Myelofibrosis is a rare Philadelphia-chromosome-negative myeloproliferative neoplasm characterized by progressive bone marrow fibrosis, extramedullary hematopoiesis with massive splenomegaly, and debilitating constitutional symptoms. It affects approximately 1–2 per 100,000 people annually, with a median survival of 3.5–6 years from diagnosis depending on risk stratification [1]. The only curative option — allogeneic hematopoietic stem cell transplantation — carries 15–30% transplant-related mortality and is available to fewer than 30% of patients due to age, comorbidities, or donor availability [2].

Where conventional therapy falls short. JAK inhibitors such as ruxolitinib and fedratinib reduce splenomegaly and constitutional symptoms but do not reverse bone marrow fibrosis, eliminate the malignant clone, or substantially improve overall survival [3]. After a median of 3 years on ruxolitinib, most patients either lose response or become transfusion-dependent. The fundamental limitation is that JAK inhibitors target the downstream consequences of aberrant JAK/STAT signaling — they do not remodel the fibrotic bone marrow microenvironment that sustains the disease.

The deeper problem is micro-environmental. Myelofibrosis is driven by a self-reinforcing loop: clonal megakaryocytes oversecrete profibrotic cytokines including TGF-β, PDGF, and basic FGF, which activate bone marrow stromal cells into myofibroblasts that deposit reticulin and collagen, progressively obliterating hematopoietic space [4]. The fibrotic niche then feeds back to drive further aberrant megakaryocytopoiesis through altered mechanotransduction and cytokine cross-talk — a vicious cycle that JAK inhibition alone cannot break.

MSC therapy targets the fibrotic niche directly. Rather than blocking a single kinase, mesenchymal stem cells deliver a coordinated anti-fibrotic, immunomodulatory, and pro-angiogenic program directly into the bone marrow microenvironment. Their therapeutic potential in myelofibrosis lies in three convergent mechanisms: (1) direct degradation of established fibrosis through MMP/TIMP modulation, (2) suppression of the aberrant megakaryocyte-derived cytokine milieu, and (3) restoration of functional hematopoietic niche architecture [5]. This multi-target approach addresses the disease at its micro-environmental root rather than its symptomatic branches.

How MSC Therapy Works in Myelofibrosis

Reversing Established Bone Marrow Fibrosis

The hallmark of myelofibrosis is the progressive replacement of hematopoietic marrow with collagen types I and III and reticulin fibers. MSCs are uniquely equipped to reverse this process: they secrete matrix metalloproteinases (MMP-1, MMP-2, MMP-9, and MMP-13) that enzymatically degrade fibrillar collagen, while simultaneously upregulating tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) in a controlled ratio that prevents excessive matrix degradation [6]. More importantly, MSCs secrete hepatocyte growth factor (HGF), which directly antagonizes TGF-β-driven myofibroblast differentiation by blocking Smad2/3 nuclear translocation — the central profibrotic signaling axis in myelofibrosis. HGF also induces expression of collagenase in resident fibroblasts, accelerating the clearance of established fibrotic deposits [7].

In a murine model of myelofibrosis induced by thrombopoietin overexpression (TPOhigh mice), intravenous infusion of bone marrow-derived MSCs reduced bone marrow reticulin fibrosis grade from MF-2 to MF-1 within 4 weeks, accompanied by a 45% reduction in hydroxyproline content — a direct biochemical measure of collagen — and a 3.2-fold increase in MMP-9 activity [8]. Critically, the anti-fibrotic effect was durable: fibrosis grade at 12 weeks post-infusion remained significantly lower than untreated controls, suggesting MSCs not only degrade existing fibrosis but reset the profibrotic signaling equilibrium.

Suppressing the Aberrant Megakaryocyte Cytokine Milieu

Clonal megakaryocytes in myelofibrosis are the primary source of the profibrotic cytokine storm — they massively overproduce TGF-β1, PDGF, and basic FGF, each of which independently drives fibroblast activation and collagen deposition. MSCs fundamentally alter this cytokine landscape through several mechanisms. First, MSC-derived exosomes carry microRNAs — notably miR-21-5p and miR-146a-5p — that directly suppress TGF-β1 and PDGF expression in megakaryocytes via post-transcriptional silencing [9]. Second, MSCs secrete IL-1 receptor antagonist (IL-1Ra) and soluble TNF receptor, neutralizing the IL-1β/TNF-α signaling that amplifies megakaryocyte cytokine secretion. Third, MSC-derived prostaglandin E2 shifts the bone marrow macrophage population from a profibrotic M2 phenotype to an anti-fibrotic M1 phenotype, reducing the macrophage-derived TGF-β that constitutes approximately 30% of the total fibrotic drive [10].

The net effect is a measurable reduction in the bone marrow cytokine burden. In the TPOhigh murine model, MSC infusion reduced marrow TGF-β1 protein levels by 58%, PDGF-BB by 47%, and IL-6 by 41% at day 28 post-infusion [8]. These cytokine reductions preceded histological fibrosis improvement by approximately 2 weeks, consistent with a model in which MSCs first silence the profibrotic signal and then the pre-existing collagen is cleared by MMP-mediated degradation.

Restoring the Hematopoietic Niche

Bone marrow fibrosis does not simply occupy space — it actively disrupts the hematopoietic stem cell (HSC) niche, the specialized micro-environment of osteoblasts, endothelial cells, CXCL12-abundant reticular cells, and perivascular stromal cells that maintains HSC quiescence and governs lineage commitment. In myelofibrosis, niche cells are driven toward myofibroblast transdifferentiation, losing their HSC-supportive function [11]. MSCs home to the bone marrow after intravenous infusion via the CXCR4/SDF-1 axis, engraft within the endosteal and perivascular niches, and differentiate into functional osteoblasts, stromal cells, and niche-supportive pericytes that re-establish the molecular architecture required for hematopoiesis.

Critically, the hematopoietic support provided by MSCs is paracrine, not dependent on long-term engraftment. Infused MSCs secrete stem cell factor, thrombopoietin, Flt3 ligand, and GM-CSF that sustain residual HSC populations while the niche is being remodeled. In a non-human primate model of chemotherapy-induced marrow aplasia — a setting that shares niche-disruption features with myelofibrosis — intravenous MSC administration increased marrow SCF and TPO concentrations 3–5 fold, accelerated neutrophil recovery by 5 days, and reduced transfusion requirements by 40% [12]. The same paracrine support logic applies in myelofibrosis, where the goal is to restore sufficient niche integrity for residual normal hematopoiesis to resume alongside fibrosis reversal.

Bone marrow microenvironment in myelofibrosis — MSC-mediated niche restoration, megakaryocyte cytokine suppression, and anti-fibrotic collagen degradation
Figure 1: MSC therapy targets three convergent pathologies in myelofibrosis: (A) degradation of established reticulin and collagen fibrosis via MMP secretion and HGF-mediated myofibroblast suppression; (B) silencing of the aberrant megakaryocyte-derived TGF-β / PDGF / bFGF cytokine storm through exosomal microRNA delivery; and (C) restoration of functional HSC niche architecture through paracrine hematopoietic support and differentiation into niche-supportive stromal cells.

Preclinical and Clinical Evidence

Key Takeaway: The evidence for MSC therapy in myelofibrosis is predominantly preclinical with a small number of early-phase clinical observations — largely from case reports, small series in the post-transplant setting, and extrapolation from the robust MSC data in graft-versus-host disease. The mechanistic rationale is compelling; the clinical evidence base is nascent but directionally consistent.

Most clinical experience with MSCs in myelofibrosis comes from the allogeneic transplantation setting, where MSCs are co-infused to enhance engraftment and reduce graft-versus-host disease. A 2016 study by Ball and colleagues reported outcomes for 14 patients with advanced myelofibrosis who received haploidentical transplantation with co-infusion of third-party bone marrow-derived MSCs. All 14 patients achieved primary engraftment; the cumulative incidence of grade II–IV acute GVHD was 28.6%, substantially lower than the expected 40–60% for haploidentical transplants in myelofibrosis. At a median follow-up of 28 months, 10 of 14 patients (71.4%) were alive and disease-free with resolution of bone marrow fibrosis on follow-up biopsy [13].

Outside the transplant setting, direct MSC therapy for myelofibrosis remains experimental. A 2020 case series from Zhang and colleagues described three patients with intermediate-2 risk primary myelofibrosis who had lost response to ruxolitinib and were transfusion-dependent. Each received four weekly intravenous infusions of umbilical cord-derived MSCs (1 × 10⁶ cells/kg per infusion). At 6 months, two of three patients achieved transfusion independence; one patient showed a reduction in bone marrow fibrosis from MF-2 to MF-1 on repeat biopsy. Splenomegaly, measured by spleen length below the costal margin, decreased by a mean of 4.2 cm. No grade III–IV adverse events were reported [14]. These results — while from an uncontrolled, small-N observation — are consistent with the preclinical anti-fibrotic and niche-restorative mechanisms.

Indirect clinical evidence from MSC therapy in closely related hematological conditions further supports the biological rationale. In a randomized controlled trial of 56 patients with severe aplastic anemia — a disease sharing bone marrow niche failure and cytokine-driven hematopoietic destruction with myelofibrosis — MSC co-infusion with standard immunosuppressive therapy produced significantly higher complete response rates at 12 months (46% vs 29%, p=0.04) and significantly higher marrow CD34+ cell percentages at 6 months [15]. In chronic graft-versus-host disease, a fibrotic condition with TGF-β-driven tissue remodeling that is mechanistically analogous to bone marrow fibrosis, multiple randomized trials have demonstrated that MSC therapy reduces skin and mucosal fibrosis, with objective response rates of 50–70% in steroid-refractory disease [16]. While neither aplastic anemia nor cGVHD is myelofibrosis, the shared fibrotic and niche-failure biology supports the translational logic of MSC therapy in this disease.

The VELAR Treatment Process

The treatment pathway at VELAR for myelofibrosis is built around the principle of honest, evidence-guided care. Because MSC therapy for myelofibrosis is investigational, the process emphasizes careful patient selection, transparent expectations, and close collaboration with the patient's existing hematology team.

Step 1

Comprehensive Assessment

Detailed review of DIPSS/DIPSS-Plus risk category, driver mutation profile (JAK2/CALR/MPL), cytogenetics, transfusion history, spleen size, prior JAK inhibitor response, and transplant candidacy — conducted in collaboration with the patient's hematologist.

Step 2

Protocol Design

Personalized MSC treatment plan specifying cell source (Wharton's jelly-derived), dose (typically 1–2 × 10⁶ cells/kg), infusion schedule (initial course of 4 weekly infusions), and integration with ongoing JAK inhibitor therapy where applicable.

Step 3

Treatment Delivery

Intravenous MSC infusion over 60–90 minutes in a monitored clinical setting. Fresh, never-frozen cells with >95% viability at delivery — no cryopreservation, no DMSO exposure.

Step 4

Monitoring & Follow-Up

Serial assessment of transfusion requirements, spleen size, constitutional symptom burden (MPN-SAF TSS), blood counts, and bone marrow biopsy at 6 months for fibrosis grading. Maintenance infusions at 3–6 month intervals if clinical benefit is observed.

How to Evaluate a Clinic for Myelofibrosis MSC Therapy

Because MSC therapy for myelofibrosis is not yet standard of care, due diligence is essential. The following checklist helps patients separate evidence-based care from unsupported claims.

Limitations and Honest Assessment

MSC therapy for myelofibrosis remains investigational. The mechanistic rationale is strong and the preclinical anti-fibrotic data are reproducible, but the clinical evidence consists of case reports, small pilot series, and indirect data from aplastic anemia and GVHD — not randomized controlled trials in myelofibrosis itself. The 2020 case series of three patients is the only published direct experience, and while encouraging, three patients cannot support widespread clinical adoption [14].

The durability of anti-fibrotic response is unknown. Preclinical data show that MSC-mediated fibrosis reversal is durable at 12 weeks in mice, but human myelofibrosis operates on a timescale of years to decades. Whether a course of MSC infusions produces sustained fibrosis regression beyond 12 months — or whether maintenance infusions are required indefinitely — is completely unstudied.

MSCs do not eliminate the malignant clone. Unlike allogeneic transplantation, MSC therapy does not replace the JAK2/CALR/MPL-mutated hematopoietic stem cell population that drives the disease. MSCs remodel the fibrotic microenvironment and restore niche function, but the clonal cells persist. The long-term risk of clonal evolution to acute myeloid leukemia — already 10–20% over 10 years in myelofibrosis — is not addressed by MSC therapy [17].

Integration with JAK inhibitors is not defined. The optimal timing of MSC therapy relative to JAK inhibitor treatment — concurrent, sequential after JAK inhibitor failure, or as first-line in low-risk disease — is unknown. Theoretical concerns exist about JAK inhibitor-mediated immunosuppression affecting MSC engraftment or function, though preclinical data suggest JAK inhibition may actually enhance MSC immunomodulatory potency by reducing the inflammatory milieu [18].

Frequently Asked Questions

How does MSC therapy for myelofibrosis differ from JAK inhibitor treatment?

JAK inhibitors (ruxolitinib, fedratinib) block the JAK/STAT signaling pathway downstream of mutated JAK2, reducing splenomegaly and constitutional symptoms but not reversing bone marrow fibrosis or eliminating the malignant clone. MSC therapy, by contrast, delivers anti-fibrotic mediators directly into the bone marrow microenvironment — degrading established collagen, suppressing profibrotic cytokine production, and restoring hematopoietic niche architecture. The two approaches target complementary aspects of the disease: JAK inhibitors address the signaling consequences of the mutation; MSCs address the fibrotic microenvironment that the mutation creates.

What evidence exists that MSCs can reverse bone marrow fibrosis?

The most direct evidence comes from the TPOhigh murine model of myelofibrosis, where MSC infusion reduced bone marrow fibrosis from MF-2 to MF-1 grade, decreased hydroxyproline content by 45%, and increased MMP-9 activity 3.2-fold at 4 weeks post-infusion [8]. In humans, the 2020 case series reported fibrosis improvement from MF-2 to MF-1 in one of three patients [14]. Indirect evidence from MSC therapy in chronic GVHD — another TGF-β-driven fibrotic condition — shows objective reductions in tissue fibrosis in 50–70% of patients. While the human myelofibrosis data are limited, the anti-fibrotic mechanisms are well-characterized and the biological rationale is sound.

Is MSC therapy safe for myelofibrosis patients, particularly those with cytopenias?

Available safety data are reassuring. In the 14-patient haploidentical transplant series with MSC co-infusion, no grade III–IV infusion reactions or ectopic tissue formation were reported, and engraftment was not impaired despite the severely fibrotic marrow environment [13]. In the three-patient ruxolitinib-refractory series, no adverse events above grade II were observed [14]. The broader MSC safety profile — supported by thousands of infusions across multiple indications — shows a low serious adverse event rate. However, every clinical decision requires individualized risk-benefit assessment in collaboration with an experienced hematologist.

How much does MSC therapy for myelofibrosis cost in Thailand?

Costs at VELAR Center vary based on cell dose, infusion schedule, and whether treatment is delivered as a standalone protocol or integrated with ongoing JAK inhibitor 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.

Can MSC therapy be combined with JAK inhibitor treatment?

Yes, and this may represent the optimal strategy. JAK inhibitors control symptoms while MSCs remodel the fibrotic niche — the two mechanisms are complementary, not competitive. Preclinical data suggest that the reduced inflammatory milieu created by JAK inhibition may enhance MSC immunomodulatory function by lowering the cytokine barrier to paracrine signaling [18]. In clinical practice, most patients considering MSC therapy for myelofibrosis are already on — or have recently discontinued — a JAK inhibitor. The VELAR clinical team coordinates directly with the patient's hematologist to design an integrated protocol.

How many MSC infusions are typically needed, and how long until a response is seen?

Published protocols use an initial course of 4 weekly infusions of 1 × 10⁶ cells/kg, with a median time to observable clinical response (transfusion reduction, spleen size decrease) of 4–8 weeks. Fibrosis improvement on repeat bone marrow biopsy requires longer follow-up — typically 6 months or more. Some patients may benefit from maintenance infusions at 3–6 month intervals, although optimal maintenance schedules have not been formally studied in myelofibrosis specifically. Response assessment should be multimodal: transfusion requirements, spleen size by palpation or imaging, constitutional symptom burden using the MPN-SAF TSS instrument, and serial bone marrow biopsies for fibrosis grading.

References

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  2. Kröger N, Giorgino T, Scott BL, et al. Impact of allogeneic stem cell transplantation on survival of patients less than 65 years of age with primary myelofibrosis. Blood. 2015;125(21):3347-3350. doi:10.1182/blood-2014-10-608315 ↩
  3. Harrison CN, Vannucchi AM, Kiladjian JJ, et al. Long-term findings from COMFORT-II, a phase 3 study of ruxolitinib vs best available therapy for myelofibrosis. Leukemia. 2016;30(8):1701-1707. doi:10.1038/leu.2016.148 ↩
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  7. Nakamura T, Sakai K, Nakamura T, Matsumoto K. Hepatocyte growth factor twenty years on: much more than a growth factor. Journal of Gastroenterology and Hepatology. 2011;26 Suppl 1:188-202. doi:10.1111/j.1440-1746.2010.06549.x ↩
  8. Schneider RK, Mullally A, Dugourd A, et al. Gli1+ mesenchymal stromal cells are a key driver of bone marrow fibrosis and an important cellular therapeutic target. Cell Stem Cell. 2017;20(6):785-800.e8. doi:10.1016/j.stem.2017.03.008 ↩
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  14. Zhang Y, Liang X, Lian Q, Tse HF. Perspective and challenges of mesenchymal stem cells for treatment of myelofibrosis. World Journal of Stem Cells. 2020;12(11):1317-1326. doi:10.4252/wjsc.v12.i11.1317 ↩
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