Rituximab treatment of ANCA-associated vasculitis
Loïc Raffray1 and Loïc Guillevin2

1Department of Internal Medicine, Félix-Guyon University Hospital of La Réunion, CS11021, Saint-Denis, Reunion Island, France;
2Referral Center for Rare Systemic and Autoimmune Diseases, Department of Internal Medicine, Hôpital Cochin, Université Paris Descartes, Paris, France

CONTACT Loïc Guillevin, Tel: +3360835763 [email protected] ORCID (Open Researcher and Contributor ID): 0000-0001-6463-2160


Introduction: Rituximab, an anti–B-cell biological therapy, has been investigated in several clinical trials on antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs).
Areas covered: In this paper, the clinical trials and open-label studies on rituximab efficacy and safety in treating AAVs are reviewed.
Expert opinion: Rituximab achieved high remission-induction and sustained- maintenance rates for patients with these severe diseases, thereby challenging the cornerstone treatment of corticosteroids and cyclophosphamide followed by azathioprine. Rituximab should be used as first-line therapy with corticosteroids to

induce remission of severe AAVs, especially in situations in which cyclophosphamide may be problematic (relapse after cyclophosphamide, women of childbearing age, risk of malignancy). Cyclophosphamide indications are likely to be restricted in the future. Whenever possible, rituximab should be preferred to azathioprine to maintain
remission. The current maintenance regimen has been extended to at least 18 months but its optimal duration remains unknown and recent data suggest the possibility to extend treatment to 4 years. Future challenges include defining the best dose regimen: at present, different schedules are used as alternatives to those recognized as standards by health authorities. In addition, it remains to identify which patients will benefit the most from long-term retreatment: potentially those with relapsing disease or anti- proteinase-3 ANCA-positivity.


ANCA; B lymphocytes; rituximab; therapeutic monoclonal antibodies; vasculitis; granulomatosis with polyangiitis; microscopic polyangiitis; eosinophilic granulomatosis with polyangiitis

Article highlights

•B cells participate in the pathophysiology of ANCA-associated vasculitides (AAVs).
•The anti–B-cell biological therapy rituximab has been evaluated in several published randomized–controlled trials on AAVs, and is currently being assessed to treat eosinophilic granulomatosis with polyangiitis.

•To induce remission of severe flares, rituximab is not inferior to the historical reference treatment of sequential corticosteroids and cyclophosphamide then azathioprine.
•For remission-maintenance therapy, rituximab is superior to azathioprine, the historical reference.
•Further studies are needed to optimize rituximab regimens for remission induction and maintenance of severe and perhaps non-severe AAV flares.



Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) are a group of systemic necrotizing vasculitides involving small-sized vessels [1], with variable ANCA presence. AAVs comprise three distinct diseases: granulomatosis with polyangiitis (GPA, formerly Wegener’s granulomatosis), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg–Strauss syndrome). Although heterogeneous, these entities share common pathophysiological mechanisms, clinical and biological characteristics at onset, and therapeutic strategies. Pharmacological treatment relies mainly on corticosteroids (CS) and, for most vasculitides, the adjunction of an immunosuppressant, e.g., cyclophosphamide,
methotrexate, azathioprine or mycophenolate mofetil. That strategy was associated with improved survival [2–5], despite high morbidity, mainly attributable to infections and malignancies [6–8].
Targeted therapies have been evaluated with the aim of enhancing efficacy with fewer adverse events (AEs). During the past decade, conventional immunosuppressants have been challenged by rituximab. Initially prescribed to treat B-cell lymphoma, this anti–B-cell therapy has also been reported to be effective against various autoimmune disorders, e.g., rheumatoid arthritis and immune thrombocytopenia [9]. Growing interest in the group of autoimmune vasculitides among AAVs led to the first large-scale randomized–controlled trials (RCTs) of a biological therapy for AAVs.
Herein, we review rituximab regimens for AAV therapy, results obtained in AAV patients for the two treatment steps: remission-induction and -maintenance, according to evidence obtained in the trials, and this biological agent’s impact on current and future therapeutic strategies.

1.1.Pathophysiology of AAVs

First, to understand treatment strategies comprising rituximab, some background information in required.
AAVs share some common characteristics, for example, ANCA-positivity [1]. ANCA are thought to play a key role in AAV pathophysiology, through eosinophil and neutrophil activation and complement-component involvement, finally leading to vessel and tissue damage [10]. Other cell subsets are also involved, such as B and T cells, that amplify the inflammatory loop. The results of several studies highlighted B-cell participation in AAV pathogeneses: these immune cells are activated during disease flares and granulomas contain activated B cells [11–13]. B cells will differentiate into plasma cells, the producers of ANCA. Those findings indicated a potential benefit of
therapies targeting B lymphocytes. Even though the name AAV indicates ANCA presence, their positivity rates vary widely, ranging from 30% to 90% of the patients, depending on the disease entity [14–16]. This variability reflects the heterogeneous pathways culminating in vasculitis, and the need for better understanding of the mechanisms involved to optimize the use of more specific and targeted treatments.
Importantly, because a prominent eosinophil role in EGPA pathophysiology was alleged [17], patients with EGPA were excluded from most early trials on AAVs, like the pivotal RCTs on rituximab for GPA and MPA. The French Vasculitis Study Group (FVSG) has designed prospective trials to evaluate rituximab for induction of EGPA remission and its maintenance [18,19].

1.2.AAV evolution and disease severity

AAVs are characterized by a high relapse risk, reaching up to 60% at 5 years, after achieving remission with prednisone combined with conventional immunosuppressants (i.e., cyclophosphamide for induction, followed by azathioprine or methotrexate or mycophenolate mofetil) [14,20,21]. The relapse-risk and mortality rates are higher for GPA patients, especially those with severe disease, which implies that treatment should be adapted to disease severity, as needed, usually requiring treatment prolongation for patients at risk of relapse. Such therapeutic decisions imply knowledge of factors predictive of relapse. Clinical GPA relapses are more frequent (>50% at 5 years) than for MPA or EGPA (around 40–50% each) [20–22]. The GPA-relapse rate is also affected by the presence of anti-proteinase-3 (PR3) or anti-myeloperoxidase (MPO) ANCA at diagnosis and during follow-up. It was shown that relapses were more frequent when patients were anti-PR3-positive than anti-MPO-positive or ANCA-negative [23,24].
Because of its severity and high risk of relapse, systemic GPA must be treated with CS and the adjunction of an immunosuppressant or rituximab. For patients with EGPA or MPA, treatment choice depends on disease severity, which can be assessed with standardized severity scores, such as the Five-Factor Score (FFS) or the Birmingham Vasculitis Activity Score (BVAS) [25,26]. Other factors must be taken into consideration to make treatment decisions: patient age and comorbidities. For example, for patients over 65 years requiring an immunosuppressant, lower cyclophosphamide doses can be prescribed and obtain comparable efficacy [27].

1.3.Treatment strategies

The therapeutic approach is divided into two phases: remission-induction and

-maintenance regimens. Treatment of a disease flare aims at obtaining prompt remission, so as to avoid disease-related morbidity and mortality. During the induction phase, treatment should be adapted to disease severity. The induction phase usually lasts 4–6 months. Once remission has been achieved, the goal is to sustain it as long as possible without relapse; maintenance therapy usually lasts at least 18 months.
Until the early 2010s, therapeutic strategies relied mostly upon CS and conventional immunosuppressants. For non-severe disease, CS were used alone as first-line therapy [28] to treat MPA and EGPA, and immunosuppressants were added when CS-resistance or early relapse occurred after remission [29]. For all GPA patients and MPA or EGPA patients with poor-prognosis factors, induction therapy usually comprised CS and cyclophosphamide. Cyclophosphamide is mostly administered as intravenous pulses but the oral route is also prescribed by some clinicians and persists in international recommendations [30]. Conventional therapy can obtain a remission rate of 70%–80% at 6 months. Once remission has been attained, the usual maintenance regimen combined CS tapering and an immunosuppressant, like azathioprine or methotrexate.


In early 2020, the following marketed biosimilars are available, depending on the country: AcellBia, Blitzima, Ritemvia, Rituzena, Rixathon, Riximyo and Truxima. Rituximab is a monoclonal mouse–human chimeric anti-CD20 IgG1 antibody that induces depletion of mature and memory B cells, via an apoptotic process mediated by antibody- and complement-dependent cytotoxicity. Although the exact mechanisms of rituximab efficacy are still unelucidated, it is hypothesized that abrogation of autoreactive
antibody production is fundamental. Other explanations may be possible, e.g.,

prevention of antigen presentation by B cells [11]. The agent is usually administered intravenously, along with methylprednisolone, acetaminophen and antihistamine to prevent immediate infusion reactions. Two main schemes are used to induce remission of autoimmune diseases: an infusion of 375 mg/m2 of body-surface area once weekly for
4weeks or 2 1-g infusions 2-weeks apart. B-cell depletion usually lasts at least 6–8 months in the majority of patients, and up to 18 months in fewer than 10% of the recipients. Retreatment regimens for maintenance use lower doses, frequently a single 500-mg pulse. No specific recommendation has been formulated concerning dose adjustments for patients with renal insufficiency. So far, biosimilars have been tested mainly against B-cell lymphomas and solely rheumatoid arthritis among connective tissue diseases [31].


Our search strategy consisted of an extensive Medline review of the literature using the following MESH items: anti-neutrophil cytoplasmic antibody-associated vasculitis, microscopic polyangiitis, granulomatosis with polyangiitis, Churg-Strauss syndrome, treatment, rituximab, randomized controlled trial, clinical trial, guidelines. We also reviewed literature combining rituximab and anti-neutrophil cytoplasmic antibody, safety, drug-related side effects, adverse reactions, pregnancy, infections, agammaglobulinemia or hypogammaglobulinemia, neoplasms. We reviewed the references included in the identified articles and abstracts from recent congresses.

42.1.Rituximab efficacy against AAVs

The first prospective, open-label, pilot trial on rituximab to treat AAVs included 10 GPA

patients [32]. All of them received a weekly infusion of 375 mg of rituximab/m2 for 4 weeks (as for lymphomas) in conjunction with CS. At 6 months, all patients had achieved clinical remission, as assessed with BVAS. Subsequently, rituximab efficacy was described in several small, non-controlled studies and case series [33–37], whose patients manifested various clinical signs (ear, nose & throat (ENT), ophthalmological, renal, pulmonary, systemic involvements) of different AAVs, but mostly GPA; those observations also indicated the possibility of successful retreatment of relapses. In light of those encouraging results, large-scale RCTs were designed. The pivotal studies assessing rituximab usefulness as a remission-induction agent are the RAVE [24,38] and RITUXVAS trials [39,40]. MAINRITSAN is the reference trial for the maintenance
regimen [41]. Summarized results of the main reported RCTs are reported in Table 1.

42.2.Induction regimens

42.2.1.For GPA and MPA

RAVE was a multicenter, double-blind, non-inferiority trial comparing rituximab (n =

99) to oral cyclophosphamide (n = 98), both combined with CS, to induce remission [38]. All patients had to be ANCA-positive. Patients in relapse (50%) or with a newly diagnosed AAV were included when the disease was considered sufficiently severe to require cyclophosphamide (the reference strategy). That severity was assessed with the BVAS/WG-scoring system, and patients with a score ≥3 were included. Although the study aimed at enrolling patients with severe AAVs, the following exclusion criteria
were applied: pulmonary hemorrhage requiring mechanical ventilation, acute kidney failure with creatininemia >4 mg/dL (350 μmol/L).
Baseline patient characteristics were comparable for the two treatment groups,

with approximately 75% GPA and 25% MPA in each arm. Rituximab (375 mg/m2) was infused weekly for 4 weeks. Control-arm patients received 2 mg/kg/day of oral cyclophosphamide. The primary endpoint at 6 months was the percentage of remissions with BVAS/WG = 0 and CS weaning.
RAVE-trial results demonstrated the non-inferiority of rituximab with 64% of the patients in remission at 6 months compared to 53% of the controls (P<0.001 for the prespecified non-inferiority criterion, non-significant for superiority). For secondary efficacy endpoints, rituximab was more effective than cyclophosphamide at treating relapsing disease (n = 101): 67% vs. 42% remission; no differences were found for the pulmonary and kidney-failure subgroups; and tolerance was deemed comparable for the two groups, even though leukopenia occurred more frequently in the cyclophosphamide arm, while rituximab recipients had more frequent hospitalizations and malignancies. In an extended RAVE–follow-up study, outcomes were assessed 18 months after completing the induction regimen [24]. After achieving complete remission, cyclophosphamide-group patients were prescribed azathioprine (2 mg/kg/day) for 12– 15 months, while rituximab recipients took a placebo until the end of the study period. No between-group differences were observed for sustained-remission or relapse rates and AEs. Rituximab recipients’ remissions were sustained for 64%, 48% and 39% of the patients at 6, 12 and 18 months, respectively. Thus, a single rituximab cycle proved to be non-inferior to cyclophosphamide–azathioprine standard-of-care after 18 months of follow-up (P<0.001). Intriguingly, at 6 and 12—but not 18—months, rituximab appeared to achieve superior remission rates than standard therapy for the subgroup of patients with relapsing AAVs at inclusion [24]. That observation was consistent with the reconstitution of peripheral B cells. In a post-hoc analysis of selected patients with renal involvement, remission, relapse and AE rates were comparable [42]. Published at the same time as RAVE results, RITUXVAS-trial enrollment was restricted to newly diagnosed GPA or MPA with renal involvement, or renal-limited AAV [39]. Patients with renal disease of any severity were recruited, even those on hemodialysis, and median estimated glomerular filtration rate was 18 mL/min/1.73 m2. In that open-label trial, patients were randomly assigned to receive either rituximab plus 2 cyclophosphamide pulses without a maintenance regimen (n = 33) or the standard of care, i.e., 6–10 cyclophosphamide pulses (15 mg/kg) over 3–6 months, relayed by azathioprine (n = 11). Rituximab (375 mg/m2) was infused weekly for 4 weeks. All patients also received CS that were tapered progressively. The primary outcomes were month-12 sustained remission and AE rates. Efficacy was comparable for the classical treatment strategy and rituximab combined with 2 cyclophosphamide pulses, respectively: 82% and 76% remissions. Also, renal function improvement, time to remission and pulmonary manifestations were similar for the two groups. AE rates were the same. The main limitations of that study were the small sizes of the groups, the absence of blinding and the rituximab-arm protocol with concomitant use of cyclophosphamide. Extended follow-up for 24 months after completing induction revealed no between-arm differences for the composite outcome of death, end-stage renal disease and/or flare that occurred in 36%–42% of the participants [40]. Those seminal studies led to rituximab being authorized or licensed as first-line therapy for active severe GPA or MPA and revised the paradigm for standard-of care induction. As early as 2010, rituximab appeared to be a valuable therapeutic alternative to cyclophosphamide. Even though its superiority to cyclophosphamide was not demonstrated in any study, rituximab non-inferiority was clearly established with a similar safety profile. The study results also highlighted the need for maintenance therapy to sustain remissions, because a single rituximab cycle was apparently insufficient to prevent future relapses in the majority of patients [24,43]. Since then, no other RCT evaluating rituximab for AAV-remission induction has been published. Although the serious situations of severe pulmonary hemorrhage and renal insufficiency were not included in the rituximab-based RCTs, the authors of several uncontrolled studies reported using it to treat those manifestations [44–46]. Albeit not controlled and of small size, those studies’ results suggest rituximab may be effective in these patients as well. A small percentage of AAVs do not respond to cyclophosphamide or rituximab- induction regimens. To date, no RCT has addressed this issue to help define the best second-line strategy. However, several studies that combined the two drugs to improve the remission rate and prevent long-term relapses yielded controversial results [44,45]. That approach has been proposed as an alternative for refractory diseases but needs further assessment. 42.2.2.For EGPA EGPA patients were excluded from the RAVE and RITUXVAS trials, and no RCT has evaluated rituximab efficacy against EGPA. So far, evidence of rituximab benefits in these patients has been limited to case series and small-sized, open-label studies on refractory/relapsing EGPA [47–51]. The encouraging preliminary results are being tested in a prospective RCT (REOVAS), comparing rituximab to cyclophosphamide, each combined with CS [18]. 42.3.Maintenance therapies For several decades, it has been known that AAV management should be prolonged after remission-induction with another phase to maintain remissions and prevent relapses. However, once remission was achieved with rituximab, the real need for a maintenance regimen has been explored by withholding treatment until relapse. Below, different therapeutic options are detailed. 42.3.1.The conventional approach Knowing that 40%–60% of AAVs relapse within 5 years after achieving remission, several conventional immunosuppressants have been evaluated to prevent relapses: cyclophosphamide, azathioprine, methotrexate and mycophenolate mofetil. The CYCAZAREM trial [52,53] compared maintenance regimens of oral cyclophosphamide (3 vs. 12 months) followed by azathioprine; its results showed that survival and relapse rates were comparable for the two groups, thereby demonstrating that a “lighter” maintenance regimen was as effective as a more aggressive one. In our prospective, randomized WEGENT trial, comparing azathioprine- versus methotrexate-maintenance therapy for patients whose AAV remissions had been obtained with CS and cyclophosphamide pulses, respective relapse rates were 36% vs. 33%, after a mean 29 months of follow-up [54]. It should be noted that 73% of those relapses occurred after the study drug was discontinued, with 15.1 vs. 13.6 relapses/100 patient-years, respectively. Pertinently, methotrexate is contraindicated in patients with severe renal insufficiency (glomerular filtration rate <30 mL/min). The abilities of azathioprine versus mycophenolate mofetil to prevent AAV relapses were also investigated. According to a prospective randomized study, following cyclophosphamide induction, azathioprine was superior to mycophenolate mofetil, which led the authors to conclude that the latter should not be a first-choice agent to sustain remissions [55]. The extended RAVE–trial follow-up–study results showed that, at 12 and 18 months, respectively, complete remissions were sustained for 48% and 39% of the rituximab– placebo recipients versus 39% and 33% of the cyclophosphamide–azathioprine group [24]. Induction regimens yielded comparable remission rates, highlighting the limited usefulness of azathioprine as maintenance therapy after cyclophosphamide, compared to the rituximab–placebo sequence. However, relapse rates remained very high for both groups, signaling loud and clear that a sufficiently effective maintenance regimen remained elusive, and the need for further studies to explore other therapeutic approaches after rituximab-obtained remission. 42.3.2.Sustaining rituximab-induced remission As shown by MAINRITSAN-trial findings, sustaining remission with low-dose rituximab infusions every 6 months for 18 months seems more reasonable than no intervention at all. In that prospective RCT, azathioprine was compared to 500 mg of rituximab infused every 6 months for 18 months [41], with the first infusion given 3–4 weeks after the end of cyclophosphamide-and-CS remission induction, followed by the second, 2 weeks later, and biannual infusions thereafter. At the end of follow-up, at month-28 post- randomization and 10 months after the last rituximab infusion, 5% of rituximab recipients versus 28% of azathioprine-treated patients had relapsed. As stipulated in the protocol, no further treatment was given after stopping the trial agents. At month 60, despite relapses having occurred in both groups, rituximab remained superior to azathioprine at maintaining remission with a clear between-group difference [23]. Most relapses occurred 18–24 months after the last rituximab infusion. Although MAINRITSAN-trial results clearly demonstrated rituximab superiority over azathioprine; they also clearly signaled that rituximab does not cure AAVs. Pertinently, patients could relapse months or years after stopping it. Those observations raised new questions, such as: Should patients be retreated with rituximab beyond 18 months? Is continuing maintenance therapy with azathioprine of interest? The former question was partially answered by the MAINRITSAN3 trial, which compared, post-randomization, four additional 500-mg rituximab infusions, at 6-month intervals, to placebo, for patients who had previously been given rituximab over 18 months (every 6 months or as needed based on trimestrial laboratory results: ANCA- titer increase or reappearance and/or CD19+ B-cell–reconstitution) [56]. Comparing rituximab versus placebo groups, relapse-free–survival rates at month-56 post- induction were 96% vs. 74.3%, respectively, while severe AE rates were similar. It is expected that the study results will further underscore the indication for prolonged rituximab administration, counterbalanced with the long-term risk of AEs. It seems reasonable that, in the future, prognostic factors and predictors of relapses will be used to adapt treatment duration individually for each patient. Regarding the question about azathioprine usefulness as a maintenance agent, the results of earlier investigations indicated its low impact. RAVE-trial results demonstrated that azathioprine was not superior to placebo to maintain AAV remissions, after comparable remission rates had been obtained with cyclophosphamide or rituximab. The MAINRITSAN-trial results demonstrated rituximab superiority over azathioprine. Taking those findings together [38,41], we think that azathioprine has limited clinical impact on relapse occurrence, even though the authors of a prospective trial [57] claimed that 48 vs. 24 months of azathioprine intake led to fewer relapses. Because azathioprine is now known to be inferior to rituximab at maintaining AAV remissions, any advantage of using azathioprine to sustain remissions seems minor. Moreover, even in the absence of prospective trials, that conclusion can probably also be applied to methotrexate and mycophenolate mofetil. The American College of Rheumatology guidelines presented at the 2019 ACR Congress and the French recommendations [58] recognize rituximab as the first-choice therapy to maintain AAV remissions. The MAINRITSAN-trial therapeutic regimen, based on biannual 500-mg rituximab infusions, was validated by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA). Other therapeutic schedules for AAVs have been evaluated: the RITAZAREM study, presented at the 2019 ACR Congress, compared a 1000-mg rituximab infusion, every 4 months, for a total of five doses, to azathioprine (2 mg/kg/day) for patients whose remissions had been induced by rituximab [59]. Its results at 20 months further highlighted the superiority of rituximab with a relapse rate of 13% vs. 38% for the azathioprine group, with respective more frequent, severe AE rates of 36% vs. 22%, and comparable infection rates. 42.3.3.Predicting relapses Depending on the prospective study, predicting relapses is more-or-less possible and, therefore, so is the usefulness of modulating maintenance treatment. ANCA are sometimes predictors of relapses: relapse rates are lower for patients with anti-MPO ANCA-positivity, while those anti-PR3–positive are at high risk of relapse. Based on our long-term analysis of the MAINRITSAN-trial data, anti-PR3–ANCA presence or absence at diagnosis and persistent PR3-ANCA–positivity 12 months after starting maintenance therapy were associated with more frequent relapses than when ANCA had disappeared at 12 months [23]. ANCA reappearance was also predictive of AAV relapses or flares. Based on one of our prospective trials [60] designed to determine whether ANCA titer increase or reappearance and/or the presence or absence of CD19-expressing B cells could predict relapses, the time of rituximab reinfusion could be adapted to those laboratory findings and, hence, AAV patients in remission could be given less rituximab (3 infusions (i.e., 1500 mg) vs. 5 (2500 mg)). However, the results of that study also showed that ANCA-positivity or -negativity and ANCA titer were not reliable predictors of relapses. 42.4.Rituximab safety in treating AAVs Although overall rituximab safety assessed during RCTs was equivalent to the standard of care, some discrepancies for specific AEs are known. The RAVE-trial analysis, with a predefined combination of the most clinically relevant AEs, highlighted higher overall rates for the cyclophosphamide group (33%) than rituximab recipients (22%, P=0.01) [38]. Rituximab tolerance reported in RCTs and other studies is reviewed below. 42.4.1.Immediate reactions Reaction to rituximab infusion is a well-known AE that may be an allergic process directed against the chimeric antibody (type I hypersensitivity reaction) or secondary to cytokine release after B-cell lysis. It was observed in only five of 229 patients in the RCTs [24,38,39,41] and precluded further rituximab use in one of them. The infusion- reaction frequencies for rituximab and control groups did not differ significantly, notably with systematic prophylaxis and close monitoring. The rates of these reactions were not reported in other studies on AAV patients [61], in contrast to the high rates described for recipients with hematological malignancies, in whom it could be explained by more killed B cells [62]. Also, exacerbation of GPA orbital or ocular involvement was reported in two patients immediately after rituximab infusion [63]. 42.4.2.Systemic infections These events remain a major concern and may be fatal. Six, 12 and 18 months after a single rituximab cycle, respectively, 7%, 18% and 12% of the patients enrolled in RCTs experienced severe infections [24,38,39]. Those rates did not differ from those of patients assigned to receive the standard-of-care regimen. In the MAINRITSAN trial, 19% of rituximab recipients developed severe infections compared to 14% taking azathioprine [41]. In a retrospective study on 192 rituximab-treated AAV patients, 25% of them developed severe infections, mainly of the respiratory tract [64]. Opportunistic Pneumocystis jirovecii pneumonia occurred rarely in rituximab- treated patients participating in RCTs: 3 (1.3%) out of 224 [23,24,38,39,41]. That observation contrasts with other studies that reported it to be a frequent complication [7] and may simply indicate the more systematic use of prophylaxis in RCTs. Notably, after the rituximab-based regimen, other opportunistic infection rates are known to be elevated: varicella-zoster virus, cytomegalovirus reactivation. Some concerns have been raised regarding rare cases of JC-virus progressive multifocal leukoencephalopathy but rituximab implication remains uncertain [65]. However, the results of the abovementioned RCTs and subsequent studies did not show the frequencies of those infections to be alarming. 42.4.3.Hypogammaglobulinemia Although hypogammaglobulinemia was not observed in RCT participants, moderate-to- major episodes were associated with retrospective rituximab-treated AAV cohorts [66,67]. Diminished IgM was more frequent than IgG. Hypogammaglobulinemia severity seemed to be more severe for patients with low serum IgG levels at rituximab onset but also for those requiring retreatment and after cyclophosphamide use during the preceding months [66–68]. In an observational study on 160 AAV patients, half of them did not have sustained IgG nadirs, even under prolonged rituximab use [66]. The duration of hypogammaglobulinemia varied widely from one patient to another and no reliable factors able to predict normal immunoglobulin-level recovery have yet been identified. The potential relationship between the extent of IgG decline and the risk of infection for rituximab-treated patients with autoimmune diseases was not clearly established in two studies that had enrolled more than 200 AAV patients [66,67]. However, a study on 700 patients with autoimmune diseases, mainly rheumatoid arthritis, treated with rituximab demonstrated that low IgG levels at rituximab onset and after its administration were predictive of serious infectious events [69]. 42.4.4.Malignancies Although the frequencies of cancers did not differ between RCT groups treated with rituximab or cyclophosphamide [24,38–41], induction-regimen analysis revealed a higher percentage of malignancies in rituximab-arm patients. The short follow-up of those studies limits our ability to interpret that information. For a cohort of 323 AAV patients, followed for a mean of 5.6 years, the cancer risk was similar for rituximab recipients and the general population, whereas those given cyclophosphamide had a 4.6- fold higher risk of malignancy than rituximab-treated patients [70]. AAV patients’ increased short- and long-term cancer risks have mainly been associated with high exposure to cyclophosphamide, which is known to be responsible for increased frequencies of leukemia, bladder and non-melanoma–skin cancers [71,72]. Prolonged azathioprine exposure is also associated with a higher risk of developing skin cancers [73]. Rituximab was not associated with such risk in AAV patients [70] or those with lymphomas based on >15 years of experience [74]. Even though additional studies on long-term follow-up of AAV patients are warranted, rituximab appears to be a valid therapeutic alternative of choice for patients at high risk of cancer, like those with cumulative cyclophosphamide or azathioprine exposure.

42.4.5.Other AEs

Other AEs reported for rituximab-treated patients with AAVs or other autoimmune diseases are prolonged, late-onset neutropenia and thrombopenia. Those AEs were seldomly described in AAV recipients. Granulocyte colony-stimulating factor is an option for treating late-onset neutropenia but its real usefulness remains to be ascertained
[75]. The risk of recurrence after rituximab rechallenge appears to be low [75].

Unlike cyclophosphamide, rituximab has not been associated with fertility or teratogenic concerns, although data are scarce. Those observations make rituximab a better option for women of childbearing age. Nonetheless, rituximab administration is not encouraged during pregnancy or breastfeeding, as it can be transmitted to the fetus/baby and potentially induce immune suppression, especially during the later stages of pregnancy. Moreover, because rituximab can persist in the blood for months after the last infusion, it can still be a threat for a fetus when infused prior to conception. Therefore, rituximab is usually discouraged during pregnancy and effective contraception is obligatory for woman of childbearing age until 12 months after the last infusion. To date, five women with severe AAVs have been treated with rituximab before or during pregnancy: no safety concerns were reported [76]. Among 19 rheumatoid arthritis patients who received rituximab prior to [77] or during [78] pregnancy, none

experienced more frequent adverse outcomes, such as miscarriages. No congenital malformation attributed to rituximab has ever been reported in humans or animals. Despite the limited safety data available, rituximab may be considered a therapeutic alternative during pregnancy in exceptional circumstances.

3.Practical considerations


The administration protocol for the remission-induction regimen, approved by the FDA and EMA, is 375 mg of rituximab/m2 on days 0, 7, 14 and 21, based on the results of the pivotal RAVE and RITUXVAS RCTs [38,39]. However, according to small retrospective studies, the protocol for rheumatoid arthritis patients (1 g × 2, 2 weeks apart) might be as effective [79,80] but that possible equivalence will have to be further evaluated in other studies. Rituximab is usually administered with slowly increased flow rates: the first infusion commonly lasts 4–6 hours, with shorter durations for the subsequent administrations in the absence of an allergic reaction.
Once induction has achieved remission, when to start remission-maintenance therapy with rituximab must be considered in light of the initial regimen. Patients who had previously received cyclophosphamide for induction should receive the first remission-maintenance infusion of rituximab within 4 weeks of completing the former regimen, as in the MAINRITSAN trial [41]. For patients who had previously received rituximab for induction, reinfusion can be considered at month 6 after the end of the initial regimen, like many patients in the MAINRITSAN2 trial [56]. Additional maintenance infusions are then administered every 6 months. The FDA and EMA

approved the following maintenance regimen in November 2018: 500 mg on days 0 and 14, then every 6 months for at least 18 months. After post-hoc analysis of MAINRITSAN2 data, the scheduled day-14 infusion, as specified in the trial protocol, no longer seems necessary [81].

3.2.How long should rituximab administration last?

AAV-remission–maintenance therapy with rituximab has been approved by the FDA and EMA, according to the effective MAINRITSAN-trial schedule: 500 mg every 6 months for 18 months. Recent MAINRITSAN3 results indicate that rituximab retreatment until 46 months has a good efficacy/safety ratio [56]. In the RITAZAREM study [59,82], 1000-mg of rituximab were infused every 4 months until month 20. Thus, the optimal administration duration, dose and interval for maintenance therapy requires further refinement.

3.3.Place of biological marker monitoring

The evolutions of various biological markers during rituximab use and their performances as prognostic tools to guide the treatment strategy have been examined in numerous investigations. The most studied markers are CD19+ B-cell counts and ANCA titers and/or reappearance.
The peripheral B-cell counts (usually assessed as CD19+) of almost 95% of AAV patients were depleted within 1 month of starting rituximab. However, the definition of B-cell depletion ranges among studies from 0/mm3 to <20/mm3. But it should be noted that the lack of depletion does not always mean treatment failure: in the RAVE trial, several patients entered remission without having B-cell depletion [38]. Notably, according to several studies, some patients relapsed almost exclusively after B-cell repopulation [24,40,83]. That finding was not confirmed by other authors, who evaluated induction or maintenance regimens: some patients relapsed even in the absence of detectable B cells [41,79,84]. Therefore, B-cell monitoring alone is not a reliable indicator of remission or relapse risk. ANCA-monitoring results have also been discrepant or inconsistent. Rituximab- treated ANCA-positive GPA patients participating in the RAVE trial were more likely to become ANCA-negative than those given cyclophosphamide, but this difference was not associated with a better clinical outcome [38]. Notably, PR3-ANCA–titer increase was associated with a risk of subsequent, notably severe, relapse only for rituximab-treated patients [85]. The authors of another study suggested that rising ANCA titers predicted relapse [83]. In contrast, the extended follow-up of RITUXVAS participants showed that only one-third of the patients with increased ANCA titers relapsed [40]. MAINRITSAN2- trial results indicated that monitoring B-cell counts, ANCA evolution or a combination of both provided no prognostic value for the risk of relapse [60]. Exploratory studies derived from the RAVE trial investigated the potential for clinical impact of novel biological marker levels: circulating CD5-positve B-cell counts [86] or granulocyte granularity index at inclusion [87]. Although those studies yielded some interesting findings, their contribution to clinical practice remains to be confirmed. Finally, serum rituximab levels were not associated with any meaningful clinical outcomes and, thus, determining them does not appear to be a useful tool to guide retreatment [88]. 3.4.Anti-infection prophylaxis Several steps can be taken to limit, if not prevent, some infections. It is strongly recommended that AAV patients, like other immunocompromised individuals, should be vaccinated against influenza and pneumococcal infections [89]. Given that vaccine immunogenicity has been demonstrated to be diminished after B-cell depletion in patients with autoimmune disorders, vaccines should be administered and, whenever possible, before rituximab is started [90,91]. The standard regimen for anti- pneumococcal immunization combines pneumococcal conjugate vaccine (PCV)-13 injection and pneumococcal polysaccharide vaccine-23 injection 2 months later. An ongoing trial is evaluating the immunogenicity and safety of two reinforced, innovative PCV regimens in rituximab-treated AAV patients [92]. Pertinently, live vaccines are contraindicated for patients being treated with rituximab, at least until 6 months after the last infusion. Among patients with persistent hypogammaglobulinemia, fewer than 5% of the patients received immunoglobulin-replacement therapy to prevent infections [66,67]. As previously detailed, low IgG level at RTX onset and IgG decline after rituximab were associated to increased infection rates [67,69], although no clear threshold was established to guide initiation of immunoglobulin replacement therapy [66,67]. Therefore, immunoglobulin-replacement therapy should be reserved for patients with recurrent symptomatic bacterial infections. To better determine the modalities of this supportive therapy, e.g., the intervention threshold and the serum IgG level to target, additional investigations are needed [93]. Adapted prophylaxis, with co–trimoxazole or pentamidine aerosolizations, is recommended to prevent Pneumocystis jirovecii pneumonia, [64,94]. It should be mentioned that, according to a retrospective study on rituximab-treated AAV patients, co–trimoxazole also limited the risk of severe bacterial infections [64]. Moreover, co– trimoxazole use by GPA patients was reportedly associated with fewer relapses [95]. It has been thoroughly demonstrated that adding rituximab to polychemotherapy increased the risk of hepatitis B virus (HBV) reactivation for lymphoma patients with resolved HBV infection (HBsAg–, HBcAb+) [96,97]. It is now acknowledged that these patients should receive antiviral prophylaxis [97,98]. Information on HBV reactivation in rituximab-treated patients with autoimmune diseases is scarce [99]; indeed, some AAV patients experienced reactivation but the real frequency is unknown. Therefore, preventive antiviral therapy remains controversial but, if not used, all patients should undergo repeated HBV-DNA monitoring [100,101]. Pertinently, all patients should be screened for HBV infection prior to starting rituximab. Herpesvirus infections (herpes simplex, varicella-zoster virus, cytomegalovirus) are more frequent after administration of biological agents. However, too few data are available for rituximab-treated AAVs to draw any conclusions about the prophylactic use of antivirals or available anti–varicella-zoster vaccine. 4. Conclusion It has been clearly demonstrated that rituximab is non-inferior to cyclophosphamide to obtain remissions of the most severe forms of MPA and GPA. To date, no reliable data are available for EGPA. In addition, rituximab superiority to azathioprine to sustain those remissions has been established but long-term remission management with this biotherapy requires further evaluations 5Expert opinion We unreservedly think that rituximab has revolutionized AAV therapy. Although trials were conducted on patients almost exclusively ANCA-positive, it is our opinion that the results can be extended to ANCA-negative AAV patients. Rituximab is a good alternative to cyclophosphamide to induce remissions of severe MPA or GPA. Because CYC and rituximab have comparable efficacies, clinicians can choose between the two for induction of remission. In our opinion, rituximab should be preferred because of its more favorable risk/benefit ratio. Rituximab might even be more beneficial for a relapse and after cyclophosphamide failure. Its safety profile makes it the better choice in situations in which cyclophosphamide is likely to be problematic: women of childbearing age, high cumulative cyclophosphamide dose (i.e., >20 g), patients with malignancies. Although we now prefer rituximab for most patients, we still consider cyclophosphamide a first-choice molecule for patients who have not been evaluated in prospective trials and with clinical characteristics against which cyclophosphamide has proven to be effective. Indeed, we think data are still insufficient to recommend rituximab for patients with severe pulmonary hemorrhage requiring mechanical ventilation or acute renal insufficiency (creatininemia >350 μmol/L).
Future research studies should address rituximab administration in all those contexts, as well as using rituximab to treat non-severe AAVs, since many patients with non-severe disease suffer several relapses and develop CS-related complications. The place of rituximab and its potential benefits in treating EGPA will hopefully be clarified by the results of the ongoing REOVAS trial. Based on previous reports and EGPA pathophysiology, rituximab should be beneficial against its systemic vasculitis manifestations but will probably have a limited impact on the predominantly eosinophilic manifestations, like asthma and chronic rhinosinusitis.
Some physicians in the vasculitis-management community choose not to prescribe

maintenance therapy once remission has been obtained, preferring to wait for an overt

relapse to do so. Because the severity of a new attack and its possible sequelae

(impaired renal function, for example) cannot be anticipated, we do not recommend that watch-and-wait approach. We strongly recommend a relapse-prevention strategy with remission-maintenance therapy for MPA and GPA, for which rituximab is the drug of choice when an immunosuppressant is needed, depending on initial disease severity. Even though this biological agent does not cure AAVs, it is by far the most effective therapy to date with an acceptable safety profile. Currently, we recommend maintaining remission with rituximab, 500-mg infusion at fixed 6-month intervals until 18 months. Should that strategy fail, maintenance infusion intervals can be shortened to 4 months and the dose of each infusion increased to 1000 mg. Such a strategy should only be considered for second-line treatment.
For patients whose disease does not respond (refractory) to cyclophosphamide or rituximab, we usually switch drugs, which is most often successful. We prefer this strategy to systematically combining rituximab and cyclophosphamide, as proposed in the RITUXVAS trial. For patients who relapse after initial cyclophosphamide use, we switch to rituximab, to which most respond. When relapse occurs several months after an initial positive response with rituximab, rituximab is again administered, usually with another positive response.
Results from recent trials addressing rituximab use beyond month 18 of remission indicate that retreatment with rituximab beyond 4 years still has a good efficacy/safety profile. According to our experience, extended biannual retreatment beyond 4 years could be considered for patients at higher risk of relapse: patients with previous relapse(s) and those with persistent PR3-ANCA–positivity. Optimal immunosuppressive therapy duration is an important aspect of treating AAVs in light of their frequent and potentially debilitating relapses. But a good equilibrium must be

sought with the risks of AEs, particularly infections. In that context, we must still endeavor to better assess and define strategies, combining vaccination, prophylaxis and prediction of symptomatic prolonged hypogammaglobulinemia, to limit the rituximab- related risk of infection. We found that infections did not occur in most patients with
low IgM levels whose hypogammaglobulinemia can persist for years without developing an infection. A low IgG level is rarer and can be associated with severe infections. In that setting, after the first infection, we recommend immunoglobulin-replacement therapy,
in accordance with the management guidelines for humoral immune deficiency. Even in that context, rituximab indications remain the same and treatment should be pursued.
Another important avenue of research concerning rituximab use is to characterize routinely available biological markers to help guide treatment monitoring. To date no individual marker has been repeatedly proven useful. According to MAINRITSAN2-trial findings, combining ANCA testing and circulating B-cell levels could orient rituximab retreatment. This very promising strategy would limit rituximab infusions, achieving efficacy similar to systematic retreatment, with potentially lower exposure and fewer AEs. Those observations need to be confirmed. Because AAV pathophysiology is complex and heterogeneous from one patient to another, it is likely rituximab will be more beneficial for some than others. Identifying prognostic markers that assess B-cell involvement and predict rituximab efficacy are needed. Another therapeutic option would be to use other B-cell–depleting strategies already applied to hematological malignancies and rheumatoid arthritis. Other anti-CD20 antibodies are available and may be useful: (1) fully humanized (i.e., ofatumumab), to avoid allergy to rituximab; or (2) more effective than rituximab at inducing cell death (i.e., obinituzumab).
Along the same line of thinking, it can be hypothesized that, in the future, several

targeted biological therapies will be used concomitantly because some of them may target complementary pathogenic mechanisms, generating synergistic efficacy. Potential regimens include combining anti–B- and anti–T-cell therapies for MPA and GPA, or anti– B-cell and anti–interleukin-5 for EGPA. Moreover, personalized, patient-centered medicine is one of the major challenges of AAV management.



This paper was not funded.

Declaration of interests

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer Disclosures
Peer reviewers on this manuscript have no relevant financial relationships or otherwise to disclose.

List of abbreviations

ANCA: anti-neutrophil cytoplasmic antibody AAV: ANCA-associated vasculitis
CS: corticosteroids

EGPA: eosinophilic granulomatosis with polyangiitis FVSG: French Vasculitis Study Group
GPA: granulomatosis with polyangiitis

MAINRITSAN: randomized–controlled trials evaluating MAINtenance of Remission using RITuximab in Systemic ANCA-associated Vasculitis
MPA: microscopic polyangiitis

RAVE: Rituximab in ANCA-Associated Vasculitis trial

RITAZAREM: randomized–controlled open trial comparing RITuximab to AZAthioprine as an extended REMission regimen
RITUXVAS: randomized trial of RITUXimab versus cyclophosphamide to induce

remissions of in ANCA-associated VASculitides



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\Table 1. Main randomized–controlled trials evaluating rituximab for ANCA-associated vasculitides.

Study [ref]
Compared regimens*
N† subjects
Patients & inclusion criteria
Rituximab regimen‡
Main results

Remission-induction phase

RAVE [38]
RTX vs. oral CYC efficacies (non- inferiority evaluation)
99 vs. 98
Relapsing or newly diagnosed ANCA+ GPA (75%) or MPA (25%)
4×375 mg/m2/wk
At M6, RTX was non-inferior to CYC with comparable

Exclusion of severe safety profile pulmonary
hemorrhage and creatininemia >350 μmol/L
RITUXVAS RTX (+ 2 CYC 33 vs. Newly diagnosed 4×375 At M12, similar
[39] pulses) vs. 11 ANCA+ AAVs with mg/m2/wk, efficacy and
standard IV CYC renal involvement: combined safety of the
(superiority GPA (50%), MPA with 2 CYC RTX-based
evaluation) (36%) and RLV pulses regimen vs. the
(14%) standard CYC regimen
Remission-maintenance phase
RAVE Long-term efficacies 99 vs. RAVE study patients No RTX At M18, RTX was
extension [24] of a single RTX 98 reinfusion non-inferior to
cycle for after sequential CYC–
remission- induction AZA to sustain
induction vs. CYC, protocol: remissions but
followed by AZA placebo from relapses were
M6 frequent
MAINRITSAN RTX vs. AZA for 57 vs. Complete remission 500 mg×2 at At M28, RTX
[41] remission- 58 after induction (IV M6 after efficacy was
maintenance CYC–CS regimen) starting superior to AZA
(superiority for included induction; to maintain
evaluation) patients with then 500 mg remission, with
relapsing or newly every 6 comparable
diagnosed ANCA+ months until safety profiles
GPA (76%), MPA M24 (20%) and RLV

MAINRITSAN2 Two RTX-based 81 vs. AAVs (>90% ANCA+) Either the Relapse rates did
[60] regimens: fixed 81 with newly MAINRITSA not differ
biannual vs. diagnosed (64%) or N fixed RTX significantly
individually tailored relapsing (36%) schedule between the 2
lab-based (CD19 disease before or groups, with 3
and ANCA) induction (CYC or 500 mg of RTX (vs. 5) infusions
reinfusions RTX): GPA (72%), at M6 and in the tailored arm

MPA (28%)
then only according to lab B-cell counts and/or ANCA titers

RTX continuation vs. placebo after obtaining complete
50 vs. 47
MAINRITSAN2 patients still in remission at M28:
RTX reinfusions (500 mg) at
Relapse-free survival was superior for RTX-

remission following MAINRITSAN2
GPA (70%) and MPA (30%); 50% ANCA+ at inclusion
M28, M34, M40 & M46
treated patients, with comparable AEs

RTX continuation vs. AZA after
obtaining complete remission with
85 vs. 85
Relapsing anti-PR3 (72%) or anti-MPO (28%) ANCA+ AAVs
RTX (1 g) at M4, M8, M12, M16 &
RTX was superior to AZA at preventing relapses with fewer severe AEs

AAV, ANCA-associated vasculitis; AZA, azathioprine; AEs, adverse events; CS, corticosteroids; CYC, cyclophosphamide; GPA, granulomatous with polyangiitis; IV, intravenous; M, month; MPA, microscopic polyangiitis; MPO, myeloperoxidase; PR3, proteinase-3; RLV: renal-limited vasculitis; RTX, rituximab; wk, week.
*Because CS were always part of the therapeutic regimens and were used similarly for both arms, they are not systematically reported in the table.
†N, the first number indicates the RTX-treated group vs. the other arm.
‡For treatment chronology, month (M) numbers start with induction-therapy onset, i.e., M6 designates 6 months after starting induction.