Xencor, a clinical-stage biopharmaceutical company developing engineered monoclonal antibodies, announced that XmAb 5871 has been granted orphan drug designation by the US Food and Drug Administration (FDA) for the treatment of IgG4-Related Disease (IgG4-RD), a newly defined fibro-inflammatory autoimmune disorder that is estimated to impact up to 40,000 patients in the United States.

"There currently are no approved therapies for IgG4-RD, an immune-mediated condition responsible for fibro-inflammatory lesions that can lead to irreversible damage to virtually any organ," said Bassil Dahiyat, Ph.D., president and chief executive officer of Xencor. "New treatment options are clearly needed, and we are diligently moving XmAb5871 forward in clinical development to fill this void. Preliminary data from our Phase 2 study of XmAb5871 showed promising activity in patients with IgG4-RD, and we are on track to complete the study and report topline results by the end of this year.  We are also planning to engage the FDA later this year to discuss future clinical trials and potential registration requirements in IgG4-RD."

The FDA's Orphan Drug Designation program provides orphan status to drugs defined as those intended for the safe and effective treatment, diagnosis or prevention of rare diseases that affect fewer than 200,000 people in the US Orphan designation qualifies the sponsor of the drug for certain development incentives, including tax credits for qualified clinical testing, prescription drug user fee exemptions and seven-year marketing exclusivity upon FDA approval.

XmAb5871 is a first-in-class monoclonal antibody that targets CD19 with its variable domain and that uses Xencor's XmAb immune inhibitor Fc domain to target Fc?RIIb, a receptor that inhibits B-cell function. XmAb5871 is the first drug candidate that Xencor is aware of that targets Fc?RIIb inhibition. Xencor has demonstrated in multiple animal models and in initial human clinical trials that XmAb5871 inhibits B-cell function without destroying these important immune cells. Preliminary phase 2 data presented at the American College of Rheumatology 2016 Annual Meeting showed that 82 per cent of patients who received XmAb5871 achieved an initial response to therapy within 2 weeks of their first dose with responses deepening over time.