Rituximab and COVID Shots: Studies Begin to Answer Key Questions

Jeff Craven

January 21, 2022

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Rituximab has presented something of a conundrum for patients taking the monoclonal antibody during the COVID-19 pandemic.

Used to manage a variety of autoimmune diseases and cancers, rituximab acts against CD20 proteins expressed on the surface of B cells, causing B-cell depletion. However, it is this B-cell depletion that may put these patients at greater risk of COVID-19 development, progression to more severe disease, and in-hospital mortality. Evidence for this appears to be mixed, with studies showing both that patients using rituximab to manage various diseases are and are not at increased risk for SARS-CoV-2 infection, COVID-19 progression, and mortality.

As COVID-19 vaccine rollouts take place across the world, more questions have been raised about the relationship between B-cell depletion from anti-CD20 therapies and COVID-19 vaccines. Do rituximab and other anti-CD20 therapies affect a patient's response to COVID-19 vaccines? If this is the case, does the timing of anti-CD20 treatment matter to maximize B-cell levels and improve the vaccine's effectiveness? And how do COVID-19 vaccine booster doses factor into the equation?

This article aims to summarize the latest research on how rituximab affects humoral and cell-mediated response following a COVID-19 vaccine primary series, and whether the addition of a COVID-19 vaccine booster dose changes patient response.

Humoral and Cell-Mediated Responses Following COVID-19 Vaccination

First, the bad news: The vaccine is unquestionably safe to administer in patients taking rituximab, but one thing that has been well established is that antibody response to COVID-19 vaccination in these individuals does is reduced. This isn't entirely unprecedented, as previous studies have shown a weakened immune response to pneumococcal polysaccharide and keyhole limpet hemocyanin vaccines among patients taking rituximab.

Dr Robert Spiera

"Compromised immunogenicity to the SARS-CoV-2 vaccines has been demonstrated in rituximab-treated patients, which is of particular concern given the observation that B-cell–depleting therapies may be associated with worse COVID outcomes," Robert F. Spiera, MD, director of the Scleroderma, Vasculitis, and Myositis Center at the Hospital for Special Surgery in New York, said in an interview.

For example, in a recent study from the Medical University of Vienna, 29 (39%) of 74 patients receiving rituximab (43% as monotherapy, 57% with conventional-synthetic disease-modifying antirheumatic drugs) who were vaccinated with either the Comirnaty (Pfizer-BioNTech) or Spikevax (Moderna) COVID-19 vaccine achieved seroconversion, compared with 100% of patients in a healthy control group, and all but 1 patient without detectable CD19+ peripheral B cells did not develop anti–SARS-CoV-2 receptor-binding domain antibodies.

Dr Ingrid Jyssum

"There is an increasing number of studies in this field, and they confirm that patients treated with rituximab and other anti-CD20 agents have severely reduced serological responses to COVID-19 vaccines," Ingrid Jyssum, MD, of the division of rheumatology and research at Diakonhjemmet Hospital in Oslo, said in an interview.

One silver lining is that patients treated with anti-CD20 therapies appear to have a cell-mediated response following vaccination even if they don't develop SARS-CoV-2 antibodies. "Studies that also investigate T-cell responses are starting to emerge, and so far, they show that, even if the patients do not have antibodies, they may have T-cell responses," Jyssum said.

One study of 24 patients with autoimmune diseases taking rituximab that evaluated humoral and T-cell responses following vaccination with the Comirnaty vaccine found that none had a humoral response to the vaccine, but the T-cell response from that group did not significantly differ from 35 patients receiving other immunosuppressants and 26 patients in a healthy control group. In another study of rituximab- or ocrelizumab-treated patients who received mRNA-based COVID-19 vaccines, 69.4% developed SARS-CoV-2–specific antibodies, compared with a control group, but 96.2% of patients taking ocrelizumab and 81.8% of patients taking rituximab mounted a spike-specific CD8+ T-cell response, compared with 66.7% in the control group, and there were comparable rates (85%-90%) of spike-specific CD4+ T cells in all groups. In the study from the Medical University of Vienna, T-cell response was detected in rituximab-treated patients who both did and did not mount an antibody response.

The clinical relevance of how a blunted humoral immune response but a respectable T-cell response to COVID-19 vaccines affects patients treated with anti-CD20 therapies isn't currently known, Jyssum said.

While these data are reassuring, they're also incomplete, Spiera noted. "The ultimate outcome of relevance to assess vaccine efficacy is protection from COVID and from severe outcomes of COVID infection (i.e., hospitalization, mechanical ventilation, death). That data will require assessment of very large numbers of rituximab-treated vaccinated patients to be compared with rituximab-treated unvaccinated patients, and is unlikely to be forthcoming in the very near future.

"In the meantime, however, achieving serologic positivity, meaning having evidence of serologic as well as cellular immunity following vaccination, is a desired outcome, and likely implies more robust immunity."

Does Treatment Timing Impact COVID-19 Vaccine Response?

Given enough time, B-cell reconstitution will occur in patients taking rituximab. With that in mind, is it beneficial to wait a certain amount of time after a patient has stopped rituximab therapy or time since their last dose before giving them a COVID-19 vaccine? In their guidance on COVID-19 vaccines for patients with rheumatic and musculoskeletal diseases, the American College of Rheumatology said there is moderate evidence to consider "optimal timing of dosing and vaccination with the rheumatology provider before proceeding."

"Guidelines and preliminary studies of serologic response to COVID vaccine in rituximab-treated patients have suggested that longer time from last rituximab exposure is associated with a greater likelihood of a serologic response," Spiera said.

In a brief report published in Arthritis & Rheumatology, Spiera and colleagues performed a retrospective chart review of 56 patients with varying levels of last exposure to rituximab who received a COVID-19 vaccine. Their results showed that, when patients were vaccinated 6-12 months after the last rituximab dose, 55% were seronegative, and when this was more than 12 months, only 13% were seronegative, compared with seronegativity in 86% who were vaccinated less than 6 months after their last rituximab dose.

The RituxiVac trial, conducted by researchers in Switzerland, also examined vaccine responses of 96 rituximab-treated patients who received Comirnaty or Spikevax; results recently published in The Lancet Rheumatology showed findings similar to other studies, with reduced humoral and cell-mediated responses. In the RituxiVac trial, the median time to last anti-CD20 treatment was 1.07 years.

"The typical interval between rituximab doses [for treatment of rheumatoid arthritis, as well as for remission maintenance in antineutrophil cytoplasmic antibody–associated vasculitis] is typically 6 months, and this has become widely used as the interval from last rituximab to time of COVID vaccination, with a recommendation to wait 4 weeks (if possible) from time of vaccination until the next rituximab administration," Spiera explained. However, this window seems to vary depending on the study.

Recent research published in Arthritis & Rheumatology indicates B-cell levels could be a relevant indicator for humoral and cell-mediated response in patients with rheumatic diseases treated with rituximab, with a level of 10 B cells/mcL (0.4% of lymphocytes) identified as one potential marker for likely seroconversion following COVID-19 vaccination.

"In some smaller case series, it has been further recognized that rituximab-treated patients who were beginning to reconstitute peripheral B cells were most likely to respond serologically. Our present study confirmed those findings, demonstrating that the presence of detectable B cells was strongly associated with vaccine responsiveness, and affords complementary information to time from last [rituximab dose] in informing the likelihood of a vaccine response," Spiera said.

However, the literature is limited in this area, and an exact cutoff for B-cell counts in these patients isn't currently known, Jyssum said. A better metric is time away from anti-CD20 therapies, with CD19 cell count being highly correlated with last infusion.

Spiera agreed that there is no consistent B-cell percentage that works as a cutoff. "In our study, we looked at it as a binary variable, although we did find that a higher percentage of B cells in the peripheral lymphocyte population was associated with a higher likelihood of seroconversion. We did not, however, identify a 'threshold' for vaccine serologic responsiveness."

Should Clinicians Measure Antibodies?

The Food and Drug Administration and the Centers for Disease Control and Prevention have recommended that health care providers and the public not use COVID-19 antibody tests as a way to gauge immunity after exposure to SARS-CoV-2 and after receiving a COVID-19 vaccination. The ACR's guidance on COVID-19 vaccination for patients with rheumatic and musculoskeletal diseases strongly recommends against ordering antibody tests for patients with autoimmune inflammatory rheumatic diseases as a way to measure immunity.

"Generally, such measurements are not recommended as the clinical correlate of various antibody levels are not known," Jyssum said. "With regular infusions of rituximab or other anti-CD20 agents, one cannot expect that these patients will develop significant levels of antibodies."

However, she said there might be situations where it's useful to know whether a patient has developed antibodies at all. "Assessing the significance of specific antibody levels is difficult, and the subject of scientific studies. Patients lacking a humoral vaccine response are left to rely on their T-cell responses and on infectious control measures to prevent disease."

Spiera said he disagreed with guidelines recommending against checking antibody levels after vaccination, "particularly in patients treated with immunosuppressive medications that might be expected to blunt their serologic response to the vaccines.

"Although we cannot be sure what level of measurable antibodies offer what level of protection, most clinicians would agree that patients who demonstrate no detectable antibodies (which is a common finding in rituximab-treated patients) should be considered at higher risk," he said. "Indeed, recommendations regarding booster vaccine administration in general was initially based on the observation of declining antibody levels with longer time from vaccination."

Do COVID-19 Vaccine Boosters Help Patients on Anti-CD20 Therapy?

As of January 2022, the FDA and CDC have recommended a third primary series shot of COVID-19 vaccines for some moderately to severely immunocompromised patients as young as 5 years old (for Comirnaty vaccine) or a booster shot of either Comirnaty or Spikevax for everyone aged 12 years and older, including immunocompromised people, while the ACR goes into more detail and recommends clinicians time a patient's booster shot with temporary treatment interruption.

In The Lancet Rheumatology, Jyssum and colleagues recently published results from the prospective Nor-vaC study examining the humoral and cell-mediated immune responses of 87 patients with RA being treated with rituximab who received the Comirnaty, Spikevax, or Vaxzevria (AstraZeneca) COVID-19 vaccines; of these, 49 patients received a booster dose at a median of 70 days after completing their primary series. The results showed 19 patients (28.1%) had a serologic response after their primary series, while 8 of 49 patients (16.3%) who received their booster dose had a serologic response.

All patients who received a third dose in the study had a T-cell response, Jyssum said. "This is reassuring for patients and clinicians. T cells have been found to be important in countering COVID-19 disease, but whether we can rely on the T-cell response alone in the absence of antibodies to protect patients from infection or from serious COVID disease is still not determined," she said.

When asked if she would recommend COVID-19 vaccine booster doses for patients on rituximab, Jyssum replied: "Absolutely."

Another study, recently published in Annals of the Rheumatic Diseases, examined heterologous and homologous booster doses for 60 patients receiving rituximab without seroconversion after their COVID-19 vaccine primary series. The results showed no significant difference in new seroconversion at 4 weeks based on whether the patient received a vector or mRNA vaccine (22% vs. 32%), but all patients who received a booster dose with a vector vaccine had specific T-cell responses, compared with 81% of patients who received an mRNA vaccine booster. There was a new humoral and/or cellular response in 9 of 11 patients (82%), and most patients with peripheral B cells (12 of 18 patients; 67%) achieved seroconversion.

"Our data show that a cellular and/or humoral immune response can be achieved on a third COVID-19 vaccination in most of the patients who initially developed neither a humoral nor a cellular immune response," the researchers concluded. "The efficacy data together with the safety data seen in our trial provide a favorable risk/benefit ratio and support the implementation of a third vaccination for nonseroconverted high-risk autoimmune disease patients treated with B-cell–depleting agents."

Spiera said booster doses are an important part of the equation, and "it is important to consider factors that would be associated with a greater likelihood of achieving a serologic response, particularly in those patients who did not demonstrate a serologic response to the initial vaccines series.

"Preliminary data shows that the beginnings of B-cell reconstitution is also associated with a positive serologic response following a booster of the COVID-19 vaccine," he said.

The authors of the cited studies reported numerous relevant financial disclosures. Spiera and Jyssum reported no relevant financial disclosures.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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