Maintenance with Rituximab in anti-neutrophil cytoplasm antibody-associated vasculitis

Introduction

Anti-neutrophil cytoplasmic antibody associated (ANCA) vasculitis is characterized by infiltration of neutrophils into small blood vessel walls, resulting in autoinflammation and necrosis^[1]. Microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), eosinophilic granulomatosis with polyangiitis (EGPA), and renal-limited ANCA-associated vasculitis are considered the main ANCA associated vasculitides (AAV). Granulomatosis with polyangiitis and MPA present similarly and have significant disease overlap, therefore, they are often considered together in terms of management. Eosinophilic GPA is a process defined by eosinophilic pneumonia and its manifestations are dictated by eosinophilic inflammation; treatment strategies for this disease are therefore focused on this distinct aspect of its pathogenesis and differ from the treatment of the other ANCA associated vasculitides.

These rare diseases mostly affect individuals over the age of 50 and can progress to life threatening, fulminant multisystem disease with complications such as diffuse alveolar hemorrhage (DAH) and necrotizing glomerulonephritis causing respiratory failure and renal failure, leading to significant mortality rates^[2]. Furthermore, despite significant treatment advances in remission induction, preventing disease relapse and successfully maintaining disease remission continues to provide a significant challenge to physicians. Anti-neutrophil cytoplasmic antibody associated vasculitides therefore must be viewed as chronic diseases with complex treatment strategies that require long term immunosuppression.

Given the rarity of these diseases and the complexity of their treatment, significant efforts have been made over the years to investigate safe, effective induction and maintenance therapies for these patients. Prior to these significant advancements, AAV ran a fulminant and fatal course with rapidly progressive multisystem disease and an extremely high mortality rate. Eighty-two percent of patients with untreated GPA would die in 1 year and 90% would die in 2 years^[3]. Initially, induction therapy with glucocorticoids was attempted and improved survival rates to 1 year, however, this strategy was associated with a multitude of side effects and a high rate of disease relapse^[4].

In the early 1970s and 1980s, promising evidence of cyclophosphamide (CYC) use in conjunction with glucocorticoids for induction therapy surfaced. A paramount study in 1985 revealed that 93% of patients with GPA followed over a 21-year period who received induction therapy with CYC and glucocorticoids achieved disease remission^[3]. Unfortunately, however, the cytotoxic side effects of long-term CYC use became apparent including leukopenia, hemorrhagic cystitis, infertility and 31-fold increased risk of bladder cancer^[4]. Despite being an effective agent in inducing disease remission in AAV, the cytotoxicity of CYC provided long term harm to patients and thus, was not an ideal agent for maintaining disease remission. Further research was needed to discover new treatment modalities that would deliver less harmful side effects.

Multiple studies explored alternate induction therapies for AAV, most notably the CYCLOPS trial in 2009 (comparing IV pulse doses of CYC vs. daily oral CYC and prednisolone as induction therapy)^[5], the MORAM trial (exploring efficacy of methotrexate (MTX) in inducing remission vs. CYC and prednisolone)^[6], and the MEPEX and PEXIVAS trials which studied the use of plasma exchange vs. glucocorticoid therapy for patients with AAV and sought to determine whether plasma exchange resulted in any significant difference in renal recovery, progression to ESRD or, overall incidence of death in patients with ANCA associated vasculitis^[7,8]. Although promising, these alternate therapies did not prove to be any more efficacious than CYC while still having high relapse rates and significant drug toxicities.

Two randomized controlled trials exploring induction therapy with RTX vs. CYC (RAVE and RITUXVAS trials) found that induction therapy with RTX (administered alone in the RAVE trial and co-administered with CYC in the RITUXVAS trial) was non-inferior to CYC alone in inducing disease remission and that RTX did not have an increased risk of adverse events as compared to CYC. Additionally, at month 18 in the RAVE trial and at month 12 in the RITUXVAS trial, RTX alone was shown to be as efficacious in preventing disease relapse as CYC followed by azathioprine (AZA) maintenance therapy^[9,10]. The RAVE trial also found that RTX had a better safety profile than CYC^[9]. This was a cornerstone discovery in that, an induction therapy as effective as CYC (especially in severe relapsing disease) had yet to be discovered with the added benefit that RTX had a better safety profile. Despite these promising discoveries for induction therapy, maintenance of AAV remission still poses a significant challenge to physicians. This has prompted further research into alternative maintenance therapies.

Rituximab in ANCA associated vasculitis

Rituximab is a monoclonal antibody consisting of both human and murine components that specifically targets the B cell CD20 antigen, thus causing removal of B cells from the peripheral circulation^[14]. This is important because B cells have been implicated in the pathogenesis of AAV via their production of ANCAs, activation of the alternative complement pathway, and initiation of inflammatory cascades that induce severe necrotizing vascular inflammation. The ANCA autoimmune response is driven by inhibited suppression of T cells and B cells, and by release of B-cell stimulating factors by activated neutrophils which act to slow the apoptosis of B cells, thus enhancing their proliferation^[15]. Due to the fact that the pathogenesis of AAV is rooted in B cell mediated autoimmunity, it stands to reason that RTX would be of significant therapeutic benefit given its ability to target autoreactive B cells and deplete them from the circulation. As such, RTX provides a promising treatment option for induction and maintenance therapy in AAV because it targets the direct pathogenesis of the disease.

Maintenance therapy with Rituximab in AAV

With the advent of promising research demonstrating RTX as a safe and effective induction therapy, investigators set their sights on this drug as a possible maintenance therapy for patients with AAV. Rituximab showed promise as a maintenance therapy for AAV in early case reports and retrospective reviews. In 2001, the use of RTX was described in a man with a history of chronic, relapsing GPA who did not tolerate treatment of disease relapse with CYC due to bone marrow toxicity, which caused significant anemia. Additional immunosuppressive treatments such as AZA and mycophenolate mofetil (MMF) were attempted, however, the patient did not respond to these treatments and had continued relapses with worsening renal failure and a meningeal flare of GPA. The decision was made to initiate therapy with RTX on a compassionate basis given the patient had been refractory to all conventional treatments and MTX was contraindicated. Subsequently, the patient received 4 infusions of 375 mg/m² of RTX and high dose glucocorticoids. The patient entered complete remission after treatment with RTX and it was observed that his cytoplasmic ANCA (cANCA) and B lymphocyte levels had completely disappeared. At 11 months after treatment, the patient’s cANCA and B lymphocytes reappeared, yet he did not have any signs or symptoms of disease relapse; he was preemptively treated with RTX at that time and remained in complete remission at 18-month follow up^[16][Table 1].

In 2005, a case series reviewed 9 patients with a history of GPA or MPA who had either been resistant to treatment with CYC or, had experienced recurrent relapses after cessation of CYC therapy. Two of the patients were myeloperoxidase (MPO) - ANCA positive and 7 were proteinase-3 (PR-3) ANCA positive. These patients were treated with RTX infusions in addition to conventional immunosuppressants (AZA, MMF, or a short course of CYC) in order to prevent the formation of antibodies to RTX. Three patients were treated twice with a once per week infusion and four patients were treated four times with a once per week infusion. Eight out of the 9 patients in the study exhibited a complete response to RTX therapy with one patient having a partial response. Responses included improvement of chest x-ray (four patients), cessation of lower extremity gangrene (one patient), improvement of peripheral neuropathy (one patient), remission of renal vasculitis (two patients), and improvement in severe musculoskeletal pain (one patient)^[17][Table 1].

A retrospective study of 8 patients with a history of relapsing or refractory GPA who received RTX infusions in conjunction with ongoing immunosuppressive therapy was conducted in 2007. This study investigated the efficacy of RTX in patients with GPA who had either failed treatment with prior immunosuppressive therapy or, had continued to relapse despite treatment. The study found that RTX infusions improved the clinical outcomes of patients with relapsing or refractory GPA when used in conjunction with other immunosuppressants. Additionally, it was found that the granulomatous manifestations of GPA took longer to respond to RTX therapy (several months) as opposed to the vasculitis manifestations of GPA, which responded within weeks to months^[18][Table 1].

A retrospective data collection two years later in 2009 (the largest data review to be conducted at that time) gathered data from 65 patients across 4 centers in the UK with a history of refractory AAV who received induction therapy with RTX. The study aimed to investigate the efficacy and safety of RTX in patients with refractory AAV as an induction therapy. Complete remission occurred in 49/65 patients (75%), with partial remission occurring in 15/65 patients (23%). Only one patient did not respond to therapy. Furthermore, patients who received preemptive retreatment with 1 g of RTX every 6 months despite not having any symptoms of disease relapse had zero relapses at 11-month follow up, suggesting that RTX was also an effective maintenance therapy in patients with refractory AAV^[19][Table 1].

A year later in 2010, another retrospective review studied RTX as a maintenance therapy in 39 patients with AAV who had already achieved either complete or partial remission. This study aimed to address the direct role of continuous infusions of RTX as a maintenance therapy in AAV patients. All 39 patients followed up after 1 year and 20 patients followed up after 2 years. The results showed that RTX treatment resulted in good disease control throughout the study. Median disease activity was measured according to the Birmingham Vasculitis Activity Score (BVAS), a comprehensive scoring system of all organ systems possibly affected by vasculitis that contains 59 items divided into 9 groups (i.e., general, cutaneous, mucous, renal, etc.). A lower score indicates lower disease activity, versus a higher score which indicates higher disease activity. Median disease activity of the patients in the study was 1 at baseline and improved to 0 at 12 and 24-month follow up. Eighty-seven percent of patients were on cytotoxic immunosuppression at the start of the study vs. 41% at 12-month follow up and 30% at 24-month follow-up^[20][Table 1].

A single center historical cohort study in 2012 observed 53 patients with chronic relapsing GPA over 10-year period from January 1, 2000 to May 31, 2010 in whom RTX was used to maintain remission or, to treat disease relapses. The patients in the study received at least 2 courses of RTX (median number of courses of RTX was 4), with 52 of these patients being PR-3 ANCA positive. All patients who were treated for relapses achieved disease remission. Of the 53 patients, all achieved B cell depletion after induction therapy with RTX. Thirty two out of the 53 patients relapsed and, in all cases, relapses were associated with a rise in PR-3 ANCA levels and the reappearance of CD19+ B lymphocytes in the circulation. Remission was maintained successfully in all patients who were treated with preemptive courses of RTX based on re appearance of B lymphocytes and increases in PR-3 ANCA titers. Overall, this study conveyed the effectiveness of RTX as both an induction and maintenance strategy in patients with AAV^[21][Table 1].

A retrospective study in 2012 examined the outcomes of 28 patients with AAV (4 with MPA and 24 with GPA) treated with RTX for maintenance therapy from 2003-2010. All patients in the study had entered remission with the use of conventional immunosuppressant therapy or RTX and were monitored for relapse rates and tolerance after greater than or equal to 2 RTX infusions used as maintenance therapy. The median range of RTX infusions was 4 with a median follow up time of 38 months from diagnosis or last flare. Out of 28 patients, 2 had pulmonary relapses, 1 patient suffered alveolar hemorrhage 6 months after a RTX infusion and 1 patient developed new lung nodules 11 months after a RTX infusion (this patient was then started on a new induction regimen with RTX which achieved disease remission and was followed by successful RTX maintenance). At final evaluation, 6 patients were in complete remission, 11 patients were in complete remission with irreversible damage and, 9 patients were in partial remission. 7 of these patients had persistent ENT involvement and 2 patients had persistent lung nodules. None of these patients had infusion reactions, 15 patients had hypogammaglobulinemia and 3 patients developed infections. The data of this study suggest that RTX could be used as a safe, effective maintenance therapy in AAV^[22][Table 1]. Since the safety and efficacy of RTX as a maintenance therapy had been established in this study, the next question posed was the efficacy and safety of RTX as compared to other conventional maintenance therapies like AZA. This laid the framework for the largest randomized controlled trial to compare RTX to AZA as maintenance therapy in AAV titled the Maintenance of Remission using Rituximab in Systemic ANCA-associated Vasculitis (MAINRITSAN) trial.

In 2014, the MAINRITSAN trial investigated the use of RTX vs. AZA as a maintenance therapy in patients with AAV. The study was a non-blinded, randomized controlled trial that studied patients with GPA, MPA or renal-limited AAV who had received induction therapy with CYC and glucocorticoids and achieved disease remission. These patients were randomized to receive RTX infusions vs. daily AZA for maintenance therapy and were monitored for disease relapse. After 28 months, 5% of the patients in the RTX group had suffered disease relapses vs. 29% of the patients in the AZA group. Additionally, adverse event rates were similar between the two groups. This study demonstrated that patients in the RTX group had significantly less relapses and an equal number of adverse events as the AZA group, thus conveying the superiority of RTX to AZA in maintaining disease remission in AAV while maintaining a similar safety profile to AZA^[23][Table 1]. One interesting point is that the study was comprised mostly of patients who were anti PR-3 ANCA positive; patients who were anti MPO-ANCA positive and patients who had renal associated AAV comprised a smaller patient population in the study. An interesting point of further investigation would be to do additional trials exploring RTX as remission maintenance in patients who have anti MPO ANCA-positive vasculitis to further determine their responsiveness to RTX treatment.

Adverse effects of Rituximab

Hypogammaglobulinemia has been observed in patients receiving maintenance therapy with RTX, which is of particular concern given the increased risk of developing serious infections when immunoglobulins are low^[23,24]. Literature detailing an ideal threshold immunoglobulin level at which to stop RTX in order to prevent development of serious, life threatening infections has not been described. It has been described that antibiotic prophylaxis is effective in preventing infections in patients who develop hypogammaglobulinemia after RTX therapy. These patients should receive influenza and pneumococcal vaccinations prior to the initiation of treatment in order to prevent infections^[34].

Late onset neutropenia has been described in patients with rheumatic diseases who have received RTX therapy, albeit this is a rare side effect. Several mechanisms have been proposed which could potentially contribute to late onset neutropenia in patients with rheumatic diseases receiving RTX including increased production of B lymphocytes which halts production of T cells and, infiltration of bone marrow and peripheral blood by T-large granular lymphocytes^[34,35].

Progressive multifocal leukoencephalopathy (PML) has also been described in patients with GPA and MPA receiving RTX treatment. A cumulative analysis conducted in 2018 which studied patients receiving RTX for GPA or MPA between 2009 and 2015 showed that the confirmed number of cases of reported PML was very low (< 1 case per 10,000), indicating that this is a rather rare adverse effect of the medication. Despite its rarity, physicians should still be aware of the risk of development of PML in AAV patients receiving treatment with RTX, as these patients have often previously received cytotoxic immunosuppressants which are also known risk factors for development of PML^[36].

Continued use of RTX increases the risk of serious infections depending upon the indication for its use and, the dose at which it is being administered. With regard to AAV patients, a retrospective case review demonstrated that severe infections occurred most commonly within the first year of receiving RTX treatment. Old age and lack of ENT involvement was a risk factor for developing severe infection^[37]. Another study found that bronchiectasis and endobronchial involvement were notable risk factors for development of severe respiratory infections, and that antibiotic prophylaxis with Trimethoprim-sulfamethoxazole was effective in preventing infections in patients with AAV who were receiving RTX infusions^[38].

Efficacy of Rituximab in treating proteinase 3-ANCA vs. myeloperoxidase-ANCA

During the RAVE trial, patient responses to RTX vs. CYC were analyzed based on ANCA-type (PR-3 vs. MPO). The data concluded that RTX was also superior to CYC in maintaining remission specifically in ANCA PR-3 positive patients vs. patients who were positive for ANCA-MPO^[9]. The MAINRITSAN trial enrolled more patients who were positive for anti-PR-3 ANCA in the study than patients who were positive for anti-MPO ANCA, so the results were more indicative of the response of the anti-PR3 ANCA patient population to RTX [Table 1]. Earlier trials also enrolled greater numbers of PR-3 ANCA positive patients^[17,21]. This poses an interesting question as to whether RTX is more effective in treating and preventing disease relapse in patients who are specifically PR-3-ANCA positive and, would be a good subject of future research.

Risk factors for disease relapse in ANCA associated vasculitis

The utility of monitoring the presence of autoreactive ANCA antibodies, ANCA titers and, presence of circulating CD19+B cells as a risk factor for disease relapse in AAV has been a matter of debate due to conflicting data on this subject throughout the years. It is particularly useful to know this information as prevention of relapses is paramount in reducing organ damage and increasing survival in AAV patients. There is conflicting evidence regarding this subject because while ANCA titers do often drastically decrease in patients who have received induction therapy, some patients who have achieved disease remission can remain ANCA positive and certain patients who are negative for ANCA autoantibodies can still relapse. The same question is posed regarding the presence of circulating CD19+ B cells as relapses have occurred regardless of the presence of B cells in AAV patients. The MAINRITSAN 2 trial addresses this fact as the study notes that four patients experienced disease relapses despite being ANCA negative and having no B cells in the circulation.

A single center cohort study conducted in June 2020 sought to investigate the role of the presence of ANCA autoantibodies, ANCA titers and, the appearance of CD19+ B cells in the circulation as predictors of the risk of disease relapse in AAV patients. The study found that ANCA negativity regardless of B cell presence was a strong predictor that disease remission would be maintained. Additionally, PR-3 ANCA positivity or persistence of PR-3 ANCA levels was a strong predictor of relapse. Relapses in the MPO-ANCA population occurred exclusively when B cells were present. This research provides the interesting possibility that a tailored regimen of therapy based on ANCA positivity and presence of B cells could be effective in preventing disease relapse in AAV patients. The question that remains is if this method could lead to overtreatment, as some patients are able to achieve clinical remission despite ANCA positivity and relapses have been known to occur in patients regardless of B cell presence. This will be an interesting topic of further research^[40].

Conclusion

Treatment of AAV has always provided a challenge for physicians both because of its severe, life threatening manifestations and, the multitude of side effects caused by the cytotoxic medications needed to induce and maintain disease remission. Despite these therapies, patients with AAV still experienced high rates of relapse. Cyclophosphamide was the gold standard of induction therapy for many years however, given its extensive risk of cytotoxic side effects, it was not an ideal long-term maintenance therapy for patients with AAV and other agents were explored for disease maintenance remission. Among these medications are MTX and AZA, which gained recognition for their ability to induce disease remission and shorten the length of time of CYC exposure, however, these medications had high relapse rates and were associated with numerous adverse effects. The RAVE and RITUXVAS trials demonstrated that RTX was non-inferior to CYC in successfully achieving disease remission in AAV patients and, had a similar safety profile to CYC.

After the discovery that RTX was a promising induction agent for AAV, early retrospective reviews were conducted exploring RTX as a maintenance therapy for AAV. The MAINRITSAN trial provided evidence of the superiority of RTX to AZA in preventing disease relapse in AAV patients, and the MAINRITSAN 2 trial demonstrated that individually tailored regimens of RTX infusions based on the reappearance of ANCA autoantibodies, increase of ANCA titers or, reappearance of CD19+ B lymphocytes from treatment randomization had similarly low relapse rates as fixed dose regimens of RTX and, enabled patients to receive fewer infusions. The RITAZAREM trial demonstrated the superiority of RTX as a maintenance therapy compared to AZA in the prevention of disease relapse in patients with a history of relapsing AAV and, showed that RTX had fewer associated adverse events. Additionally, despite being left out of the above trials due to its distinct pathogenesis, RTX maintenance was also investigated in EGPA as compared to CYC in another study and was deemed an effective and well tolerated treatment option for EGPA.

These studies are monumental in the advancement of therapy for AAV because up until recently, the gold standard induction therapy for this disease was extremely cytotoxic and even though alternate maintenance strategies were aimed at reducing the toxic effects of CYC, they had high rates of relapse and were associated with adverse effects of their own. The above literature reveals that RTX is a safe, effective and well tolerated induction and maintenance therapy in AAV that can be given in a tailored dosing regimen, thus exposing patients to fewer infusions. This has important implications in the treatment of AAV as patients treated with RTX will have better disease control with lower relapse rates, fewer exposures to the medication and, a decreased incidence of adverse events. As a result, patients with AAV receiving RTX therapy will have higher survival rates and longer relapse free periods, leading to an overall enhanced quality of life and improvement in patient outcomes.