Highlights:

• Dosing is finished in Mesoblast's pivotal MSB-DR004 study of rexlemestrocel-L for chronic low back pain.
• A total of 350 people were randomised and treated, more than the minimum of 300 the company had set.
• The 12-month primary endpoint reads out in mid-CY2027, setting up the next hard catalyst for the stock.

The Last Patient Has Been DosedMesoblast Limited (ASX: MSB) has finished treating patients in MSB-DR004, the pivotal Phase 3 study testing its allogeneic stromal cell candidate rexlemestrocel-L in chronic low back pain caused by degenerative disc disease. The company disclosed the milestone on 16 August 2026 in New York, which reached the ASX on the morning of 17 August.

Every participant received a single injection into the lumbar disc — either rexlemestrocel-L or a sham procedure. Dosing ran past the company's stated minimum of 300 patients and closed at 350, an overshoot Mesoblast attributes to trial investigators pushing to get more of their patients into the study.The market took the news well. MSB shares were last quoted at AU$2.450, a gain of AU$0.240 or 10.86% on the previous close of AU$2.210.

Everything Now Rests on the 12-Month NumberThe study's primary endpoint is whether one injection produces pain relief that holds up a full year later. That is not a novel question for the company: the earlier MSB-DR003 study produced exactly that signal, and MSB-DR004 exists to confirm it in the patient subgroup most likely to respond. The FDA signed off on both the study design and the 12-month pain endpoint as an approvable basis for filing.

Beyond pain scores, investigators are tracking function, quality of life, and whether patients cut back or stop analgesics altogether. Opioids get particular attention, since Mesoblast cites data putting discogenic back pain behind roughly half of US prescription opioid use — which makes an opioid-sparing result commercially and politically valuable in its own right. Chief Executive Silviu Itescu framed the milestone as the start of a countdown to a read-out he hopes will underpin the company's first blockbuster.

Top-line data are guided for mid-CY2027, timed to the last treated patient clearing 12 months of follow-up. Rexlemestrocel-L already carries Regenerative Medicine Advanced Therapy designation from the FDA in this indication, which would make a Biologics License Application eligible for priority review once filed.Sizing the PrizeMesoblast puts the US population with chronic low back pain from degenerative disc disease at more than 7 million. On the company's own numbers, capturing only a single-digit slice of that market would still support peak annual revenue above US$10 billion. That figure is a company projection rather than an independent estimate, and it assumes both a successful trial and a pricing and reimbursement environment that has yet to be tested for a therapy of this type.What Investors Should WatchThe execution risk that dominated the past two years — slow recruitment, drifting timelines, cash burn against an unfinished trial — is now largely behind the company. What replaces it is cleaner and less forgiving: a single binary data point roughly ten months out. No efficacy or safety readings from MSB-DR004 have been released, and Mesoblast's history includes setbacks that hit the stock hard. Between now and mid-2027, there is little left to de-risk and nothing to do but wait for the number.

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