The US Food and Drug Administration (FDA) has granted an orphan drug designation to Priothera’s mocravimod for leukaemia patients undergoing a stem cell transplant.

The drug is indicated to help improve the outcome of patients with haematologic malignancies following a haematopoietic stem cell transplantation, according to a 27 November press release.

Following the designation, the Dublin, Ireland-headquartered biotech will now be in line for tax credits for US-based clinical trials and, if the therapy is approved, have seven years of market exclusivity in the designated indication.

Haematopoietic stem cell transplantation, also known as blood and bone marrow transplantation, is used to treat a wide range of blood cancers. There are nearly 60,000 new cases of leukaemia in the US each year.

This is the second orphan drug designation for Priothera’s mocravimod. The first, granted in March 2022, was for the treatment of acute myeloid leukaemia (AML) in patients undergoing hematopoietic stem cell transplantation. The first designation was aimed at preventing the graft-versus-host disease response – a disorder that occurs when the graft’s immune cells attack the patient’s tissue cells.

The orphan drug designation granted this week aims to improve the outcomes of patients by enhancing the graft-versus-leukaemia response – the effect of the donor marrow cells correctly identifying cancer cells as foreign and initiating an immune response.

Priothera’s candidate aims to prevent graft-versus-host disease whilst maintaining graft-versus-leukaemia response, according to the company’s website.

Mocravimod is a sphingosine-1-phosphate (S1P) receptor modulator. According to Priothera, targeting this pathway is known to reduce the proliferation of T cells from lymphatic tissues.

Priothera co-founder and CEO Florent Gros said: “The two orphan drug designations highlight mocravimod’s dual mode of action [which improves] allo-haematopoietic stem cell transplantation treatment outcomes in haematological malignancies to potentially increase the leukaemia free survival – graft-versus-leukaemia response – while reducing tissue damage resulting from the graft-versus-host disease.”

Mocravimod is currently being investigated in a Phase III trial (NCT05429632), called MO-TRANS, which aims to enrol around 250 patients with AML undergoing haematopoietic cell transplantation. Priothera will assess the efficacy and safety of the drug as an adjunctive and maintenance treatment.

In February 2023, Japan’s Pharmaceuticals and Medical Devices Agency (PMDA) granted clearance for the Phase III trial’s initiation in the country.

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