FDA Approves X4 Pharmaceuticals' Mavorixafor As First Therapy For Rare Immunodeficiency Disorder

The FDA approved on Monday X4 Pharmaceuticals Inc’s XFOR Xolremdi (mavorixafor) capsules for use in patients 12 years of age and older with WHIM syndrome (warts, hypogammaglobulinemia, infections and myelokathexis) to increase the number of circulating mature neutrophils and lymphocytes.

Xolremdi, a selective CXC chemokine receptor 4 (CXCR4) antagonist, is the first therapy specifically indicated in patients with WHIM syndrome, a rare, combined primary immunodeficiency and chronic neutropenic disorder caused by CXCR4 pathway dysfunction. 

People with WHIM syndrome characteristically have low blood levels of neutrophils (neutropenia) and lymphocytes (lymphopenia) and experience serious and/or frequent infections. 

The FDA approval of Xolremdi was based on 4WHIM Phase 3 trial results.

The efficacy of Xolremdi was determined by improvement in absolute neutrophil counts (ANC), absolute lymphocyte counts (ALC), and a reduction in infections. 

Xolremdi treatment demonstrated increased time above threshold (≥500 cells/microliter) for absolute neutrophil count (TAT-ANC) versus placebo and increased time above threshold (≥1000 cells/microliter) for absolute lymphocyte count (TAT-ALC) v. placebo. 

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The efficacy of Xolremdi was further assessed in a composite endpoint consisting of total infection score and total wart change score using a Win-Ratio method. 

Analyses of the individual components of this composite endpoint showed an approximate 40% reduction in total infection score, weighted by infection severity, in Xolremdi-treated patients compared with placebo-treated patients. 

There was no difference in total wart change scores between the Xolremdi and placebo treatment arms over the 52 weeks. 

Treatment with Xolremdi also resulted in a 60% reduction in the annualized infection rate compared with placebo-treated patients. 

With the FDA approval of Xolremdi, X4 has received a Rare Pediatric Disease Priority Review Voucher that can be used to obtain priority review for a subsequent application or sold to another drug sponsor.

Reuters noted the company set a wholesale acquisition cost for Xolremdi annually at $496,400 for patients greater than 50 kilograms (@110 lbs.) and $372,300 for patients less than or equal to 50 kilograms.

Citing Brookline Capital Markets analyst, Reuters noted the approval to treat WHIM could lead to 2024 sales of $54.6 million for the therapy. With a second indication in 2025, product sales could grow to $450.9 million in 2027.

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XFOR Price Action: XFOR shares are up 2.14% at $1.19 at publication Monday.

Photo: Julia Koblitz via Unsplash