In Search of Biomarkers for Granulomatosis with Polyangiitis (Wegener’s)

By Atul Khasnis, MD, MS

Cleveland Clinic’s Center for Vasculitis Care and Research each year manages more than 500 patients with granulomatosis with polyangiitis (GPA; Wegener’s). This patient volume confers a responsibility to study GPA while also positioning us well to do so. Our efforts in this area include a distinctive ongoing collaboration with Case Western Reserve University (CWRU), profiled below, to study immunologic perturbations in GPA prospectively.

Unmet Needs in Our Understanding of GPA

GPA is an uncommon but potentially life-threatening disease characterized by granulomatous inflammation and, typically, medium and small vessel vasculitis. Affected patients experience serious morbidity from effects of the disease itself and the immunosuppressive medications used to treat it. Patients and their physicians share a strong need to better understand this unusual and uncommon disease.

The immunologic underpinnings of GPA are incompletely understood. Anti-neutrophil cytoplasmic antibodies (ANCAs) are observed in GPA, but their role in pathogenesis is controversial. Gaining immunologic insights into GPA will enable better understanding of the mechanisms of disease onset and sustenance and the triggers of relapse. It also will help identify potential therapeutic targets. All of this will allow for better disease management and patient care.

Identification of reliable biomarkers of disease activity is a longstanding need in GPA. Comparing immunologic parameters during active disease and remission ‒ an important focus of our research collaboration ‒ may yield insights into such potential biomarkers.

The Research Project at a Glance

Our collaboration with CWRU is a prospective observational study funded through Cleveland Clinic’s R.J. Fasenmyer Center for Clinical Immunology. Patients in the study are managed by their own rheumatologists while the research team periodically collects clinical data (captured in an electronic database) paired with blood samples for immunologic studies on a longitudinal basis. The blood samples are sent to the clinical research unit laboratory at Cleveland Clinic, where they are processed for immunologic cells, serum and plasma. These samples are then frozen and stored until they undergo immunologic analyses by two experienced immunology labs at CWRU.

Our interest lies in examining the immune systems of patients with GPA in detail, so we are analyzing T cells, B cells (Figure 1), monocytes and dendritic cells for phenotype, activation, exhaustion and cycling by flow cytometry. In the future, based on preliminary data, we plan to perform functional studies on these cell subsets in the hope of advancing our understanding of their role in disease pathogenesis. We plan to extend these immunologic studies to neutrophils as well, as neutrophils likely play an important role in GPA pathogenesis. One unanswered question is whether immunologic disturbances observed in peripheral blood accurately reflect immunologic perturbations in inflamed tissues. While we are now performing these studies on peripheral blood, we hope to perform relevant studies on tissue samples obtained for clinically indicated reasons in the future.

Figure 1. B-cell gating strategy for assessment of B-cell subset frequencies in patients with granulomatosis with polyangiitis (GPA; Wegener’s).

Three Primary Research Goals

The project’s three main goals are:

• To study differences in patients’ immune systems during active GPA disease and remission. This will allow us to better understandmechanisms that drive systemic inflammation in GPA. Wealso plan to search for B-cell subsets that may be responsiblefor ANCA production. By comparing the immunologic profiles ofactive disease and remission in GPA, we hope to identify clinicallyuseful immunologic biomarkers of disease activity that canbe validated in a patient population of appropriate sample size.Determining disease activity has implications for changing immunosuppression,which is fraught with risk of medication toxicity.Thus the identification of biomarkers promises to facilitate therapeuticdecision-making.
• To elucidate the effects of rituximab on the immune systems of patients with GPA. Rituximab (RTX), an anti-CD20 monoclonalantibody (biologic agent), has been approved by the FDA fortreatment of GPA. Its main mechanism is thought to be eliminationof B-cell subsets that bear CD20 on their surface. Since Bcells are part of the immune system(a network), it is plausiblethat deleting B cells may have qualitative and quantitative impacton other immune cells. We are attempting to evaluate theeffects of RTX beyond B-cell depletion, such as effects on theimmunologic profiles of other immune cells during B-cell depletionand reconstitution. We are comparing patients who receiveRTX with those who have received nonbiologic immunosuppression,with the aim of understanding any unique immunologicaspects of RTX-mediated immunosuppression in GPA.
• To identify predictors of relapse in GPA. GPA is a relapsing disease, and the cause of relapse is unknown. Ongoing relapses can lead to accrual of organ damage, resulting in increased morbidity and significant impact on quality of life. Since we plan to enroll patients during remission and follow them longitudinally, we will have an opportunity to identify any consistent immunologic changes predating a flare (i.e., “immunologic signatures”) that could be used to guide therapeutic decisions once validated in an appropriately sized patient population.

Benefits in External Validity and Ongoing Collaboration

This project offers a unique opportunity to understand the pathogenesis of GPA. Because this is an observational study and none of its clinical management decisions are influenced by the research protocol, it provides a high level of external validity (i.e., real-world applicability). It also represents an ongoing collaboration between two major academic institutions, Cleveland Clinic and CWRU, that is likely to meaningfully advance our understanding of GPA.

The project’s other key investigators are Leonard Calabrese, DO, and Carol Langford, MD, MHS, of Cleveland Clinic, and Michael Lederman, MD, and Donald Anthony, MD, PhD, of CWRU.

Dr. Khasnis is a staff physician in the Center for Vasculitis Care and Research and the R.J. Fasenmyer Center for Clinical Immunology, both in the Department of Rheumatic and Immunologic Diseases.