Anti-CD20 monoclonal antibodies, like rituximab, have enhanced the outcomes of B-cell lymphoma patients when incorporated into many standard chemotherapy regimens (1). However, a significant advancement was achieved with the introduction of maintenance approaches. These involve periodic infusions of anti-CD20 monoclonal antibodies every 2, 3 or 6 months, ensuring continuous anti-CD20 activity against the minimal residual disease that remains after an initial debulking immunochemotherapy. The use of anti-CD20 maintenance approaches has improved the outcome in terms of longer progression-free (PFS) or overall survival (OS) in B-cell lymphomas such as follicular or mantle lymphoma, as shown in PRIMA (2, 3), BRIGHT (4) or LYMA (5) trials. However, other anti-CD20 monoclonal antibodies, such as obinutuzumab, showed better efficacy results, being able to rescue rituximab-resistant patients but at the cost of greater toxicity (6, 7).

Although anti-CD20 maintenance is generally well-tolerated, there is still some significant toxicity mainly related to peripheral B-cell depletion. This B-cell aplasia is generally complete during anti-CD20 maintenance and, after the last dose of anti-CD20, B-cell counts may need several months to recover or even remain prolonged or persistent in some individuals (8). This may impair serological response to neoantigens, including SARS-CoV-2 spike glycoprotein within SARS-CoV-2 vaccines (9) and, although this is well described, to the best of our knowledge no specific study has focused on patients receiving anti-CD20 maintenance approaches increasing the risk of prolonged B-cell aplasia. At the same time, the COVID-19 pandemic offered us the opportunity to study the vaccine response to a particular neoantigen, related to SARS-CoV-2 virus. In this study, we aim to analyze the effect of anti-CD20 maintenance on SARS-CoV-2 vaccine responses and COVID-19 incidence and severity in a single reference hospital.

We present the first data set about the impact on SARS-CoV-2 vaccines efficacy of a particular approach in anti-CD20 therapy for B-cell malignancies, the maintenance treatment. Most anti-CD20 maintenance approaches imply a severe long-term (2-3 years) B-cell ablation. This fact has generated important concerns about their safety in the context of the SARS-CoV-2 pandemic to both physicians and patients. Such concerns may lead to preclude the use of these anti-CD20 maintenance, which consequently may imply a worse control of the B-cell malignancy.

Anti-CD20 therapy efficiently depletes peripheral B-cells that represent only 2% of the total B-cell population. Similarly, there is an impact on peripheral lymphoid tissues but lower on long-lived plasma cells, which do not express the anti-CD20 antigen (12–15). After short-term anti-CD20 induction schemes, such as R-CHOP-like regimens or rituximab monotherapy, the peripheral blood B-cell compartment has been described to recover within 6-9 months after the last anti-CD20 dose (8, 12). However, there is less information regarding long-term anti-CD20 approaches such as anti-CD20 maintenance, but this data could be obtained evaluating a surrogate biomarker of proper B-cell function such as seroconversion after vaccination. To identify the point in which there is a significant change in the ability of seroconvert after vaccination, we evaluated only patients who receiving, or had previously received, anti-CD20 maintenance as part of their frontline therapy. We excluded those who received anti-CD20 maintenance in the second or subsequent treatment lines (Figure 1).

In our study, to our knowledge also for the first time, we used ROC curves to calculate the length of main impairment of seroconversion after vaccination in anti-CD20 maintenance approaches: 24 months since the last anti-CD20 dose. The median rate of vaccination failure was 31% in our series, being even higher (64%) during maintenance and up to the first 24 months after the last dose of anti-CD20 maintenance. Beyond this moment, the seroconversion rate improved until 90% (10% vaccination failure rate), showing a much longer impairment on B-cell function after anti-CD20 maintenance therapy compared to short induction regimens.

A recent metanalysis in patients mostly receiving short courses of anti-CD20 therapy, reported even lower seroconversion rates for 2 doses of the pandemic influenza vaccine in patients on active anti-CD20 therapy (12%) and that apparently improved with the time since the last anti-CD20 dose. When comparing patients on active anti-CD20 therapy with controls, the differences in seroconversion rates were less pronounced by an average of 6 to 12 months from last anti-CD20 dose and were similar beyond 12 months (16). To overcome this prologued time to seroconversion it has been proposed to delay anti-CD20 therapy until after vaccination (17). Another recent study proposed that the optimal interval for SARS-CoV-2 vaccination after the final dose of anti-CD20 is 5.5 months, but mostly in patients receiving short courses of anti-CD20 therapy (18).

In the context of our study on SARS-CoV-2 serologic assessment, the high sensitivity and specificity of the CLIA method is especially crucial, ensuring that the antibody responses of individuals, even if weak, are accurately captured. This ensures the validity and robustness of our findings, particularly when drawing conclusions about the impact of treatments or interventions on antibody production and response (19).

The other interesting contribution that we can extract form our series is that anti-CD20 maintenance approaches are safe even in patients with a high degree of humoral immunodeficiency during especially risky situations such as the recent SARS-CoV-2 pandemic. In our patients we had no significant impact on survival of seroconversion failure after SARS-CoV-2 vaccination or hypogammaglobulinemia. However, 25% of these patients received intravenous immunoglobulins therapy, mainly those having symptomatic hypogammaglobulinemia (59%). Patients receiving anti-CD20 maintenance approaches have an increased risk of hypogammaglobulinemia, some of them associated with recurrent infections (20). Some guidelines recommend administering intravenous immunoglobulins to patients with 2 or more non-neutropenic infections in a 6-month period of time (21) and this is also our standard approach. Furthermore, in our series all patients were vaccinated. It is well described that even patients who do not respond to the SARS-CoV-2 vaccines, may develop some degree of T-cell sensibilization that could in part protect or reduce the severity of COVID19 (22).

Another aspect warranting discussion involves the controversial impact of induction immunochemotherapy based on bendamustine (BR) compared to alternatives such as R-CHOP/R-CVP or other options. In our study, we noted a higher incidence of COVID-19 among patients treated with BR, potentially attributable to a higher immunosuppressive activity of bendamustine but also to its status as the preferred therapy for the most recent indolent lymphoma cases, and the corresponding shorter interval since the last anti-CD20 dose. However, it is pivotal to highlight, as previously mentioned, that this increased incidence of COVID-19 did not correlate with a higher incidence of severe COVID-19, shorter OS or higher COVID-19-specific death rates.

Like all retrospective studies, our work is subject to potential bias. Furthermore, we included only those patients who were alive in May 2022, a time when less aggressive SARS-CoV-2 variants were in circulation. Although the impact of these variants might be partially compensated by the less stringent lockdown measures in place, they could have influenced the OS analysis. However, these factors would not affect the seroconversion rates.

Although in our series, vaccination failure or hypogammaglobulinemia did not impact outcomes, COVID19 still had a small but significant effect on mortality (2.5%) and OS. While this percentage is low when looking at the entire series, it is higher for cases that were severe or required ICU admission (13% and 17%, respectively). However, these figures do not significantly differ from the rates reported for the general immunocompetent population (23, 24). They still represent acceptable mortality rates considering the potential B-cell immunosuppression in this group of patients. Given this, we can hypothesize that with the above-mentioned prophylactic measures and close monitoring, there is no justification to broadly preclude the use of anti-CD20 maintenance to any of the well-demonstrated clinical settings in which these approaches have shown important benefit in terms of progression-free survival or even lymphoma cure. Additionally, during the COVID-19 pandemic several anti-SARS-CoV-2 monoclonal antibodies, such as cilgavimab/tixagevimab (25) or sotrovimab (26) have been developed that could help to compensate anti-CD20 maintenance-associated humoral immunodeficiency.

We conclude that anti-CD20 maintenance therapy impairs serological responses to SARS-CoV-2 vaccines. To our knowledge we report for the first time that patients during maintenance and up to 24 months after finishing the last anti-CD20 dose are at a higher-risk of vaccine failure and more severe cases of COVID-19. However, a close monitoring, intravenous immunoglobulin supplementation, if necessary, proper vaccination if available or the use of specific monoclonal antibodies in the case of COVID-19 infection, may overcome the impact on survival of this lack of serological response in high-risk population. In other words, with these measures, anti-CD20 maintenance is a safe procedure that should not be avoided or discontinued even in the case of hypogammaglobulinemia.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by Balearic Islands ethic committee. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

AG: Conceptualization, Formal Analysis, Investigation, Methodology, Supervision, Validation, Writing – original draft, Writing – review & editing. AA: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Validation, Writing – original draft, Writing – review & editing. MG-R: Conceptualization, Formal Analysis, Investigation, Validation, Writing – original draft, Writing – review & editing. SP: Data curation, Resources, Validation, Writing – review & editing. LG-M: Data curation, Resources, Validation, Writing – review & editing. JM-S: Data curation, Investigation, Resources, Validation, Writing – review & editing. TR: Data curation, Investigation, Resources, Validation, Writing – review & editing. MG-G: Data curation, Investigation, Methodology, Supervision, Validation, Writing – review & editing. JF: Conceptualization, Data curation, Methodology, Supervision, Writing – review & editing. OV: Data curation, Methodology, Supervision, Validation, Writing – review & editing. RA: Data curation, Methodology, Validation, Writing – review & editing. ASl: Conceptualization, Methodology, Supervision, Validation, Writing – review & editing. ASm: Data curation, Resources, Validation, Writing – review & editing. LB: Data curation, Resources, Validation, Writing – review & editing.