X4 Pharmaceuticals announced Monday morning that the FDA approved its daily pill for WHIM syndrome — an ultra-rare immune disease named after its symptoms.
The pill, mavorixafor, was approved for patients aged 12 and older with WHIM syndrome. X4 Pharmaceuticals will market the drug as Xolremdi.
The company priced the medicine at $496,400 per year for patients more than 50 kg (roughly 110 pounds) and $372,300 for those 50 kg or less, according to an SEC filing.
WHIM stands for warts, hypogammaglobulinemia, infections and myelokathexis. Hypogammaglobulinemia refers to low antibody levels, while myelokathexis is chronic low white blood cell count. There have been just over 100 cases published on the genetic immune disease worldwide, according to a 2019 editorial in the Journal of Allergy and Clinical Immunology, but like other ultra-rare diseases, WHIM syndrome is likely underdiagnosed and its true prevalence is unknown.
X4 Pharmaceuticals CEO Paula Ragan said the company estimates that there are about 1,000 patients who may be eligible for treatment in the US. “The limited number of patients is always based on limited information,” Ragan said. “Until there is a treatment available, no one ever knows how many patients are out there, because physicians have no motivation to diagnose.
“That’s a catch-22 that we can get into in these ultra-rare patient populations,” she said in an interview ahead of the approval.
“We think a continued expansion of education and awareness will increase physicians’ curiosity. Ultimately, we want them to get curious about, ‘What if it’s WHIM?’ and to think about diagnosis,” Ragan said, adding that the company offers free genetic testing.
Xolremdi addresses the cause of the disease — mutations to the CXCR4 gene that increase activity of the receptor the gene encodes. That increased activity stops white blood cells from leaving the bone marrow for the bloodstream, reducing the ability of a person with WHIM syndrome to fight pathogens. X4’s pill is a CXCR4 inhibitor, an old Sanofi drug candidate the company licensed at its founding in 2014. Ragan is an alumnus of the famed rare disease biotech Genzyme, which Sanofi acquired in 2011.
In a Phase 3 study, Xolremdi reduced infection frequency, severity and duration compared to placebo. It also increased the time that neutrophil counts were above a certain marker. Neutrophils are the most common type of white blood cell.
In a March note to investors, Stifel analysts projected that the drug will generate $6 million in sales this year, hitting $86 million in 2026.
X4 received a priority review voucher, which can be used to speed up review time for future therapies, from the approval of the drug. Ragan said the company plans to sell the voucher. They typically net companies about $100 million, which could help X4 to continue operating for approximately another year. X4 currently has enough cash to operate into 2025, it reported in March.
The company is also testing Xolremdi in chronic neutropenia — a condition where people have a low number of neutrophils for more than a few months — where it expects to begin a Phase 3 study this year.
Editor’s note: This story was updated with Xolremdi’s list price.