SNOWMASS, COLO. – Progress in the understanding and treatment of immunoglobulin G4–related disease is occurring “at lightning speed,” John H. Stone, MD, said at the Winter Rheumatology Symposium sponsored by the American College of Rheumatology.
Eight or nine years ago no one had heard of immunoglobulin G4–related disease (IgG4-RD). Today, because of the broad swath the disease cuts, it’s a hot research topic in every subspecialty of medicine as well as surgery, pathology, and radiology.
Bruce Jancin/Frontline Medical News
Dr. John H. Stone
This new understanding of IgG4-RD, he added, is opening the door to novel treatments.
“This is not a new disease. It was there when we were all in medical school, and for hundreds of years before that. But it’s really only in the last decade that we have come to understand that the disease can affect literally every organ system in the body with syndromes that we once thought were isolated organ-specific syndromes but we now recognize are part of a multiorgan disease currently called IgG4-related disease,” the rheumatologist said.
IgG4-RD is an immune-mediated fibroinflammatory condition characterized histopathologically by three hallmark features in involved tissue: obliterative phlebitis, storiform fibrosis, and a dense lymphoplasmacytic infiltrate.
Clinically, IgG4-RD often presents as a mass lesion that can affect any organ.
“I have many patients who’ve undergone modified Whipple procedures because they were thought to have adenocarcinoma of the pancreas,” according to Dr. Stone.
Other common presentations include Riedel’s thyroiditis, autoimmune pancreatitis, sclerosing cholangitis, sialadenitis, dacryoadenitis, periaortitis, an eosinophilic rash, and pseudotumor of the lung, lymph nodes, or orbits.
“Retroperitoneal fibrosis is a common and underappreciated manifestation. It may be the most common subsyndrome associated with IgG4-related disease,” he observed.
Another common presentation involves atopic disease – asthma, allergic rhinitis, eczema, eosinophilia, nasal polyps – developing out of the blue in middle age or later life. This observation led some other investigators to posit that IgG4-RD is a T-helper type 2–driven disease, an assertion debunked by Dr. Stone and coworkers (Allergy. 2014 Feb;69[2]:269-72).
Dr. Stone and his coinvestigators have published the largest series of patients with biopsy-proven IgG4-RD reported to date (Arthritis Rheumatol. 2015 Sep; 67[9]:2466-75). The average age at disease onset was 50 years. Of note, multiorgan involvement was the norm: 24% of patients had two organs involved, and 38% had three or more.
Analysis of this large patient series has led Dr. Stone to a surprising conclusion about the nature of IgG4-RD: “We have greatly overemphasized the importance of IgG4 in this condition,” he asserted.
Indeed, a mere 51% of the patients with clinically active untreated IgG4-RD in his series had an elevated serum IgG level. Dr. Stone characterized IgG4 as “kind of a wimpy antibody” incapable of driving the disease process because it is a noninflammatory immunoglobulin. This has led to speculation that IgG4 functions as what he termed an “antigen sink,” attempting to bind antigen at sites of inflammation.
But while an elevated serum IgG4 is of limited utility for diagnostic purposes, Dr. Stone and coworkers have demonstrated that it is of value as a predictor of relapse. Among patients with a treatment-induced remission, those in the top quartile in terms of baseline pretreatment serum IgG4 were 6.2-fold more likely to relapse (Rheumatology [Oxford]. 2016 Jun;55[6]:1000-8).
“This is a very useful marker for patients who are going to need chronic ongoing therapy. The notion of putting such patients on steroids for months and years is not appealing,” he said.
Levels of circulating plasmablasts as measured by peripheral blood flow cytometry, especially IgG4-positive plasmablasts, have proven much more helpful than serum IgG4 levels as a diagnostic tool, a reliable biomarker of disease activity, and a therapeutic target. Levels of these short-lived CD19+CD38+CD27+ plasmablasts are enormously elevated independent of serum IgG4 in patients with active IgG4-RD.
“One of the questions I’m most often asked is whether IgG4-related disease is a premalignant condition. My answer is no. The plasmablast expansion is oligoclonal, not polyclonal,” Dr. Stone continued.
He described IgG4-RD as “a continuous dance between T cells and B cells.” The latest thinking regarding pathogenesis is that type 2 T follicular helper cells activate B cells, which become memory B cells or plasmablasts. These activated B cells and plasmablasts present antigen to CD4+ cytotoxic T cells at sites of disease. Dr. Stone and his coinvestigators recently identified these CD4+ cytotoxic T cells as a novel population of clonally expanded T cells with SLAMF7 as a surface marker. The cells secrete interferon-gamma, interleukin-1, and transforming growth factor-beta, all of which are capable of driving the intense fibrosis characteristic of IgG4-RD. In addition, these CD4+ cytotoxic T cells secrete granzyme B and perforin, previously thought to be released mainly by natural killer T cells.
Joint American College of Rheumatology/European League Against Rheumatism classification criteria for the disease are expected to be finalized this winter at the Third International Symposium on IgG4-Related Diseases.
Treatment with rituxumab
Glucocorticoids remain the first-line therapy in IgG4-related disease, but it’s essential to bear in mind that their long-term efficacy in this immune-mediated fibroinflammatory disease is the exception rather than the rule, Dr. Stone said at the symposium.
Dr. Stone was a coauthor of an international expert consensus statement on the treatment of IgG4-related disease (IgG4-RD), which emphasized that point (Arthritis Rheumatol. 2015 Jul;67[7]:1688-99).
“I typically start with prednisone at 40 mg/day, and there’s a dramatic response in these patients. Then I taper them off after 2-3 months. If 2-3 months doesn’t put them into a long-term sustained remission, it’s time to go to something else,” said Dr. Stone.
So what’s the next move, then, after steroids fail? Dr. Stone was a pioneer in the strikingly successful use of B cell depletion via rituximab (Rituxan) in patients with IgG4-RD. First he and his coinvestigators demonstrated that this off-label use of rituximab led to rapid clinical and histologic improvement (Ann Rheum Dis. 2015 Jun; 74[6]:1171-7), then they showed it also causes levels of circulating plasmablasts, serum IgG4, and biomarkers of fibrosis to plunge, suggesting B cell depletion may halt the destructive process of collagen deposition that characterizes this immune-related disease (Ann Rheum Dis. 2015 Dec;74[12]:2236-43). They have also reported that patients with very elevated baseline serum IgG4 levels are at more than sixfold increased risk of relapse at a median of 244 days from their first rituximab infusion (Rheumatology [Oxford]. 2016 Jun;55[6]:1000-8).
The success with rituximab is just one example of how improved understanding of the pathophysiology of IgG4-RD has opened the door to novel treatments. Dr. Stone is the lead investigator in an ongoing phase II, open-label study in which 15 patients with active IgG4-RD will receive intravenous XmAb5871 every 2 weeks for 6 months to evaluate the effect on the IgG4-RD Responder Index. XmAb5871 is a monoclonal antibody that binds to CD19 and FCgammaRIIb in order to downregulate activated B cells and plasmablasts. It is also being developed for treatment of systemic lupus erythematosus.
Dr. Stone and his coinvestigators are working on a therapeutic approach to IgG4-RD that targets antigen presentation by activated B cells to CD4+ cytotoxic T cells at sites of disease. These CD4+ cytotoxic T cells contain signaling lymphocyte activation molecule F7 (SLAMF7) as a surface marker. Elotuzumab (Empliciti), an immunostimulatory humanized monoclonal antibody targeting SLAMF7, is already on the market for treatment of multiple myeloma, he noted.
Dr. Stone reported receiving IgG4-RD-related research funding from and serving as a consultant to Genentech and Xencor, which is developing XmAb5871.
