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# Mesoblast Sent Another Complete Response Letter
- URL: https://www.fdaweb.com/mesoblast-sent-another-complete-response-letter/
- Published: 2023-08-04T12:00:00.000Z
- Updated: 2026-09-14T18:48:34.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5155026

FDA has issued Mesoblast a second complete response letter on its BLA for remestemcel-L for treating pediatric steroid-refractory acute graft versus host disease (SR-aGVHD), requesting more data to support marketing approval. “To obtain the data required, Mesoblast will conduct a targeted, controlled study in the highest-risk adults with the greatest mortality,” the company says. “This adult study is in line with our overall commercial strategy, which envisioned a sequenced progression from pediatric to adult SR-aGVHD indications.” It notes that adults make up about 80% of the SR-aGVHD market.

Mesoblast says it plans to enroll adult patients at “highest mortality risk with SR-aGVHD where existing therapy has not improved outcomes and 90-day survival remains as low as 20-30%.” It will seek FDA agreement on the new trial’s design at a Type A meeting within 45 days.

In 2020, FDA issued a complete response letter on the original BLA and recommended that the company conduct at least one additional randomized, controlled study in adults or children to provide further evidence of the therapy’s effectiveness. Additionally, FDA identified a need for further scientific rationale to “demonstrate the relationship of potency measurements to the product’s biologic activity,” the company said at the time. “Assays measuring the potency of remestemcel-L will continue to be refined to provide further scientific rationale for its use in severe inflammatory diseases with high mortality risk,” it said.

Prior to the latest complete response action, FDA’s Oncologic Drugs Advisory Committee voted nine to one in favor of approving the therapy. The positive vote negated FDA briefing documents that challenged the biologic’s effectiveness and durability of patient responses ([see earlier story](https://www.fdaweb.com/fda-challenges-remestemcell-l-data/)).

Mesoblast earlier said the resubmission contains the following new information:

- new long-term survival data through at least four years for children enrolled in a Phase 3 trial,
- new outcome data following remestemcel-L use in high-risk disease activity and on survival using propensity-matching of children in the Phase 3 trial and controls stratified by validated biomarkers,
- new analyses of prospectively obtained data related to the validated potency assay,
- new analyses of clinical data obtained prospectively on manufacturing changes made during product development,
- new data on the validated potency assay, and
- a new specification for release of commercial product