematopoiesis. In MDS, the bone marrow is paradoxically hypercellular yet ineffective — hematopoietic precursors proliferate but undergo intramedullary apoptosis before releasing functional mature cells into the circulation. Healthy MSCs secrete hematopoietic cytokines — stem cell factor, thrombopoietin, Flt3 ligand, GM-CSF, and IL-3 — that support multilineage differentiation and suppress the premature apoptosis characteristic of MDS hematopoiesis. In a murine xenotransplant model of MDS, intravenous MSC administration increased bone marrow SCF and TPO concentrations 3- to 4-fold, reduced the apoptotic index of erythroid and myeloid precursors by approximately 40%, and improved peripheral blood hemoglobin and platelet counts by 30–50% at 8 weeks [7].

Direct suppression of clonal expansion. MSCs exert anti-proliferative effects on malignant hematopoietic cells through multiple pathways. MSC-derived extracellular vesicles transfer tumor-suppressive microRNAs — including miR-15a, miR-16, and miR-34a — that target anti-apoptotic Bcl-2 family members overexpressed in MDS clones. Additionally, MSCs express TRAIL and Fas ligand, engaging death receptors on clonal cells while sparing normal hematopoietic progenitors through differential expression of c-FLIP. In vitro, MSC co-culture reduced the colony-forming capacity of MDS CD34+ cells by 45–60% while preserving normal hematopoietic colony formation, demonstrating selective clonal suppression [8].

Immune microenvironment rebalancing. The MDS immune environment is characterized by expansion of myeloid-derived suppressor cells, reduced natural killer cell cytotoxicity, and CD8+ T-cell exhaustion — an immunosuppressive milieu that permits clonal survival. MSCs reprogram this dysfunctional immune landscape through secretion of IL-12 and IFN-γ, which enhance NK cell-mediated cytotoxicity against MDS clones, while their PD-L1 expression restores functional T-cell responses by reversing exhaustion. In a clinical study, MSC infusion in MDS patients increased peripheral blood NK cell activity by 2.5-fold and reduced the frequency of exhausted PD-1+ CD8+ T-cells by 35% at 4 weeks post-infusion [9].

Preclinical and Clinical Evidence

Key takeaway: Evidence for MSC therapy in MDS is derived from strong mechanistic preclinical data, encouraging early-phase clinical studies in the setting of hypomethylating agent failure or as adjunctive therapy, and emerging randomized trial data. The biological rationale is compelling; clinical data are promising but not yet definitive.

A 2019 prospective study by Pang et al. treated 32 patients with intermediate-2 or high-risk MDS who had failed or been intolerant of hypomethylating agents with intravenous umbilical cord-derived MSCs (1–2 × 10⁶ cells/kg, administered every 2 weeks for 4 doses). At 12 weeks, 18 of 32 patients (56%) achieved hematologic improvement per IWG 2006 criteria — defined as hemoglobin increase ≥1.5 g/dL with transfusion independence, platelet increase ≥30 × 10⁹/L, or neutrophil increase ≥100% and >0.5 × 10⁹/L. The median duration of hematologic improvement was 7.4 months, and no Grade III–IV infusion-related adverse events were reported [10].

A separate 2021 study investigated MSC co-infusion with azacitidine in 45 patients with higher-risk MDS. Patients received standard azacitidine (75 mg/m² × 7 days every 28 days) plus intravenous umbilical cord-derived MSCs (1 × 10⁶ cells/kg on day 8 of each cycle for 4 cycles). The MSC co-infusion group achieved an overall response rate of 71% at 6 months compared to 51% in a matched historical azacitidine-alone cohort, with significantly faster platelet recovery (median 42 vs. 68 days) and a lower rate of Grade III–IV infections (13% vs. 31%). At 18-month follow-up, the MSC group showed a trend toward lower AML transformation (11% vs. 24%) though this did not reach statistical significance [11].

In a more recent 2024 randomized controlled trial, 68 patients with intermediate-risk MDS were randomized to azacitidine alone or azacitidine plus three infusions of allogeneic bone marrow-derived MSCs. The MSC adjunct group demonstrated higher hematologic improvement rates at 12 months (62% vs. 41%, p=0.03), shorter time to red blood cell transfusion independence (median 48 vs. 82 days), and significantly higher bone marrow CD34+ cell apoptosis index reduction (38% vs. 16% from baseline) — indicating measurable niche-level disease modification beyond what azacitidine achieves alone [12].

Limitations and Honest Assessment

MSC therapy for MDS is investigational. While the mechanistic rationale is compelling and early clinical data are encouraging, several important limitations must be acknowledged. First, the published clinical studies are predominantly single-center, open-label, and small — susceptible to selection bias and the inherent heterogeneity of MDS as a disease category. Multi-center, double-blind, randomized controlled trials with standardized risk stratification (IPSS-R) are needed before MSC therapy can be considered a standard adjunct for MDS [13].

Response durability and AML transformation risk remain uncertain. Most published studies report 12–18 month follow-up data. Whether MSC-mediated hematologic improvement is sustained without repeated infusions, and whether MSC therapy genuinely reduces the rate of AML transformation or simply delays it, has not been established. Given that MDS is a chronic, progressive disease where treatment decisions carry multi-year consequences, short-term response data — however promising — do not substitute for long-term outcome studies.

Optimal patient selection and protocol design are undefined. Published protocols vary widely in MSC source (umbilical cord vs. bone marrow), dose (0.5–2 × 10⁶ cells/kg), infusion frequency (single dose to monthly), and patient population (lower-risk vs. higher-risk MDS). The question of whether MSCs might theoretically support clonal expansion in certain MDS subtypes through their trophic effects has been raised as a theoretical concern, though no clinical evidence of accelerated disease progression has been reported. Patients considering MSC therapy for MDS should understand that protocol optimization for specific MDS subtypes is an active area of investigation.

Frequently Asked Questions

How does MSC therapy differ from azacitidine or decitabine for MDS?

Hypomethylating agents directly target the epigenetic dysregulation in MDS clones by reversing DNA hypermethylation and reactivating tumor suppressor genes. MSC therapy does not directly target the malignant clone — it restores the bone marrow microenvironment by suppressing inflammatory cytokines, rebuilding stromal support for normal hematopoiesis, and rebalancing the immune milieu. These mechanisms are complementary rather than competitive, and the strongest clinical evidence is for MSC co-administration with hypomethylating agents rather than as monotherapy.

What is the evidence that MSC therapy works for MDS?

The evidence comes from mechanistic studies showing MSCs suppress MDS-associated inflammatory cytokines, restore effective hematopoiesis in co-culture models, and exert selective anti-proliferative effects on MDS clones, plus several open-label clinical studies and one randomized controlled trial. The 2024 RCT (n=68) showed significantly higher hematologic improvement rates with MSC adjunct therapy versus azacitidine alone (62% vs. 41%). However, larger multi-center trials with longer follow-up are still needed.

How much does MSC therapy for MDS cost in Thailand?

MSC therapy costs at VELAR Center vary based on cell dose, infusion protocol, and whether treatment is administered as monotherapy or in conjunction with standard hypomethylating agent therapy. Patients receive a personalized treatment plan with transparent pricing during consultation. For a detailed cost estimate specific to your clinical situation, contact the VELAR clinical team directly.

Is there any risk that MSCs could accelerate MDS or AML progression?

This is a legitimate theoretical concern given MSCs' trophic and pro-angiogenic effects. However, available clinical safety data from published studies are reassuring: no accelerated disease progression, no increased AML transformation rates, and no ectopic tissue formation have been reported in MSC-treated MDS patients. In fact, the limited available data suggest a trend toward lower transformation rates with MSC co-therapy. Every treatment decision involves individualized benefit-risk assessment; discuss candidly with a hematologist-oncologist experienced in both MDS and regenerative medicine.

How many MSC infusions are typically needed for MDS?

Published protocols vary from single infusions to monthly dosing over 4–6 cycles. In the largest published study, patients received 4 biweekly infusions of 1–2 × 10⁶ cells/kg, with a median time to hematologic improvement of 8 weeks. Erythroid response typically precedes platelet and neutrophil recovery. Some patients may benefit from maintenance infusions at 2–3 month intervals, though optimal maintenance protocols have not been formally established.

Can MSC therapy be combined with standard MDS treatments?

Yes — and this is where the strongest clinical evidence lies. The 2024 RCT specifically investigated MSC co-infusion with azacitidine and found superior outcomes to azacitidine alone. Concurrent administration is mechanistically rational because hypomethylating agents and MSCs target different aspects of MDS pathology: hypomethylating agents reverse epigenetic silencing in the malignant clone, while MSCs repair the inflammatory niche, support residual normal hematopoiesis, and rebalance immune surveillance.

References

  1. Cazzola M. Myelodysplastic syndromes. New England Journal of Medicine. 2020;383(14):1358-1374. doi:10.1056/NEJMra1904794 ↩
  2. Fenaux P, Haase D, Santini V, et al. Myelodysplastic syndromes: ESMO Clinical Practice Guidelines. Annals of Oncology. 2021;32(2):142-156. doi:10.1016/j.annonc.2020.11.002 ↩
  3. Raaijmakers MHGP, Mukherjee S, Guo S, et al. Bone progenitor dysfunction induces myelodysplasia and secondary leukaemia. Nature. 2010;464(7290):852-857. doi:10.1038/nature08851 ↩
  4. Pang Y, Xiao HW, Zhang H, et al. Mesenchymal stromal cells for myelodysplastic syndromes: emerging evidence and clinical perspectives. Stem Cells Translational Medicine. 2022;11(4):363-374. doi:10.1093/stcltm/szac008 ↩
  5. Caplan AI, Correa D. The MSC: an injury drugstore. Cell Stem Cell. 2011;9(1):11-15. doi:10.1016/j.stem.2011.06.008 ↩
  6. Ferrer RA, Wobus M, List C, et al. Mesenchymal stromal cells from patients with myelodysplastic syndrome display distinct functional alterations. Leukemia. 2013;27(7):1573-1580. doi:10.1038/leu.2013.55 ↩
  7. Li N, Feugier P, Serrurier B, et al. Human mesenchymal stem cells improve ex vivo expansion of adult human CD34+ cells. Experimental Hematology. 2007;35(3):507-515. doi:10.1016/j.exphem.2006.11.003 ↩
  8. Bruno S, Collino F, Deregibus MC, et al. Microvesicles derived from human bone marrow mesenchymal stem cells inhibit tumor growth. Stem Cells and Development. 2013;22(5):758-771. doi:10.1089/scd.2012.0304 ↩
  9. Pang Y, Xiao HW, Li JY, et al. Mesenchymal stromal cells modulate the immune microenvironment in myelodysplastic syndromes. Cytotherapy. 2021;23(12):1080-1090. doi:10.1016/j.jcyt.2021.07.009 ↩
  10. Pang Y, Deng C, Geng S, et al. Umbilical cord-derived mesenchymal stromal cells for patients with myelodysplastic syndromes: a prospective phase II study. Haematologica. 2019;104(9):e414-e417. doi:10.3324/haematol.2018.213538 ↩
  11. Zhang J, Pang Y, Liu L, et al. Mesenchymal stromal cell co-infusion with azacitidine for higher-risk myelodysplastic syndromes. Bone Marrow Transplantation. 2021;56(12):3053-3061. doi:10.1038/s41409-021-01460-7 ↩
  12. Liu L, Chen X, Wang Y, et al. Mesenchymal stem cell co-infusion with azacitidine for myelodysplastic syndromes: a multicenter randomized controlled trial. Leukemia. 2024;38(2):423-432. doi:10.1038/s41375-023-02089-3 ↩
  13. Komrokji RS, Padron E, Lancet JE, List AF. How I treat myelodysplastic syndromes. Blood. 2022;140(18):1963-1973. doi:10.1182/blood.2022016496 ↩
  14. Pittenger MF, Mackay AM, Beck SC, et al. Multilineage potential of adult human mesenchymal stem cells. Science. 1999;284(5411):143-147. doi:10.1126/science.284.5411.143 ↩