Key Highlights

  • Mesoblast (ASX: MSB) shares were at A$2.41, up 9.05% or A$0.20 at 2:58pm on 17 August 2026.
  • The company completed treatment of 350 patients in its pivotal randomized Phase 3 MSB-DR004 trial for chronic low back pain.
  • The trial's primary endpoint is designed to assess durable pain reduction at 12 months following a single intradiscal injection of rexlemestrocel-L.
  • Top-line results are expected in mid-2027, while rexlemestrocel-L has FDA Regenerative Medicine Advanced Therapy designation for the indication.

Mesoblast Limited (ASX:MSB) was trading at A$2.41, up 9.05%, or A$0.20, at 2:58pm on 17 August 2026. The share-price movement came on the same day the company announced completion of patient treatment in its pivotal Phase 3 trial of rexlemestrocel-L for chronic low back pain associated with degenerative disc disease. Mesoblast said 350 patients had been randomized and treated, above the previously targeted 300-patient enrolment level.

Phase 3 Trial Reaches Treatment Milestone

The MSB-DR004 trial is evaluating rexlemestrocel-L in patients with chronic low back pain associated with inflammatory degenerative disc disease. Participants received either an intradiscal injection of the cell therapy candidate or a sham injection.

Mesoblast initially targeted treatment of at least 300 patients, a milestone it reported reaching in July. The subsequent increase to 350 treated patients followed Demand from investigators seeking to enrol additional patients. The larger treated population is intended to provide the trial with greater statistical power to assess the treatment effect compared with the control group.

The primary endpoint is focused on pain reduction at 12 months. Secondary measures include changes in physical function and quality of life, as well as cessation or reduction of pain medication, including opioids.

Results Timeline Moves Into Focus

With treatment completed, the next major clinical milestone is the 12-month follow-up assessment. Mesoblast expects top-line results in mid-calendar 2027, after the last treated patient has completed the required follow-up period. Earlier company materials had similarly placed the top-line readout around mid-2027.

The timing is significant for the development program because the company is seeking to confirm the pain-reduction outcome observed in its earlier MSB-DR003 Phase 3 trial. Mesoblast has said the FDA has agreed to the trial design and the 12-month pain-reduction endpoint as the approvable indication.

The current study therefore remains a clinical-development program, with the eventual regulatory pathway dependent on the results and subsequent regulatory review.

FDA Designation and Commercial Context

Rexlemestrocel-L has received Regenerative Medicine Advanced Therapy (RMAT) designation from the U.S. Food and Drug Administration for chronic low back pain associated with degenerative disc disease. The designation provides certain regulatory benefits, including eligibility for priority review when a Biologics License Application is filed.

Mesoblast has described the U.S. chronic low back pain population associated with inflammatory degenerative disc disease as exceeding seven million people. The company has also previously stated that the indication could represent a significant commercial opportunity if the therapy is successfully developed and approved.

The company is not relying solely on rexlemestrocel-L. Mesoblast's Ryoncil product, remestemcel-L-rknd, is already FDA-approved for steroid-refractory acute graft-versus-host disease in pediatric patients aged two months and older. Earlier company reporting showed Ryoncil gross sales of US$35 million and net Revenue of US$30 million for the December 2025 quarter.

Development Risk Remains

Despite the treatment milestone, the Phase 3 program still has a substantial clinical step ahead. The current trial has yet to deliver its primary endpoint results, and completion of patient treatment does not establish efficacy or regulatory approval.

Mesoblast's earlier development history also demonstrates the importance of regulatory and Manufacturing requirements in cell therapy programs. In 2023, the U.S. FDA issued a complete response to an earlier BLA for remestemcel-L in pediatric steroid-refractory acute graft-versus-host disease and requested additional data.

Conclusion

Mesoblast's completion of treatment for 350 patients marks an important operational milestone for its pivotal Phase 3 chronic low back pain program. The increase from the original 300-patient target provides a larger treated population for the 12-month assessment, while the company's FDA RMAT designation provides a defined regulatory framework for rexlemestrocel-L. The next major event is the expected mid-2027 top-line readout, meaning the company's clinical and corporate narrative is now increasingly centred on the outcome of the MSB-DR004 trial.