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B-cell level may affect COVID booster efficacy in MS


Patients with multiple sclerosis (MS) treated with the B-cell-depleting medication rituximab who have not yet been vaccinated against COVID-19 should get the initial vaccination as soon as possible but wait to get a booster shot until B-cell levels increase, new research suggests.

In a prospective cohort study, 90% of patients taking rituximab whose B-cell level was at least 40 cells/mcL had a sufficient antibody response to the Pfizer vaccine, whereas among those with lower levels, the antibody response was significantly lower.

Results also showed a wide variation in the length of time needed for adequate B-cell restoration. Some patients needed a year or longer for levels to become adequate.

The findings led the hospital where the study was conducted to suspend rituximab therapy until patients could be vaccinated. The findings also prompted researchers to call for new guidelines on vaccine scheduling that are based on B-cell levels and not on the current criteria of length of time since last treatment.

“It’s meaningless to just go by some recommendation covering time since the last treatment,” study investigator Joachim Burman, MD, PhD, a consultant neurologist at Uppsala University Hospital and an associate professor at Uppsala University, both in Sweden, told this news organization.

“It’s misleading and potentially harmful for patients,” Dr. Burman said.

The findings were published online in JAMA Network Open.

Finding the cutoff

Drugs such as rituximab target CD20, a protein found on the surface of B cells, resulting in B-cell depletion.

Rituximab is the most common MS therapy used in Sweden. The drug is approved in the United States to treat rheumatoid arthritis and some forms of cancer, but it is not approved for treatment of MS.

Prior research showed that antibody response to COVID-19 vaccines was lower in patients receiving B-cell therapy than in the general population. That was not altogether surprising, given the fact that studies have found a similarly weakened antibody response to other vaccines.

But before now, there was no known B-cell threshold sufficient to mount an acceptable antibody response following COVID vaccination.

Researchers enrolled 67 patients in the study. Of those patients, 60 had received rituximab treatment, and seven had not.

Approximately 6 months after the last rituximab dose, the B-cell count was lower than 10/mcL for 40% of patients. In that group, rituximab treatment duration was the only factor significantly associated with slower B-cell mobilization (median duration, 4.0 years, vs. 2.1; P = .002).

Close monitoring needed

Six weeks after vaccination with tozinameran, the mRNA vaccine manufactured by Pfizer, 28% of patients failed to generate a sufficient antibody response. Among those patients, the median B-cell count was 22/mcL, versus 51/mcL for the remainder of the cohort (P < .001).

A cutoff value of 40/mcL rendered adequate levels of anti-spike immunoglobulin G antibodies in 90% of patients and a strong response in anti-RBD antibodies in 72%.

Study participants did register an adequate T-cell response to the vaccine, suggesting at least some level of protection.

Because MS patients are at increased risk for serious illness from SARS-CoV-2 infection, the investigators recommend that patients with MS receive their initial COVID vaccines as soon as possible – but that they should hold off on receiving a booster until their B-cell counts reach 40/mcL.

Regarding when a clinician should re-vaccinate, “the results from our study strongly suggest that you should not do that right away or just follow some generic guideline,” Dr. Burman said.

“You should closely monitor the B-cell values, and re-vaccinate once those B- cells hit the level of 40 cells/mcL” he added.

Dr. Burman said he would expect that their findings would hold with the other mRNA vaccine and with any other B-cell therapy.


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