Two-year safety outcomes of iPS cell-derived mesenchymal stromal cells in acute steroid-resistant graft-versus-host disease

Steroid-resistant acute graft-versus-host disease (SR-aGvHD) remains a life-threatening complication after allogeneic hematopoietic stem cell transplantation. While donor-derived mesenchymal stromal cells (MSCs) have immunomodulatory potential, clinical efficacy in GvHD has been inconsistent, in part due to scalability constraints, extensive ex vivo expansion, and substantial inter-donor and tissue-source variability that affect MSC function and potency. iPS cell-derived MSCs offer a theoretically scalable, consistent alternative that may reduce manufacturing heterogeneity and avoid replicative senescence. This study reports 2-year safety and outcome data from the first completed human clinical trial using iPS cell-derived MSCs (CYP-001) in adults with SR-aGvHD, extending prior 100-day results.

Prior work highlights key limitations of conventional donor-derived MSCs: low initial cell yields necessitating extensive passaging that can induce functional changes and senescence; and high inter-donor variability affecting responsiveness to inflammatory cytokines (IFN-γ, TNF) and indoleamine 2,3-dioxygenase expression, as well as gene expression, proliferation, and colony-forming capacity (refs 2,5–8). iPS cells, capable of indefinite self-renewal and pluripotency (refs 9–11), enable platform manufacturing (Cymerus) of consistent, allogeneic MSCs from a single donor-derived iPSC bank under GMP, xenogen/serum/feeder-free conditions with controls to minimize residual undifferentiated cells and teratoma risk (ref 12). Comparative outcomes in SR-aGvHD from literature: MSC products from other tissue sources show 2-year overall survival (OS) of 0–40% (refs 13–19). Ruxolitinib, approved for SR-aGvHD, demonstrated 18-month OS ~38% vs 36% for best available therapy in a phase III trial; 2-year OS not evaluable (ref 21). Real-world bone marrow-derived MSC use in ruxolitinib-refractory adults reported OS at 6, 12, and 24 months of 47% (38–56%), 35% (27–44%), and 30% (22–39%), respectively (ref 22).

Design: Phase I, multicenter, open-label, dose-escalation clinical trial of iPSC-derived MSCs (CYP-001) in adults with SR-aGvHD after allogeneic HSCT, conducted across seven centers in the UK and Australia (ClinicalTrials.gov NCT02923375). Conducted per ICH-GCP, local regulations, and the Declaration of Helsinki (2013). Ethics approval obtained in the UK (North East–York REC, 16/NE/0316) and Australia (Royal Adelaide Hospital HREC, HREC/16/RAH/412). Written informed consent required. Participants: Adults diagnosed with grade II–IV aGvHD who were steroid-resistant per investigator judgment, defined as failure to respond or progression after ≥3 days of steroids at ≥1 mg/kg/day. One consented individual withdrew pre-infusion due to myocardial infarction; 15 participants received study treatment. Intervention: CYP-001 administered intravenously on day 0 and day 7. Cohort A (n=8): 1×10^6 cells/kg per infusion (max 1×10^8 cells). Cohort B (n=7): 2×10^6 cells/kg per infusion (max 2×10^8 cells). All participants continued standard-of-care aGvHD therapies; no other investigational agents allowed until ≥28 days after first CYP-001 dose. Assessments: Primary evaluation period through day 100 after first infusion previously reported. This report covers extended follow-up to 24 months post-initial infusion with visits at 6, 12, 18, and 24 months, assessing survival status, GvHD grade (acute/chronic), additional GvHD treatments, malignancy status, and adverse events. Safety endpoints included serious adverse events (including death) and malignancy. Data management and analysis: Data collected in ClinCapture v2.1.15.15 Rev. 3743; analyses performed with SAS v9.4. Kaplan–Meier survival curve generated using GraphPad Prism 10. Manufacturing: CYP-001 derived via the Cymerus iPSC platform enabling large-scale, donor-independent manufacture under GMP, xenogen-/serum-/feeder-free conditions with quality controls to ensure absence of residual undifferentiated iPSCs.

- Safety: No serious adverse events, tumors, or other safety concerns were considered related to CYP-001 during the 2-year follow-up. - Survival: 9/15 participants (60%) survived at 24 months. Two deaths occurred during the day-100 primary period and four during the extended follow-up. Causes of death (none considered related to CYP-001): relapse of preexisting malignancy (n=2), pneumonia (n=2), GvHD (n=1), sepsis/multi-organ dysfunction (n=1). - Kaplan–Meier: Survival curve presented; letters indicate causes of death (G, P, S, R). - GvHD outcomes over follow-up (Table 1): - Survival: 6 mo 11/15 (73%); 12 mo 9/15 (60%); 18 mo 9/15 (60%); 24 mo 9/15 (60%). - No GvHD among survivors: 6 mo 8/11 (73%); 12 mo 6/9 (67%); 18 mo 7/9 (78%); 24 mo 6/9 (67%). - aGvHD grades at 6 mo among survivors: Grade I 2/11 (18%); Grade II 1/11 (9%); Grades III–IV 0. No aGvHD at ≥12 months. - cGvHD among survivors: 12 mo 3/9 (33%); 18 mo 2/9 (22%); 24 mo 3/9 (33%). Those with cGvHD received additional therapies (e.g., corticosteroids, calcineurin inhibitors, kinase inhibitors, mycophenolate mofetil, extracorporeal photopheresis). - Previously reported day-100 efficacy (context): complete response 53%, overall response 87% (from the initial trial report).

The 2-year follow-up demonstrates that systemically administered iPSC-derived MSCs (CYP-001) were safe and well tolerated, with a 2-year overall survival of 60% in adults with SR-aGvHD. These outcomes, if replicated in larger controlled studies, compare favorably with prior reports using donor-derived MSCs where 2-year OS often ranged from 0% to 40%, and with ruxolitinib where 18-month OS was 38% versus 36% for best available therapy and 2-year OS was not evaluable. Real-world outcomes in ruxolitinib-refractory adults treated with bone marrow-derived MSCs reported lower OS at 24 months (~30%). The absence of treatment-related serious adverse events, tumors, or other safety signals over 24 months supports the long-term safety of iPSC-derived MSCs. The results address key concerns about manufacturing consistency and scalability by leveraging an iPSC platform designed to minimize inter-donor variability and extensive passaging, thereby potentially enabling more reliable clinical performance in GvHD and other indications.

Systemic infusion of iPSC-derived MSCs (CYP-001) in adults with SR-aGvHD was safe and well tolerated, with sustained clinical outcomes through 24 months and a 2-year overall survival of 60%. These data, together with favorable safety, support continued development of iPSC-derived MSC therapies as a scalable and consistent alternative to donor-derived MSCs. A global phase II clinical trial in aGvHD (NCT05643638) commenced in 2023 to further evaluate efficacy and safety in a larger cohort.

This was a small, phase I, multicenter, open-label, nonrandomized study (n=15 treated) without a control arm, limiting causal inference and generalizability. Comparisons to outcomes from other trials are indirect and confounded by differences in populations, concomitant therapies, and study designs; authors caution against cross-trial comparisons. Standard-of-care treatments continued and additional GvHD treatments during follow-up (including for cGvHD) may confound attribution of long-term outcomes. The cohort lacked racial/ethnic diversity (all participants white in the original trial report), and the study was not powered for subgroup analyses. Follow-up was limited to 24 months, and rare late adverse events may not have been detected.