Mesoblast (ASX:MSB) hits 300 patients in the trial that could dwarf Ryoncil

A US$10bn indication now sits inside a 12-month readout window with FDA priority review locked in

Mesoblast (ASX:MSB) has just finished enrolling the pivotal Phase 3 trial that most investors have quietly been building their long-term thesis around. The MSB-DR004 study of rexlemestrocel-L for chronic low back pain has now treated at least 300 patients, meaning the trial is fully powered and the clock is officially running on a mid-CY2027 top-line readout.

For a company that spent most of the last decade being defined by regulatory setbacks, this is a genuinely different moment. Ryoncil finally cleared the FDA and is now scaling into a real commercial product. But the market has always understood that the much larger prize sits in back pain, not paediatric graft versus host disease.

That larger prize is what enrolment completion now brings into focus. Management flagged peak year revenue potential above US$10 billion at single-digit market penetration, targeting a US patient population of more than 7 million. Commercial manufacturing is already running in parallel to trial follow-up, which tells us how the company is thinking about the timeline from readout to filing.

The question for investors is no longer whether the trial will complete. It is whether the earlier MSB-DR003 efficacy signal holds up in a fully powered confirmatory study.

Why the back pain indication changes the whole valuation frame

Ryoncil is a real business, but it addresses roughly 400 paediatric patients a year in the US. Even with strong pricing and margin, it is a niche asset. The Q1 FY26 run-rate of US$19.1m in net sales, followed by December quarter guidance above US$30m gross, confirms the ramp is real but also confirms the ceiling.

Rexlemestrocel-L in chronic low back pain is a completely different animal. Discogenic back pain drives around 50% of US prescription opioid usage, and the current treatment options are steroid injections, surgery, or more opioids. A single intra-discal injection that produces durable pain reduction would slot into a market with essentially no direct competitor at the biologic tier.

We think this is the indication that justifies the current market cap on its own if the readout lands. Everything else, including Ryoncil expansion into adults and inflammatory bowel disease, becomes optionality on top.

The RMAT designation is doing more work than most investors realise

Rexlemestrocel-L carries FDA Regenerative Medicine Advanced Therapy designation for this indication. In plain English, that means the FDA has already agreed the mechanism and the disease qualify for the fastest regulatory pathway available to a cell therapy. Priority review and rolling submission are both on the table once the BLA is filed.

The FDA has also already signed off on the trial design and the 12-month primary endpoint. This matters because it removes one of the biggest historical risks with Mesoblast, which has been the regulator asking for more data after the fact. That happened in 2020 and again in 2023 with earlier Ryoncil filings.

Our take is that the regulatory setup here is materially cleaner than anything the company has attempted before. The risk sits almost entirely in the efficacy data itself, not in the pathway around it.

The 2027 readout is the moment the whole story pivots

Top-line results are expected in mid-CY2027 after the last treated patient completes 12 months of follow-up. That gives investors roughly a year of holding through anticipation, with commercial manufacturing scaling in the background. Management has clearly telegraphed intent to file the BLA as soon as possible after the readout.

The skeptical read is that Mesoblast has previously reported strong Phase 3 pain reduction data in MSB-DR003 and still needed a confirmatory trial. Investors who watched the graft versus host disease saga will remember how many times positive-looking data still required more work. A single well-powered study can still miss its primary endpoint.

The Investors Takeaway for Mesoblast

Ryoncil gives Mesoblast a real revenue base and improving balance sheet quality, but the back pain program is what determines whether this becomes a genuine multi-billion dollar biotech or stays a mid-cap specialty player. Enrolment completion removes one of the two remaining gating risks. Efficacy is the other, and that answer arrives in about 12 months.

We think the interesting question for investors right now is positioning ahead of that readout. The company has spent years earning back credibility with the FDA, and rexlemestrocel-L is the asset that would validate the whole platform thesis. Readers can see our earlier coverage of the Ryoncil commercial ramp and balance sheet reset at stocksdownunder.

The pattern we would watch through late CY2026 is manufacturing scale-up commentary, any additional detail on opioid cessation data from the earlier trial, and whether management starts guiding toward specific launch geographies. Those are the tells that internal confidence is building.