CHICAGO – A positive B cell clonality test in a peripheral blood sample predicts imminent onset of rheumatoid arthritis with a high degree of accuracy in at-risk individuals, Niek de Vries, MD, PhD, reported at the annual meeting of the American College of Rheumatology.
This finding, now confirmed twice over in separate validation studies, opens the door to trials of pharmacologic treatment aimed at preventing rheumatoid arthritis (RA).
“In my view, a positive test might be an indication for preventive treatment and retesting at 1 year to evaluate the treatment effect,” said, professor of rheumatology at the University of Amsterdam.
Many patients with RA experience a pre-RA phase marked by joint pain, the presence of RA-specific autoantibodies, IgM rheumatoid factor, and/or anticitrullinated protein antibodies, but no synovial inflammation. The challenge in attempting to develop RA preventive strategies targeting this population is that only about 28% of them go on to develop RA within 3 years. Exposing the entire preclinical-phase population to powerful antirheumatic drugs to try to prevent RA in the minority who are actually headed for overt disease is not an attractive strategy.
That’s why Dr. de Vries and his coinvestigators developed a method of B cell receptor (BCR) analysis using PCR and next-generation sequencing techniques. They determined that when a clone comprised more than 0.5% of the total B cell receptor population, it can be considered an expanded or dominant clone. They then demonstrated that when a patient in the pre-RA phase has five or more dominant clones in a peripheral blood sample, that can be considered a positive BCR test. In two published studies, they showed that a positive BCR test in the pre-RA stage accurately predicts onset of overt RA within the next several years (and ). They have also shown that at the time of RA onset, the BCR clones disappear from peripheral blood and reappear in the synovium.
At the ACR annual meeting, Dr. de Vries presented the results of a new BCR test validation, this one involving 129 pre–RA-phase Dutch patients. The purpose of this study was to learn whether the BCR test is more predictive than clinical predictors such as the Risk Rule Model, and also to determine whether a higher number of dominant clones predicts RA onset even more accurately than the five-or-more clone threshold the investigators had been using. The answer to both questions proved to be yes.
Thirty-five percent of the 129 pre-RA subjects had a positive BCR test as defined by the presence of five or more expanded clones. A total of 75% of them went on to develop RA within the next 3 years. None of the BCR test-negative patients did. That result translated to a test sensitivity of 100%, a specificity of 87%, a positive predictive value of 71%, and a negative predictive value of 100%. A positive BCR blood test was associated with a 120-fold increased risk of an RA diagnosis within 3 years.
The investigators also compared outcomes in the 17% of study participants with a high degree of BCR test positivity, defined as the presence of nine or more expanded clones, versus the 18% of subjects whose positive BCR test had five to eight clones. Overall, 91% with a highly positive BCR test featuring nine or more clones developed RA within 3 years, compared with 55% of those with five to eight clones.
These findings permit categorization of pre-RA patients into three groups. Those with a negative BCR test can be reassured that their 3-year risk of developing RA is similar to the background risk in the general population. Those with a mid-range positive BCR test – that is, five to eight dominant clones – should probably be retested periodically, although the optimum interval is still under study. And patients with a highly positive BCR test might be candidates for preventive therapy.
Before RA-preventive therapy during the high-risk pre-RA phase can be introduced into routine clinical practice, however, several issues need to be resolved, Dr. de Vries continued. Although a single dose of rituximab (Rituxan) showed efficacy in a proof-of-concept study, that was off-label therapy. There is as yet no approved agent for prevention of RA in high-risk patients. Also, the risk/benefit ratio of preventive therapy will need to be determined. And rheumatologists will have to figure out how to identify these high-risk pre-RA individuals early, when preventive therapy is likely to most effective.
Several audience members observed that the Dutch investigators’ BCR test using PCR and next-generation sequencing is technically complex. They asked if the BCR results might correlate with any far more readily available serologic tests. The answer is no, according to Dr. de Vries.
“I think it’s very important to realize that what we test is the migration of B cells or plasmablast-like cells through the blood at the moment that we’re testing. This is completely different from a serological assessment of antibody production by plasma cells which are present in the bone marrow, which changes very little despite effective treatment. In contrast, if we test B cell migration while a patient gets corticosteroids we see an immediate disappearance of all these cells. So it’s a different parameter,” the rheumatologist explained.
The Dutch Arthritis Association funded the study. Dr. de Vries noted that he is a coinventor of the BCR test, the intellectual property rights for which belong to the University of Amsterdam. He receives research funding from Pfizer, Roche, Janssen, and GlaxoSmithKline.
SOURCE: de Vries N et al. Arthritis Rheumatol. 2018;70(Suppl 10). .