Mesoblast completes enrolment in Phase 3 chronic back pain trial

Mesoblast has completed patient recruitment for its pivotal Phase 3 trial of rexlemestrocel-L in chronic low back pain (CLBP) associated with degenerative disc disease, the dual-listed Australian biotech announced on 29 April. The MSB-DR004 study has randomised at least 300 patients to a single intra-discal injection of the allogeneic stromal cell therapy or a sham procedure, with 12 months of follow-up required before topline data can be reported.

Topline results are expected in mid-2027, and a positive readout would support a Biologics Licence Application (BLA) to the US Food and Drug Administration, which Mesoblast is targeting for the third quarter of that year. The FDA has already agreed on the study design and the 12-month pain-reduction primary endpoint as an approvable basis for registration — an alignment that meaningfully de-risks the regulatory path. Rexlemestrocel-L also holds Regenerative Medicine Advanced Therapy (RMAT) designation for the indication, granting eligibility for rolling review and priority review once the BLA is filed.

Building on prior Phase 3 data

MSB-DR004 is a confirmatory trial designed to replicate findings from the earlier MSB-DR003 study, in which a single injection of rexlemestrocel-L produced clinically meaningful reductions in pain and opioid use sustained for up to three years. Secondary endpoints in MSB-DR004 include improvements in function and quality of life, as well as cessation of opioid medication — a secondary outcome with considerable public-health relevance given that discogenic back pain accounts for an estimated 50% of prescription opioid use in the United States.

Chief executive Silviu Itescu described the recruitment milestone as a major step toward "bringing to market a non-opioid, disease-modifying therapy for patients suffering from chronic low back pain, a condition with significant unmet medical need." Mesoblast estimates the US addressable population at over seven million people and has cited analyst projections pointing to peak revenues exceeding US$10 billion at single-digit market penetration — figures that should be treated as speculative at this stage of development.

Market and competitive context

The CLBP space has long attracted interest from device makers, pharmaceutical companies, and biologics developers, yet no disease-modifying treatment has reached the US market. Approved options remain limited to analgesics, physiotherapy, and interventional procedures including spinal fusion, all of which address symptoms rather than the underlying inflammatory and degenerative pathology. If rexlemestrocel-L succeeds, it would be the first cell therapy approved for a musculoskeletal pain indication and would build on Mesoblast's existing regulatory precedent: Ryoncil (remestemcel-L), the company's mesenchymal stromal cell therapy for steroid-refractory acute graft-versus-host disease in paediatric patients, became the first FDA-approved MSC therapy in 2024.

Competitors pursuing biological or regenerative approaches to disc disease include a number of early-stage university spinouts and venture-backed companies working on platelet-rich plasma, growth factor injection, and gene-therapy strategies, though none has advanced to late-stage confirmatory trials with an FDA-agreed design. That competitive gap, combined with the RMAT designation and a two-year head start on Phase 3 data generation, represents a meaningful near-term advantage for Mesoblast — though execution risk remains, and the company will need to demonstrate clean safety data alongside efficacy in the confirmatory readout.

Investors will focus on two near-term signals: interim safety reviews from the independent data monitoring committee, and any indication from Mesoblast about partnership or licensing discussions ahead of a potential commercial launch. The company already holds commercial partnerships in Japan, Europe, and China for its broader cell therapy portfolio, and a late-stage CLBP asset with an FDA-agreed BLA pathway would be a logical target for a large-pharma pain or musculoskeletal partnership.