Mesoblast Reaches Key Milestone in Phase 3 Trial of Rexlemestrocel-L for Chronic Back Pain

Mesoblast Limited (ASX: MSB; Nasdaq: MESO), a global biotechnology company specializing in allogeneic cellular medicines for inflammatory diseases, has announced that it has reached its enrollment target of treating at least 300 patients in its pivotal Phase 3 clinical trial evaluating rexlemestrocel-L for chronic low back pain (CLBP) caused by degenerative disc disease (DDD). Achieving this milestone marks an important step toward completing the late-stage study and advancing the therapy toward potential regulatory approval.

The Phase 3 trial, known as MSB-DR004, is a randomized, placebo-controlled study designed to confirm the long-lasting pain relief observed in the company's earlier Phase 3 trial, MSB-DR003. Researchers are evaluating whether a single intra-discal injection of rexlemestrocel-L can provide sustained reductions in chronic back pain compared with placebo treatment.

Mesoblast Chief Executive Officer Silviu Itescu said reaching the target of treating at least 300 patients ensures that the study has sufficient statistical power to evaluate the therapy's effectiveness. He added that the company is simultaneously expanding its commercial manufacturing capabilities so it can move quickly toward regulatory submission once the clinical trial results become available.

Chronic low back pain associated with degenerative disc disease remains a significant health challenge, affecting more than seven million people in the United States alone. The condition is driven by inflammation and degeneration of the spinal discs, often leading to persistent pain, reduced mobility, and dependence on pain medications. Mesoblast believes the large patient population and limited treatment options make this a major commercial opportunity, with the therapy having the potential to generate peak annual revenues exceeding US$10 billion even with single-digit market penetration.

The primary objective of the Phase 3 trial is to demonstrate a statistically significant reduction in low back pain after 12 months in patients treated with rexlemestrocel-L compared with those receiving sham treatment. In addition to measuring pain relief, the study is also assessing several important secondary endpoints, including improvements in physical function, overall quality of life, and reductions or complete discontinuation of pain medications, including opioid use.

Rexlemestrocel-L has already received Regenerative Medicine Advanced Therapy (RMAT) designation from the U.S. Food and Drug Administration (FDA) for the treatment of chronic low back pain caused by degenerative disc disease. This designation provides several regulatory advantages, including eligibility for priority review and rolling submission of a Biologics License Application (BLA), which could help accelerate the review process once the company files for approval. Mesoblast expects to report top-line results from the Phase 3 study in mid-2027 after all enrolled patients have completed their 12-month follow-up period.

Rexlemestrocel-L is Mesoblast's second-generation, allogeneic stromal cell therapy manufactured using its proprietary STRO3 immunoselection technology. In the current study, the cell therapy is administered together with hyaluronic acid, which serves as a delivery agent for injection directly into the affected lumbar disc. The trial is enrolling patients across multiple clinical sites in the United States who have experienced chronic low back pain resulting from inflammatory degenerative disc disease for less than five years.

The design of the confirmatory Phase 3 study was previously agreed upon with the FDA, including the use of pain reduction at 12 months as the primary endpoint required to support potential approval. This endpoint was successfully achieved in Mesoblast's earlier Phase 3 study, providing encouraging evidence for the therapy's clinical benefit. The current trial is intended to confirm those findings in a larger patient population while also evaluating improvements in function and quality of life.

A key focus of the study is reducing patients' dependence on opioid medications. Disc-related chronic low back pain is estimated to account for nearly half of all prescription opioid use in the United States. In its previous Phase 3 trial, Mesoblast observed not only significant pain reduction but also meaningful rates of opioid discontinuation among treated patients, highlighting the therapy's potential to address both chronic pain and opioid reliance.

With patient enrollment and treatment now reaching its planned target, Mesoblast is progressing toward one of the final stages of clinical development for rexlemestrocel-L. If the upcoming Phase 3 results confirm the positive outcomes seen in earlier studies, the company plans to submit a Biologics License Application to the FDA, bringing the therapy a step closer to becoming a new treatment option for patients living with chronic low back pain caused by degenerative disc disease.