A clearer risk assessment

Exagen’s PC4d biomarker shows promise in determining lupus patients at risk of thrombosis

Kelsey Kaustinen
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SAN DIEGO & ALBUQUERQUE, N.M.—Earlier in the quarter, Exagen Inc. shared data regarding its patented PC4d biomarker that supports its potential in addressing thrombosis in lupus patients. The results were published in Lupus Science & Medicine, in an article titled “Platelet-bound C4d, low C3 and lupus anticoagulant associate with thrombosis in SLE.” The results seem to demonstrate that platelet-bound C4d (PC4d) can offer additional insight into a patient’s risk of thrombosis beyond that of standard biomarkers.
“Patients with lupus have a higher incidence of thrombosis compared to the general population; however, not all lupus patients will encounter a thrombotic event. The challenge is knowing which lupus patients are at an elevated risk and therefore candidates for interventional therapy,” Brian McEvilly, vice president of marketing at Exagen, tells DDNews. “Depending upon each patient’s situation, a provider may recommend simple dietary changes or daily baby aspirin, but if the risk is deemed severe, then anti-coagulant therapy may be appropriate. Current risk factors include antiphospholipid antibodies, soluble complement levels and lupus anticoagulant tests, but often these tests alone are insufficient to make a decision regarding lifelong therapy choices.”
Per the paper, “The excessive risk of thrombosis in SLE is dependent on the presence of abnormalities that are specific for the disease, including low C3, antiphospholipid (aPL) antibodies (in particular lupus anticoagulant [LAC]) and nephrotic syndrome. Other factors related to SLE treatment such as prednisone may further elevate the risk of thrombosis ... SLE is an immune complex disease linked to classical complement pathway activation, hyperconsumption of C3 and C4 proteins, and production of C4d split fragments covalently bound to a variety of haematopoietic cells, including the erythrocytes, the B lymphocytes and the platelets. The complement system, platelets and coagulation pathways interact. This is the first report of a composite risk index which includes measures of these pathways and which highlights the additive association with thrombosis in SLE.”
PC4d is one of Exagen’s cell-bound complement activation products, or CB-CAPs, a group of assays that includes EC4d, BC4d and PC4d, all of which are stable biomarkers of complement activation. As noted in a press release, “Measuring deposits resulting from activation of the complement system offers additional insight about the extent to which lupus and the complement system are active in the circulation of an individual patient.”
“Elevated PC4d is highly specific for lupus in general, although only about 20 percent of lupus patients will have elevated levels,” McEvilly explains. “It has been associated with specific forms of thrombosis, including ischemic stroke.”
“Certain factors, including the common lupus treatment prednisone, can elevate the risk of thrombosis,” he adds. “Patients with lupus have an increased risk for thrombosis. Arterial and/or venous thrombosis is a well-known clinical entity in SLE, with a prevalence >10 percent. This prevalence may even exceed 50 percent in high-risk patients.”
“We know that SLE patients with antiphospholipid antibodies—particularly the lupus anticoagulant—are at increased risk of thrombosis, but our ability to predict who is at highest risk is woefully inadequate,” said Dr. Michelle Petri, a professor of medicine at the Johns Hopkins University School of Medicine, director of the Hopkins Lupus Cohort and an author of the Lupus Science & Medicine paper. “The Hopkins Thrombosis Risk Score, developed in collaboration with Exagen, has included the multifactorial nature of the risk, particularly the involvement of two other pathways: low complement, and complement split products bound to platelets (an assay initially developed by Drs. Joe Ahearn and Sue Manzi). We recognize that this risk score requires prospective and external validation.”
According to Ron Rocca, CEO of Exagen, “We are the only company developing novel instruments like PC4d for the rheumatology community. We recognize that patients suffering from lupus and related conditions face immense challenges in trying to reduce or control their lupus. The findings that PC4d is associated with a history of thrombosis mean that every lupus patient and their doctors will now have access to information about one of the major complications associated with their condition.”
McEvilly tells DDNews that Exagen plans to pursue further studies in lupus, and notes that the company’s portfolio also offers options for the diagnosis of antiphospholipid syndrome, myositis, rheumatoid arthritis, Sjogren’s syndrome, scleroderma and autoimmune thyroiditis.

Kelsey Kaustinen

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