Xencor (XNCR) Announces Prelim. XmAb5871 Phase 2 Data; 82% Initial Response Reported

November 13, 2016 9:11 AM EST

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Xencor, Inc. (Nasdaq: XNCR) announced preliminary data from XmAb5871-03, an ongoing, open-label, pilot Phase 2 study of XmAb5871 in patients with active IgG4- RD. Data show that 82% of patients achieved an initial response to therapy within two weeks of their first dose. The data are being presented by John H. Stone, M.D., MPH, director of rheumatology at Massachusetts General Hospital, at the American College of Rheumatology (ACR) 2016 Annual Meeting in the Miscellaneous Rheumatic and Inflammatory Disease session on Sunday, November 13, 2016 (today) at 2:45 p.m. EST.

"We are very encouraged by the rapid initial response in IgG4-RD disease activity observed in this preliminary data set, in which nine of the 11 patients evaluated for IgG4-RD Responder Index (RI) post-treatment achieved a response within two weeks of their first dose, with responses typically deepening over time," said Paul Foster, M.D., chief medical officer of Xencor. "We expect to report complete study results in 2017."

"I am impressed by the steady 'dialing down' of the inflammatory response that XmAb5871 seems to exert in IgG4-RD and believe it is a promising potential therapy," said Dr. John H. Stone, the principal investigator of the study. "We are learning a lot about how to study this disease in the context of this small trial."

As of a data cutoff of October 31, 2016, 12 patients with active IgG4-RD have been enrolled and dosed with XmAb5871 (median number of infusions = 7, range 1-12). Patients had a median IgG4-RD RI of 10 (range 2-30) with a median of four organs involved (range 1-10) at the time of study entry. Organ site involvement occurring at a frequency of greater than or equal to 50% included lymph nodes, submandibular glands, parotid glands and lacrimal glands.

Preliminary Safety Data:

Every other week intravenous administration of XmAb5871 has been well tolerated. As of October 31, 2016, no serious adverse events (AEs) have been reported. Treatment related AEs have occurred in five patients (42%). Treatment-related AEs that occurred in more than one patient were abdominal pain/discomfort in three patients (25%), occurring as part of Grade 1 (mild) infusion-related gastrointestinal symptoms (nausea and/or vomiting and/or diarrhea) during the first infusion, and Grade 1 (mild) headache in two patients (16.7%). One patient discontinued the study as the result of an AE. The patient developed a Grade 2 (moderate) hypersensitivity reaction with rash and arthritis, commonly referred to as serum sickness, following the fifth infusion. The event resolved quickly without the need for medical management. This patient was subsequently found to have developed anti-drug antibodies.

Preliminary Efficacy Data:

Eleven of the 12 patients dosed with XmAb5871 have had at least one IgG4-RD RI performed following dosing as of the data cutoff date. Nine of 11 patients (82%) have had an initial response to XmAb5871 therapy of at least a three-point reduction in the IgG4-RD RI within two weeks of the first dose. Five patients attained disease remission (an IgG4-RD RI of 0) during the study. Two patients entering the study on corticosteroids have been able to taper and discontinue steroid use during the study.

In addition to the patient with early study termination due to an AE, two other patients have discontinued treatment prior to receipt of all 12 planned infusions. One patient had a response to therapy (IgG4-RD RI reduction of six points), but lost response following the sixth infusion, at which point this patient discontinued treatment. One patient had no response to therapy as defined by a greater than or equal to two-point decrease in the IgG4-RD RI. This patient had an atypical presentation of larynx involvement as the only organ involved. The patient discontinued the study after six infusions. Neither of these two patients have responded to subsequent rituximab treatment.

The slide presentation will be available at 3:00 p.m. Eastern Time today on the 'Investors' page of Xencor's website under 'Events and Presentations' at www.xencor.com.

Conference Call InformationXencor management will host a conference call and webcast today at 6:00 p.m. Eastern Time to discuss data presented today. The live call may be accessed by dialing (877) 359-9508 for domestic callers or (224) 357-2393 for international callers, and providing the conference ID number 16658995. A live webcast of the conference call will be available online from the investors section of the Xencor website at www.xencor.com. The webcast will be archived on the Company's website for 30 days.

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