FDA Grants Rare Pediatric Disease Designation to X4 Pharma’s Treatment for WHIM Syndrome

Rare Daily Staff

The U.S. Food and Drug Administration granted Rare Pediatric Disease designation to X4 Pharmaceuticals’ mavorixafor, for the treatment of WHIM syndrome in patients who are 12 years of age and older.

Mavorixafor is currently being investigated in a global pivotal phase 3 clinical trial, 4WHIM, for the treatment of WHIM syndrome in patients who are 12 years of age and older.

WHIM syndrome is a rare, primary immunodeficiency disease caused by genetic mutations in the CXCR4 receptor gene. It is named for the characteristic clinical symptoms of the syndrome—warts, hypogammaglobulinemia, infections, and myelokathexis. Patients with WHIM may experience significant morbidity beginning in early childhood and continuing throughout life with an increased likelihood of various recurrent, potentially life-threatening infections, and may also be susceptible to malignancies such as HPV-related cervical cancer and lymphomas. The overall cancer risk in patients with WHIM is estimated to be 30 percent by 40 years of age. There are no approved therapies for WHIM. X4 Pharma estimates there to be more than 3,500 diagnosed and undiagnosed WHIM patients in the U.S.

Mavorixafor is a potential first-in-class, once-daily, oral, small molecule antagonist of chemokine receptor CXCR4, and is currently being investigated in a pivotal phase 3 global clinical trial for the treatment of WHIM syndrome. Results are expected in 2022.

“WHIM is a congenital disease that affects individuals of all ages. Children, in particular, have been shown to experience serious or life-threatening bacterial infections that can require hospitalizations. There are currently no treatments available that address the underlying genetic cause of WHIM,” said Paula Ragan, president and CEO of X4 Pharmaceuticals. “The RPD designation reinforces the clear unmet need for a disease modifying therapy in both pediatric and adult patient populations.”

Mavorixafor has previously been granted Fast Track, and Breakthrough Therapy designations by the FDA, as well as Orphan Drug status by the FDA and the European Commission, for the treatment of WHIM syndrome in adults.

The FDA grants Rare Pediatric Disease designation for serious or life-threatening diseases with manifestations in individuals aged from birth to 18 years, including access to the FDA’s expedited review and approval process. The designation makes mavorixafor eligible for a Rare Pediatric Disease Priority Review voucher upon approval of the therapy by the FDA.

The vouchers can be used to reduce the time of an FDA new drug approval review to six months from ten months. The vouchers are potentially lucrative because they are transferable. Most recently, Eiger BioPharmaceuticals sold its priority review voucher for $95 million in November 2020.

The voucher program was due to expire at the end of September but Congress provided a short-term extension of the program. According to the current statutory sunset provisions, after December 11, 2020, FDA may only award a voucher for an approved rare pediatric disease product application if the sponsor has rare pediatric disease designation for the drug, and that designation was granted by December 11, 2020. After December 11, 2022, FDA may not award any rare pediatric disease priority review vouchers.

Going forward, submitted requests for rare pediatric disease designation will be reviewed in a timely manner but the FDA’s previous 60-day response time no longer applies.

Photo: Paula Ragan, president and CEO of X4 Pharmaceuticals