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Two months after ExCellThera’s Zemcelpro (UM171 cell therapy) received a positive opinion from the European Medicines Agency’s Committee for Medicinal Products for Human Use (CHMP), the European Commission granted the therapy conditional marketing authorization for adult patients with blood cancers who need a stem cell transplant but lack a suitable donor.
The therapy combines cord blood–derived stem cells expanded ex vivo using UM171, a proprietary small molecule that promotes stem cell self-renewal, with unmodified cells from the same unit. Zemcelpro aims to increase transplant access in cases where no matched donor is available by making smaller cord blood units viable for use in adults.
With this approval in the bag, Zemcelpro becomes the first treatment of its kind in the European Union (EU), targeting the unresolved issue in transplant medicine: the challenge of donor availability, particularly in urgent cases or among patients with uncommon human leukocyte antigen (HLA) types.
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How ExCellThera’s Zemcelpro works
The therapy builds on cord blood, a long-standing but underused source of stem cells for adult transplants. The main issue has always been quantity: a single cord blood unit often doesn’t contain enough stem cells for a successful graft, especially in larger or older patients.
One of the key bottlenecks in blood stem cell transplantation is the lack of timely access to suitably matched donors. Some of these challenges are even more common in patients with rare HLA types, which is frequently the case among individuals from ethnic minority groups. While cord blood is more tolerant of HLA mismatch, its use in adults has been limited by insufficient cell doses for reliable engraftment.
Zemcelpro addresses this by using UM171, a small molecule designed to expand the number of stem cells while keeping them functionally intact. The expanded product contains two components: CD34+ cells that have been grown with UM171, and unmodified CD34 cells, both taken from the same cord blood unit. According to ExCellThera, UM171 helps the stem cells preserve their ability to self-renew and engraft effectively, while also improving what the company calls their “metabolic fitness.”
According to ExCellThera, UM171 not only drives stem cell expansion but also enhances the metabolic fitness of blood stem cells by reducing oxidative stress and preserving mitochondrial function. In practice, this means the expanded cells maintain their ability to self-renew, home to the bone marrow, and engraft efficiently. “This improved cellular resilience is critical for transplant outcomes, as it contributes to durable engraftment, lowers the risk of graft failure, and may reduce complications associated with delayed immune recovery,” a company spokesperson explained.
The result is a cryopreserved, off-the-shelf graft that makes smaller cord blood units viable for adult patients. That could open the door to transplants for people who previously had no good donor options, not by finding more donors, but by making better use of what’s already in the freezer.
The cord blood expansion field: limited competition, big opportunity
Cord blood expansion therapy isn’t the most competitive market. That said, Zemcelpro won’t be the first to be approved worldwide. Indeed, Gamida Cell’s Omidubicel was approved in the U.S. in 2023.
Omidubicel, developed by Gamida Cell, uses nicotinamide to expand progenitor cells from cord blood. It focuses on early immune recovery and lowering infection risk, helping cord blood regain traction as a viable graft source. According to ExCellThera, while Zemcelpro and Omidubicel both use ex vivo expansion of stem cells, they differ in their underlying technologies and clinical outcomes.
“Omidubicel expands mainly progenitor cells using nicotinamide, a derivative of vitamin B, improving time to neutrophil recovery. In contrast, Zemcelpro is derived from UM171, a proprietary small molecule, which expands long-term stem cells while enhancing their metabolic fitness and self-renewal capacity. This may contribute to more sustained, multilineage engraftment and long-term hematopoietic reconstitution.”
“The key differentiator is UM171’s ability to amplify a more primitive stem cell population, potentially translating into more durable long-term clinical benefits. Because of this, Zemcelpro can amplify cord blood units that are normally too small for clinical use, a feature not possible with omidubicel,” said an ExCellThera spokesperson.
Beyond Zemcelpro and Omidubicel, a handful of other cord blood expansion strategies have been explored over the past decade, including aryl hydrocarbon receptor antagonists like StemRegenin‑1 (SR‑1) and Notch ligand–based systems. While some of these showed early promise in boosting cell yield or accelerating neutrophil recovery, most have not progressed to late-stage clinical trials. In some cases, development appears to have stalled entirely, with no major updates or active studies reported in recent years.
This lack of momentum has left the field with few serious contenders. Zemcelpro becomes only the second product of its kind to reach the market, and the first in Europe. That timing could offer ExCellThera a significant head start in capturing a niche but clinically meaningful segment of the transplant space.
What’s next for ExCellThera
While the therapy received conditional approval today, the timing of access will depend on the different jurisdictions within Europe. “The timing of Zemcelpro availability in individual countries will depend on several factors, including the completion of national reimbursement procedures. In the meantime, Cordex Biologics (a subsidiary of ExCellThera) will be working closely with national health authorities to enable early access for eligible patients ahead of the reimbursement process, whenever possible,” said Jean Proulx, vice president of Global Medical Affairs and Access at ExCellThera.
ExCellThera is also preparing filings in key jurisdictions, including the U.S., where a phase 3 trial is already underway in additional indications. “We believe this product has the potential to be a best-in-class treatment option for high-risk leukemias and myelodysplasias, where unmet medical needs persist despite the standard-of-care transplant, due to its compelling combined efficacy and safety profile. We look forward to advancing this therapy into a multinational registrational phase 3 trial, including U.S. sites, for patients with high and very-high-risk leukemias and myelodysplasias,” said David Millette, the company’s CEO.
Beyond regulatory momentum, pediatric and non-malignant blood disorder indications are actively being explored. This indicates the start of a broader push to position UM171 as a versatile platform technology.
That platform potential is evident in ExCellThera’s Enhance program, which leverages UM171 not just for cord blood expansion but also to improve gene-modified stem cells and CAR-T cell products.
UM171’s ability to expand and enhance the quality of hematopoietic stem cells makes it a valuable tool across diverse cell and gene therapies. By increasing stem cell yield and metabolic fitness, UM171 can improve the efficiency of gene editing, CAR-T manufacturing, and other regenerative medicine approaches that depend on durable stem cell populations. Indeed, Millette encouraged anyone interested in using UM171 to reach out to ExCellThera, suggesting the company is definitely open for collaborations.
If UM171 successfully powers multiple downstream therapies, ExCellThera could emerge from its niche transplant role to become a partner for wider cell and gene therapy development, potentially making its EU transplant approval the first chapter in a larger story.
