Xencor’s lead lupus antibody misses phase 2 endpoint

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The news caused Xencor’s stock to dip in premarket trading, before nearly recovering over the day. (Pixabay)

Topline results from a phase 2 study showed Xencor’s lead CD19-targeting antibody missed its primary endpoint in lupus, but the company described the data as a “positive trend” that still contained a “promising treatment effect” worthy of future study.

Xencor plans to move forward with a phase 3 study of XmAb5871 in a separate indication for IgG4-related disease, a chronic inflammatory disorder—while potentially seeking a partner to carry the drug the rest of the way forward in systemic lupus erythematosus, or SLE, according to President and CEO Bassil Dahiyat.

The news caused Xencor’s stock to dip in premarket trading, before nearly recovering over the day.

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The placebo-controlled study of XmAb5871 enrolled 104 participants with non-organ-threatening SLE, and measured the proportion of patients with no loss of improvement following a short regimen of intramuscular steroids to quiet the disease’s activity.

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After about seven-and-a-half months of XmAb5871 treatment every two weeks, 42% of patients maintained disease improvements, compared to 28.6% of those receiving placebo—missing statistical significance with a p-value of 0.18.

Xencor said the higher placebo response rate was caused by 10 patients from that arm withdrawing from the study, compared to the two that dropped out of the treatment arm.

The trial cleared its secondary endpoint, with treated patients taking a median of 76% longer to show losses in improvement. In addition, XmAb5871 had a safety profile in line with previous studies.

"Xencor completed this study to efficiently assess the potential of XmAb5871 in SLE, now the third indication where a promising treatment effect has been seen, after rheumatoid arthritis and IgG4-Related Disease," Dahiyat said in a statement. “With six internal programs in autoimmune disease and cancer advancing in the clinic, we anticipate additional data readouts over the next two years."