Key Highlights

• The FDA approved the T-cell Proliferation Inhibition BioAssay for Ryoncil.

• TIBA can be used for commercial batch release and stability monitoring.

• The assay joins two existing potency tests used for the cell therapy.

• Ryoncil recorded US$115.2mn in net sales for FY26.

Mesoblast (ASX:MSB) added another regulatory piece to Ryoncil's commercial Manufacturing framework after the US Food and Drug Administration approved its T-cell Proliferation Inhibition BioAssay (TIBA). Announced on 24 September 2026, the new potency assay was cleared for commercial batch release and stability monitoring, expanding the testing framework used to assess the cell therapy as production and development activities progressed.

The new test is called the T-cell Proliferation Inhibition BioAssay, or TIBA. Mesoblast says the FDA has cleared it for both batch release and stability monitoring of commercial product.

What a potency assay actually does

A conventional drug is a defined chemical that can be checked tablet by tablet.

Living cell therapies are much harder to pin down. Ryoncil is made from mesenchymal stromal cells (MSCs) derived from donor bone marrow, grown in culture, frozen and shipped as an off-the-shelf product. Two batches can look the same under a microscope and still behave differently in the body.

A potency assay tries to close that gap. It is a lab test that measures whether a batch has the biological activity the product relies on. In Ryoncil's case, the FDA's review documents describe release assays that measure the immunomodulatory activity of the cells. Put simply, that is their ability to calm an overactive immune response.

This matters because Ryoncil is approved for steroid-refractory acute graft-versus-host disease (SR-aGvHD) in patients aged two months and older. That is a condition in which donor immune cells from a transplant attack the recipient's body. The TIBA name suggests what it checks: whether the cells can hold back T-cell proliferation, which is part of the immune activity involved in GvHD.

Every batch must pass its release tests before sale, so potency assays act as a gate between factory and patient.

Why a third test matters

According to Mesoblast, TIBA will not replace the existing tests. It joins a "matrix" with two potency assays already in use: one measuring IL-2Rα inhibition and another the company calls CAP (Cell Adhesion and Proliferation).

The key selling point is sensitivity. Mesoblast says TIBA can pick up shifts in potency that could arise from changes to the manufacturing process or from making the product in new facilities.

That is where the FDA's own paperwork gets interesting. When the agency approved Ryoncil in December 2024, its review summary warned that the two original release assays might not be enough to show comparability after future manufacturing changes. The FDA recorded a post-marketing commitment for Mesoblast to develop and validate an additional, stability-indicating potency assay. The final report was due by 31 December 2027.

Mesoblast's announcement does not say outright that TIBA satisfies that commitment. Even so, the description lines up closely with what regulators asked for, and the approval has arrived more than a year ahead of the 2027 deadline.

The commercial angle: Supply and scale

Commercially, this is about flexibility.

Growing Demand usually means bigger runs, process tweaks or extra sites. For a cell therapy, each change invites the regulator's question: is the product still the same?

A more sensitive, FDA-approved test gives Mesoblast a better way to answer that question with data. The announcement does not promise faster approvals for future changes, but having the tool approved removes one piece of the puzzle.

Demand is clearly growing. Ryoncil was approved on 18 December 2024 as the first FDA-approved MSC therapy. In February 2025 Mesoblast set a US list price of US$194,000 per infusion, which comes to about US$1.55 million for a full eight-infusion course.

In its full-year results for the period to 30 June 2026, Mesoblast reported net Ryoncil sales of US$115.2 million, up from US$11.3 million the year before. Total Revenue was US$120.3 million. The company said it had onboarded more than 50 US transplant sites since launch, including 14 of the 15 largest, and that payer coverage had reached more than 280 million covered lives.

Label expansion and the pipeline

If that expansion succeeds, Mesoblast will need far more product. A potency framework designed to cope with process changes and new facilities is the kind of groundwork a larger launch would require. The announcement itself does not directly link TIBA to the adult programme.

Remestemcel-L is also being studied in biologic-resistant inflammatory bowel disease. Mesoblast's second-generation product, rexlemestrocel-L, is in development for heart failure and chronic low back pain. The company expects top-line Phase 3 back pain results in mid-calendar 2027.

Risks to Consider

A new quality test is not a new approval for a disease. It does not widen Ryoncil's label, and it does not guarantee future sales.