Mesoblast has completed treatment of all 350 patients in its pivotal phase 3 trial of rexlemestrocel-L for chronic low back pain caused by inflammatory degenerative disc disease, putting the company on track for top-line results in mid-2027.
The trial, known as MSB-DR004, is testing whether a single intra-discal injection of the allogeneic stromal cell therapy can deliver durable pain relief at 12 months compared with a sham injection. The company initially planned to treat 300 patients but expanded enrolment to 350 following what it described as strong demand from investigators to include eligible patients in the study.
Mesoblast said the larger cohort leaves the study well powered to demonstrate a treatment benefit for rexlemestrocel-L. Beyond the primary pain endpoint, the trial will assess changes in physical function, quality of life and the use of pain medicines, including opioids.
Chief executive Silviu Itescu described completion of patient treatment as a momentous milestone for the company, with the focus now turning to the 12-month follow-up period and the eventual data readout.
If positive, the results could support a Biologics License Application in the United States for a therapy targeting a large, difficult-to-treat patient population with limited disease-modifying treatment options.
Rexlemestrocel-L has already received Regenerative Medicine Advanced Therapy designation from the US Food and Drug Administration for chronic low back pain associated with degenerative disc disease. The designation may make the product eligible for priority review once a biologics licence application is submitted, although regulatory approval will depend on the clinical data and the broader evidence package.
Mesoblast is positioning the therapy for patients with chronic low back pain linked to inflammatory degenerative disc disease of less than five years’ duration. The company says it has previously reached agreement with the FDA on the pivotal trial design and on the 12-month pain reduction endpoint as an approvable basis for the proposed indication.
The current phase 3 trial follows Mesoblast’s earlier MSB-DR003 study, in which the company reported meeting the same primary endpoint. The confirmatory study aims to determine whether that pain-reduction effect can be replicated in a larger randomised, placebo-controlled setting.
Chronic low back pain remains a substantial clinical and economic burden, particularly where degenerative disc disease and inflammation are involved. Mesoblast estimates that more than seven million people in the United States are affected by this form of back pain, which is associated with impaired mobility, reduced capacity to work, poorer quality of life and significant reliance on pain medicines.
The company also points to the potential relevance of the program in the context of opioid use, arguing that discogenic back pain represents a meaningful share of prescription opioid utilisation in the United States. Reduction in opioid use is therefore included as a secondary endpoint in the MSB-DR004 study.
The low back pain program sits alongside Mesoblast’s broader allogeneic cell therapy pipeline. Its lead commercial product, Ryoncil, is approved in the United States for steroid-refractory acute graft-versus-host disease in paediatric patients aged two months and older. The company is also developing remestemcel-L and rexlemestrocel-L across other inflammatory indications, including heart failure, adult graft-versus-host disease and inflammatory bowel disease.
