The Food and Drug Administration (FDA) has issued a Complete Response Letter (CRL) to Omeros Corporation regarding the Biologics License Application (BLA) for narsoplimab in the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy (HSCT-TMA).

Narsoplimab is a human monoclonal antibody that specifically targets mannan-binding lectin-associated serine protease-2 and is designed to prevent complement-mediated inflammation and endothelial damage. The BLA submission included data from a single-arm, open-label phase 2 trial that enrolled 28 adult HSCT-TMA patients at high risk with a large majority having multiple comorbidities at baseline.

The FDA had originally set a Prescription Drug User Fee Act (PDUFA) date of July 17, 2021 to complete its review of the application; however, in May 2021, Omeros was asked to submit further information to the Agency that subsequently resulted in a review extension to October 17, 2021.

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In the CRL, the FDA noted that additional information would again be required to support approval, as the Agency could not estimate the treatment effect of narsoplimab in this patient population based on the available data submitted.

The Company is planning to request a meeting with the FDA to determine what will be needed to move the approval process forward. If approved, narsoplimab would be the first drug therapy indicated for HSCT-TMA.


  1. Omeros receives Complete Response Letter from FDA for Biologics License Application for narsoplimab in the treatment of HSCT-TMA. News release. October 18, 2021.
  2. Omeros announces extension of FDA review period for narsoplimab in HSCT-TMA. News release. May 20, 2021.

This article originally appeared on MPR