Macrophages are among the most important inflammatory cells in the synovium of patients with rheumatoid arthritis, according to research discussed at the Canadian Arthritis Research Conference: Research with Impact.
Dr. Jennifer Howitt Anolik
Work conducted as part of the Accelerating Medicines Partnership (AMP) Rheumatoid Arthritis and Systemic Lupus Erythematosus (RA/SLE) Network suggests that not only do macrophages play an inflammatory role, but there may also be a subset of macrophages that have a predominantly anti-inflammatory effect.
“These are cells that are really activated and can produce a lot of proinflammatory cytokines, including TNF [tumor necrosis factor],” said Jennifer Howitt Anolik, MD, PhD, associate professor of medicine at the University of Rochester (N.Y.) and cochair of the AMP RA/SLE Network.
“In addition to inflammatory mediators there’s an anti-inflammatory population which may control the disease,” she added, at the virtual meeting, which was sponsored by The Arthritis Society, the Canadian Rheumatology Association, and Canada’s Institute of Health and Arthritis.
There are up to 15 different populations of macrophages found so far as part of a project by Fan Zhang of Brigham and Women’s Hospital and Harvard Medical School in Boston, Dr. Anolik revealed. Of these, three have been shown to be proinflammatory and five have been shown to be anti-inflammatory – including one of particular interest that expresses MERTK, which recent work suggests are lacking in people with RA, compared with a control population of people with osteoarthritis (OA).
Clearly, Dr. Anolik said, there is “lots more work to do to understand how those anti-inflammatory monocytes might work, understand the relationship to treatment response and treatment failure, and how to target them.”
AMP RA/SLE Network: Examining RA synovial tissue
What’s unique about the AMP’s work is that it is involving single-cell analytics in which individual cells derived from patients with RA are subjected to an array of RNA sequencing and molecular classification methods.
“If we’re able to define the cells that are driving the disease at the tissue level, this may lead to better therapeutics and more of like a precision medicine approach,” Dr. Anolik said. An important feature of the AMP’s work is that it is based on the use of existing and thus “very informative cohorts” for whom we know a lot about disease characteristics, she said.
The AMP RA/SLE Network officially formed in 2014 and is a public–private partnership between the National Institutes of Health, the Food and Drug Administration, several biopharmaceutical companies, and nonprofit organizations. The task was to try to accelerate discoveries that would lead to better patient care.
“The initial phase [Research Phase 0], was really about developing the procedures in a standardized way,” Dr. Anolik said. “Because we’re looking at patient joint tissue samples, we needed to access that tissue and that required developing needle biopsy approaches.” Synovial biopsy had been pioneered in the United Kingdom and become fairly standard to perform, she added, but this was not an approach that was routinely being used in the United States at the time.
In the next step, Research Phase I, researchers looked at the expression profiles of RA synovial cells in a small group of patients. In all, around 5,000 cells from the joints of up to 20 patients with RA were analyzed. What was apparent was that while there were fibroblasts, monocytes, T cells, and B cells all present to some degree, there was substantial heterogeneity among those subtypes.
“Within all the different immune cells and stromal cells, we found 18 different populations overall,” Dr. Anolik said, giving some of the top-level findings. Both single-cell RNA sequencing and mass cytometry revealed that there were greatly (16-fold) increased numbers of a population of sublining fibroblasts and a 3.3-fold increase in interleukin-1-beta-expressing proinflammatory monocytes. There was a threefold increase in a subset of B cells expressing CD11/T-bet, and a 2.4-fold increase in certain peripheral T cells.
“Interestingly, we were able to pinpoint which cells are making which kinds of inflammatory mediators like inflammatory cytokines,” Dr. Anolik said. Notably, one of the fibroblast populations and one of the B cells were prominent producers of interleukin-6.
The AMP RA/SLE Network is now in Research Phase II, looking at much greater numbers of cells (>5,000) in more than 100 samples from individual patients. It’s a “very comprehensive, big data look at RA,” according to Dr. Anolik.
Research Phase II will also see more rigorous groups of patients being examined, including those who have not had any or much exposure to disease-modifying antirheumatic drugs and those who have inadequately responded to methotrexate or anti-TNF drugs.