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Keywords:

  • rituximab;
  • PML;
  • ITP;
  • infections;
  • hepatitis B

Summary

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

Depletion of B lymphocytes using the anti-CD20 monoclonal antibody rituximab has wide-spread use in the treatment of patients with autoimmune disorders. As haematopoietic progenitor cells and only a fraction of differentiated plasma express CD20, the effect of rituximab on immune function appears to be minimal. However, hypogammagobulinaemia can occur with repeated doses and emerging data from large studies suggest a subtle increase in the risk of infection. Reactivation of latent JC virus, resulting in progressive multifocal leucoencephalopathy, and hepatitis B virus, resulting in hepatoxicity, have been documented in patients receiving rituximab; although confounding effects of concomitant immunosuppressive therapies and immune dysregulation due to the underlying disease make causal associations of infections problematic. This review discusses the efficacy of B cell depletion therapy in the treatment of autoimmune diseases, the effect of B cell depletion on infection and immunity including the role of the B cell in autoimmunity, and identifies areas of controversy.

Host defence involves the complex coordination of innate immunity, specific antibody response and stimulation signals from effector and suppressor cells. Normally, this network results in effective rejection of foreign invaders and tolerance to self. In autoimmune conditions, self-tolerance is lost either to specific targets, such as platelets in immune thrombocytopenic purpura (ITP), or to host tissues, as in systemic lupus erythematosus (SLE), due to acquired dysfunction of the interaction between immune cells. Pathological self-directed antibodies are presumed to be a hallmark, if not a cause of autoimmune diseases even though specific autoantibodies are often elusive and a causal relationship is difficult to confirm.

On the premise that auto-reactive CD20-positive B lymphocytes contribute to the loss of self tolerance, the anti-CD20 monoclonal antibody rituximab has been widely used in patients with various autoimmune diseases including rheumatoid arthritis (RA), an indication for which the drug is now licenced (Leandro et al, 2002a; Edwards et al, 2004a; Popa et al, 2007), ITP (Arnold et al, 2007; Godeau et al, 2008), other immune mediated haematological conditions, such as autoimmune haemolytic anaemia and thrombotic thrombocytopenic purpura (TTP), and autoimmune neurological, renal and dermatological conditions (reviewed in McDonald & Leandro, 2009). Rituximab rapidly depletes CD20+ B-lymphocytes, presumably resulting in the interruption of the pathological cell linage responsible for autoantibody production. This article reviews the activity and mechanism of action of rituximab in autoimmune diseases and discusses the potential effects of depletion of B lymphocytes on infection and immunity.

Rituximab efficacy in non-malignant diseases

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

Rituximab was originally developed for the treatment of lymphoma (Maloney et al, 1997; McLaughlin et al, 1998) as targeted therapy against malignant B-lymphocytes. Subsequently, because of the rapid depletion of autoantibody producing B-lymphocytes and following resolution of joint inflammation in a patient with lymphoma treated with rituximab, its use was proposed in RA (Protheroe et al, 1999). The authors described good responses (Edwards & Cambridge, 2001) and subsequent randomised controlled studies have shown response rates of 51% and 85% (Edwards et al, 2004a; Cohen et al, 2006).

In patients with SLE, a randomised double-blind placebo controlled phase II/III trial failed to meet its endpoints of a major or partial clinical response over 52 weeks (Albert et al, 2008). However, non-controlled studies have shown benefit, including a retrospective analysis of 50 patients with SLE treated at one centre over a 7-year period demonstrating that 47% of patients achieved at least partial remission after 1 cycle of rituximab (Lu et al, 2009). Other studies describe improvement in skin rashes, mouth ulcers, serositis, neurological symptoms, autoimmune cytopenias, lung disease, vasculitis, arthralgia and arthritis (Leandro et al, 2002b, 2005; Looney et al, 2004; Sfikakis et al, 2005; Tokunaga et al, 2007; Reynolds et al, 2009).

In neurological disorders, a phase II placebo-controlled multicentre trial of 104 patients with multiple sclerosis given two doses of rituximab (1 g on days 1 and 15), demonstrated reduced numbers of gadolinium-enhancing lesions at weeks 12, 16, 20, 24 and 48 compared to control (P < 0·01). In addition, relapse rates were lower at week 24 (14·5% vs. 34·3%, P = 0·02) and at week 48 (20·3% vs. 40%, P = 0·04) (Hauser et al, 2008). Multiple sclerosis has been thought to be primarily T cell-mediated; yet, the success of B lymphocyte depletion therapy reinforces the (direct or indirect) role of B lymphocytes in autoimmunity.

A recent review described the use of rituximab in numerous other non-haematological diseases including Sjorgren syndrome, anti-neutrophil cytoplasmic antibody-associated vasculitis, mixed cryoglobulinaemia, solid organ transplantation, renal disease, neurological diseases including myasthenia gravis and dermatological conditions (McDonald & Leandro, 2009).

Even though the use of rituximab for autoimmune diseases is widespread, other than lymphoma, RA is the only licenced indication.

Rituximab efficacy in ITP

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

Rituximab was found to be moderately effective in a systematic review of reports of non-randomized studies in ITP (Arnold et al, 2007). Of 313 patients, half of whom were splenectomized, 62·5% (95% confidence interval [CI]: 52·6–72·5%) achieved a platelet count response (platelet count >50 × 109/l). Median time to response was 5·5 weeks (range 2–18) and median duration of response was 10·5 months (range 3–20). Rituximab has also been investigated in the early stages of ITP as a means of averting splenectomy in a single-arm study from France that enrolled 60 non-splenectomized patients (Godeau et al, 2008). A good response, defined as a platelet count 50 × 109/l or more with at least a doubling from baseline, was obtained in 40% of the patients (24/60 [95% CI: 28–52%]) at 1 year and in 33·3% (20/60 patients) at 2 years after rituximab (375 mg/m2 weekly for 4 weeks). Sixteen patients experienced transient side effects, but only one discontinued treatment because of serum sickness. There were eight severe adverse events judged not to be related to rituximab including fatal myocardial infarction (n = 1), atrial fibrillation (n = 3), malignancy (n = 2), Guillain–Barre syndrome (n = 1) and renal colic (n = 1). Finally, in a randomized trial (published in abstract only) comparing dexamethasone and dexamethasone plus rituximab in patients with previously untreated ITP (n = 101), a platelet count response (>50 × 109/l) at 6 months was achieved by 36% of patients on dexamethasone alone, and 63% of patients on dexamethasone plus rituximab (P = 0·004). Many patients (27 of 49 patients) crossed over to the rituximab arm (Zaja et al, 2008). Responses were maintained after a median follow up of 18 months in most patients.

Rituximab is also useful in children with ITP. Bennett et al (2006) reported on the efficacy of rituximab in 36 children with ITP treated with rituximab, 11 of whom had undergone splenectomy; only 11 of 36 (31%) achieved a platelet count response by week 12. In a recent report, Mueller et al (2009) reported on the long term follow up of those children; by 1 year, three of 11 children had relapsed, and there were three additional late responders. Thus, overall the rate of response to rituximab in children with ITP was approximately 30% after 1 year. Early response rates appear to be lower in children, although by 1 year, response rates appear to be similar than adults, (Godeau et al, 2008).

Mechanism of action of riuximab

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

Rituximab is a chimeric anti-CD20 monoclonal antibody that causes the rapid depletion of CD20+ B-lymphocytes. Probably the main mechanism of action of rituximab is antibody-dependent cell-mediated cytotoxicity (ADCC), a process by which innate effectors, such as monocytes and macrophages, are recruited cells via Fc and FcγR interactions (Hamaguchi et al, 2006; Kaneko et al, 2006) leading to the release of proinflammatory or cytotoxic cytokines, proteases and reactive oxygen species, ultimately resulting in the lysis of target B cells (Glennie et al, 2007). Rituximab (IgG) – coated B cells may also be internalized by phagocytosis as part of the ADCC process. The efficacy of such Fc-mediated cell clearance depends on characteristics of the effector cell FcγR phenotype as well as the B cell circulatory microenvironment; B lymphocyte clearance appears to be most efficient in patients with FcγRIIIA V polymorphisms (Cartron et al, 2002; Anolik et al, 2003) and least efficient in anatomical locations where B lymphocytes circulate only rarely, as in the lymph nodes and peritoneal cavity (Gong et al, 2005). Pure FcR blockade is probably a less important mechanism of rituximab, but it may explain the rapid responses that have been observed (Cooper et al, 2004). Complement-dependent cytotoxicity is another mechanism of action of rituximab (Cragg & Glennie, 2004) leading to direct B cell lysis. Finally, binding of rituximab to CD20 can induce intracellular signals that trigger cell cycle arrest and programmed cell death, as in apoptosis assays of chronic lymphocytic leukaemia cells in vitro (Byrd et al, 2002).

Potency of rituximab

Expression of CD20 begins at the pre-B cell stage (before IgM expression) and is lost prior to differentiation into immunoglobulin-secreting plasma cells (Pescovitz, 2006). Thus, CD20 is not significantly expressed on hematopoietic progenitor cells or on mature, antibody-secreting plasma cells (Uchida et al, 2004). The activity of rituximab is related to several characteristics of the CD20 molecule and the drug itself. First, CD20 is expressed at high levels, often with more than 250 000 molecules per cell; second, rituximab is not internalized after binding to CD20; third, CD20, a molecule with four membrane-spanning domains and two cytoplasmic domains, is deeply anchored into the cell membrane and resistant to antigen shedding; and fourth, the two extracellular loops on the CD20 molecule, which make up the antigenic target for rituximab, do not extend far from the cell surface (Einfeld et al, 1988; Stamenkovic & Seed, 1988). As a result, anti-CD20 antibody clusters densely and persistently close to the cell surface facilitating the recruitment of complement and direct cell lysis. Rituximab also has the ability to organize CD20 molecules into microdomains or lipid rafts facilitating complement activation (Cragg & Glennie, 2004).

Immunological effects of rituximab

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

B-cell depletion following rituximab treatment frequently lasts for longer than 6 months, after which a new ontogeny repopulates the B cell pool characterized by the appearance of immature (CD38++, CD10+, CD24+), followed by naïve (CD27) B cells, while CD27+ memory B cell may remain reduced for up to 2 years (Leandro et al, 2006, 2007; Roll et al, 2008). Early repopulation of an expanded population of highly mutated B cells with plasmablast phenotype suggests a T cell-induced mutational pattern (Palanichamy et al, 2008). As expression of CD20 begins in the late pre-B cell phase, rituximab interrupts the generation of plasmablasts from memory B cells (Hoyer et al, 2005) and may interfere with the survival of long-lived, CD20+ plasma cells in secondary lymphoid tissue as described in a xenograft model (Withers et al, 2007); due to the location of plasma cells, human models of the effect of rituximab on mature cells are limited.

The depletion of CD20+ B-cell has direct effects on antibody production, and indirect effects on cellular immunity. Both are likely to be important in the mechanism of action of rituximab in autoimmune diseases. The influences of B cells in autoimmunity are presented in Table I.

Table I.   Role of B-lymphocytes in the development of autoimmunity.
B cell functionEffect – disease examples
  1. ITP, immune thrombocytopenic purpura; SLE, systemic lupus erythematosus; IL, interleukin; INFγ, γ-interferon; TNFα, tumour necrosis factor α; Th, T helper cell; TGFβ, transforming growth factor β.

AutoantibodiesActivating receptors – Graves disease
FcR mediated phagocytosis- ITP
Inhibiting enzyme activity- TTP
Inhibiting receptors- Myasthenia Gravis
Immune complex formation- SLE
Antigen presentationActivation of autoreactive T cells- Multiple sclerosis, diabetes
Cytokine productionIL2, INFγ, TNFα– Th1 stimulation (inflammation)
IL6, TGF-β– Th17 stimulation
Regulatory B cellsIL10 – restores Th1/Th2 balance
TGFβ– apoptosis of effector T cells
Regulatory antibodies – neutralizing and inhibitory (FcRIIb)
Recruitment of regulatory T cells

Effect on autoantibody production

B-1 cells in mice and marginal zone (MZ) B cells produce natural antibodies, make antibody responses to microbial pathogens, and contribute to autoimmunity (Durand et al, 2009). This depletion of memory B cells and MZ B cells following rituximab with preservation of plasma cells may have a selective effect on auto-antibody secretion, accounting for the preservation of humoral immunity in the face of resolution of auto-immunity. In 16 patients with SLE, antinucleosome and anti-dsDNA antibodies decreased by 6–8 months after rituximab, yet levels of other autoantibodies (anti-histone and anti-SSA) and levels of microbial antibodies (anti-pneumococcal and anti-tetanus) did not change. Greater decreases in antibody levels were seen in patients who had a prolonged remission compared to those who relapsed within a year (Cambridge et al, 2006). This has also been reported in patients treated with rituximab for active vasculitis, with a fall in IgG anti-proteinase-3 but no fall in levels of natural antibody – isohemagglutinins or antibodies to thymus-dependent or -independent extrinsic antigens(Ferraro et al, 2008). Similarly, in patients with TTP, response to rituximab was associated with a reduction of IgG inhibitory activity to ADAMTS13 (Scully et al, 2007). We have reported in abstract form (Cooper et al, 2002) that responses to rituximab in ITP are sometimes associated with a decrease in anti-platelet antibodies (APAs), however, some patients without detectable APAs still responded to rituximab and non-responders had variable responses in their APAs (data not published). Furthermore, no changes in circulating anti-thyroglobulin, anti-thyrperoxidase or anti-thyroid-stimulating hormone receptor antibodies despite responses to rituximab were shown in patients with Grave’s disease and orbitopathy (Salvi et al, 2009). These data, together with the responses seen in patients with previously considered T cell-mediated autoimmune diseases, such as MS, suggest that reduction in auto-antibodies may not be the prime effect of rituximab in all diseases.

Rituximab-induced T cell changes

Removal of the CD20+ B-cell pool indirectly causes the normalization of other cellular immune defects including the restoration of the T-helper cell type 1 (Th1)/Th2 ratio, loss of T cell VB skewing, increased expression of Fas ligand and BCL2 mRNA, decreased expression of BAX mRNA in T-helper cells and increased numbers of regulatory T cells in patients with ITP who responded to rituximab (Stasi et al, 2007, 2008). T cell changes, including increase in regulatory T cells as well as activated T cells, have been noted after rituximab in patients with SLE (Sfikakis et al, 2007; Vallerskog et al, 2007) but not necessarily in patients with RA (Feuchtenberger et al, 2008). Baseline T cell abnormalities in ITP also appear to influence responses to B cell depletion; patients with ITP who have large numbers of abnormal complimentarity-determining region 3 were less likely to respond to rituximab (Stasi et al, 2007).

Although variable changes in T lymphocytes have been described following rituximab, these studies suggest that in addition to antibody formation, B cells may have indirect effects on cellular immunity. A mouse model exploring the effect of B cell depletion on T cells demonstrated no direct effect on T cell subsets or activation status, and no effect on CD8+ T cell activation but an impairment in CD4+ T cell activation and clonal expansion in response to protein antigens and pathogen challenge. In this model the combination of B cells and dendritic cells were required for optimal antigen-specific CD4+ T cell priming. B cell depletion therapy was also able to inhibit antigen-specific CD4+ T cell expansion in both collagen-induced arthritis and autoimmune diabetes mouse models, providing direct evidence that B cells contribute to T cell activation and expansion in vivo (Bouaziz et al, 2007).

In a recent review, Edwards and Cambridge (2005) suggested that depletion of the B cell as the antigen presenter is not enough to stop autoimmunity, given the continued presence of dendritic cells. They commented on the association between autoantibody decline and clinical responses in patients with RA and suggested that the confusion of timings of response and delayed relapses – up to 2–4 years after B cell return – relates to a vicious cycle of antibody production and T cell activation, which is terminated when the B cell is depleted and takes its time to come back (Edwards & Cambridge, 2005). While relevant in RA, we suggest that the different timings of responses seen in patients with ITP – one-third responding within 1 week, one-third within 4–6 weeks and one-third having a very slow increase in their platelet count (Cooper et al, 2004) – may in fact relate to different activities of the B cell in autoimmunity. This is an area not yet fully explored.

In a similar fashion, a number of review articles and original data from Shomchiks’ group suggest that T–B cell interactions may engender a positive feedback loop that amplifies and sustains autoimmunity. Stimulation through different Toll-like receptors (TLR) may promote (TLR7) or regulate (TLR9) autoimmunity in the B cell, resulting in T cell-independent activation of autoreactive B cells and generation of autoantibodies (Herlands et al, 2008). These activated B cells then break T cell tolerance and establish positive feedback loops between B cells, T cells, dendritic cells resulting in full-blown autoimmunity (Christensen & Shlomchik, 2007; Shlomchik, 2008, 2009).

Regulatory B cells

In addition to producing antibodies and activating T cells through antigen presentation and cytokine release, a proportion of B cells appear to be regulatory, producing quantities of interleukin 10 (IL10). The timing of rituximab use may be important in restoring the balance between effector and regulatory B cells. In a mouse model of multiple sclerosis (the EAE mouse model), while depletion of B cells after antigen stimulation abrogates the inflammatory response to this antigen, B cell depletion before antigen stimulation results in an exacerbation of the immune response. The increased symptom severity and increased T cell influx into the central nervous system when B cell depletion was instituted before EAE initiation is thought to be related to depletion of IL10 producing CD1dhiCD5+ regulatory B cells. Transfer of these cells after B cell depletion and before initiation of EAE normalized the responses (Matsushita et al, 2008).

In another mouse model, B cell depletion could prevent, delay and even reverse diabetes after frank hyperglycemia through expansion of both regulatory T and regulatory B cells (Hu et al, 2007).

Patients with more prolonged B cell depletion are more likely to respond than those in whom B cell return is early (Cooper et al, 2004) and B cell depletion appears to be better in SLE and lymphoma patients with the FcRIIIa V polymorphism (Anolik et al, 2003). These immunological biomarkers may be useful for the assessment of rituximab suitability in patients with autoimmune disease in the future.

Other immunological effects

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

Cytopenias following rituximab

Rituximab can induce both neutropenia and thrombocytopenia (Cattaneo et al, 2006). While thrombocytopenia is uncommon and usually mild, case reports show this can be severe (Larrar et al, 2006; Dhand & Bahrain, 2008; Ram et al, 2009; Yi et al, 2009). This should be considered when rituximab is given for ITP. Neutropenia following rituximab has been more extensively reported. It is frequently of late onset (>4 weeks after treatment) and can occur when rituximab is used on its own, although it is more common in patients treated with both rituximab and chemotherapy occurring in up to 25% of cases (Nitta et al, 2007). The cause of late onset neutropenia is not clear, but patients show maturation arrest (Tesfa et al, 2008) and high levels of B-cell activating factor, suggesting it may be related to haematopoietic stem cell competition (Terrier et al, 2007). Neutropenia has been reported in patients receiving rituximab for autoimmunity, although this is less common. We found no fall in neutrophil levels in 57 patients treated with a single course of rituximab for ITP (Cooper et al, 2004).

Immunoglobulin levels after rituximab

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

Immunoglobulin levels do not fall below normal levels in the majority of patients treated with one course of rituximab (Stasi et al, 2001). However, with increasing courses of rituximab, which may be required in relapsing/remitting diseases, hypogammaglobulinaemia has been known to occur (Edwards et al, 2006) especially in patients who are also treated with chemotherapy or bone marrow transplantation (Nishio et al, 2006; Lim et al, 2008). Hypogammaglobulinaemia has been reported in patients treated for autoimmunity (Nishio et al, 2005; Edwards et al, 2006; Keystone et al, 2007). It may also occur more commonly in children, who have an immature immune system, and in patients with underlying T cell abnormalities (Cooper et al, 2009) with one series reporting 3 of 12 patients developing hypogammaglobulinaemia after a single course of rituximab in patients with ITP associated with autoimmune lymphoproliferative disorder (Rao et al, 2009). It has also recently been noted that IgM levels fall more than IgG levels, with a 10% fall after the first course, 19% after the second and 24% after the third, as reported in an open-label extension of three controlled trials including 1669 patient-years. In contrast, IgG and IgA only fell by 2% and 4%– although few fell below normal levels (Keystone et al, 2007).

Risk of infections

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

The incidence of infection has been reported to be increased in some studies but not others (Rafailidis et al, 2007). In the systematic review of rituximab in ITP (Arnold et al, 2007), 7 of 303 treated patients (2·3%) developed serious infections, four of which were fatal; however a causal association could not be confirmed and the majority of patients had received additional immunosuppressive therapies. In a randomized trial of patients with RA (n = 520), 5·2 serious infections per 100-patient-years occurred in the rituximab group compared with 3·7 in controls (Cohen et al, 2006); and in another trial (n = 161), 5·0% of treated patients developed serious infection compared with 2·5% of controls (Edwards et al, 2004b) (test of significant not given). Even in patients with lymphoma, a recent trial of rituximab maintenance (n = 167) administered every 3 months for up to 2 years, uncovered a higher frequency of serious infections in treated patients compared with those on observation (9% vs. 2·4%; = 0·009) (van Oers et al, 2006). Similarly, in patients with HIV-lymphoma, rituximab may be associated with an increased risk of bacterial and opportunistic infections (Kaplan et al, 2005). On the other hand, a systematic review of rituximab in cancer patients did not show an increased risk of infection (Rafailidis et al, 2007). Randomized trials and meta-analyses may not detect subtle differences in infectious complications; this will require long term follow up data.

Progressive multifocal leucoencephalopathy

One rare life-threatening infection that has been potentially linked to rituximab is progressive multifocal leucoencephalopathy (PML), which led to a black box warning issued by the US Federal Drug Administration (FDA). PML is a rare demyelinating disease caused by reactivation of latent JC virus (JCV) in the brain. The syndrome is characterized by rapidly progressive neurological symptoms including weakness or paralysis, vision loss, impaired speech and cognitive deterioration. Immunosupression and underlying lymphoma are known risk factors for PML because dormant JCV, present in over 80% of adults, disseminates when normal cellular immune surveillance is compromised (Sabath & Major, 2002). PML has been reported in patients with SLE on many forms of treatment, suggesting that underlying patient characteristics may be more important than the treatment (Calabrese & Molloy, 2008; Molloy & Calabrese, 2008).

A recent report identified 57 patients with PML following rituximab, by surveying 12 cancer centres and academic hospitals in North America (n = 22), reviewing reports to the FDA (n = 11) and the manufacturer (n = 30), and in publications (n = 18) between 1997 and 2008 (Carson et al, 2009). Of 57 patients, 52 had lymphoproliferative disorders, two had SLE, one had RA, one had autoimmune pancytopenia and only one patient had ITP. PML occurred a median of 5·5 months from rituximab (range 0·3–66 months) with a 90% fatality rate. Of the 14 patients tested, nine had CD4 lymphopenia (<0·5 × 109 cells/l) and nine had decreased CD4/CD8 ratios. Notably, only one patient had not received stem cell transplant, purine analogues or alkalating agents and had normal CD4 counts (Carson et al, 2009). Due to confounding variables including the underlying disease and the addition of other immunosuppressive treatments, a causal relationship between rituximab and the development of PML cannot be confirmed but careful consideration of the use of this therapy and vigilence for its effects is required.

Hepatitis B reactivation

Reactivation of hepatitis B virus (HBV) is a well recognized complication of immunosuppressant or cytotoxic therapies with or without rituximab (Coiffier, 2006). These drugs interfere with normal immune surveillance resulting in increased levels of replicating virus and widespread infection of hepatocytes. Once immune modifying therapy is withdrawn, immune competence is restored and infected hepatocytes are rapidly destroyed, leading to liver damage, which can be fatal (Perrillo, 2001). The response is primarily mediated by CD8+ cytotoxic T-lymphocytes (Yang et al, 1988).

The frequency of HBV reactivation is 20–50% among hepatitis B surface antigen (HBsAg)-positive individuals receiving chemotherapy or immunosuppressants with an associated mortality of 10–40% (Sarrecchia et al, 2005). Patients with lymphoma appear to be more at risk for HBV reactivation than patients with other cancers because of the greater degree of immunosuppression (Liang, 2009), and rituximab may be more of a risk factor than standard chemotherapy alone (Coiffier, 2006). A recent report described 46 patients with non-Hodgkin lymphoma and remote HBV infection (HBsAg-negative/hepatitis B core antibody (HBcAb)-positive) receiving chemotherapy (Yeo et al, 2009). Of the 21 patients who received chemotherapy (CHOP; cyclophosphamide, doxorubicin, vincristine, prednisone) plus rituximab (CHOP-R), five reactivated HBV infection, including one patient who died of liver failure (Yeo et al, 2009); whereas, of the 25 patients treated with CHOP alone, none reactivated. Patients with rheumatological disease receiving immunosuppressive therapy are also at risk of HBV reactivation, especially after treatment with rituximab or other biological agents (Robinson & Walker-Bone, 2009).

A recent report examined liver-related outcomes among 456 consecutive patients treated with rituximab for any indication (Hanbali & Khaled, 2009). Of the 32 HBV seropositive patients, 14 (43·8%) received rituximab monotherapy including 10 patients with autoimmune disease. There were 11 (34·4%) liver events, ranging from elevation of liver enzymes to hepatic failure. Of six patients with remote infection, 2 (33·3%) developed hepatic events most of which were mild. The mean duration of onset of acute liver events after rituximab was 6·2 months.

Published recommendations for patients with haematological malignancy support universal screening for HBV. Patients who are HBsAg-positive should receive antiviral prophylaxis with lamivudine, continued for at least 6 months after the cessation of chemotherapy (Lok & McMahon, 2004; Liang, 2009), and patients with remote infection should be closely monitored. In patients with rheumatological diseases, lamivudine prophylaxis has been recommended for the following patient groups: (i) all active carriers (HBsAg-positive with evidence of viral repliction) receiving immunosuppressants, disease modifying antirheumatic drugs (DMARDS) or biological agents (Zingarelli et al, 2008), (ii) inactive carriers (HBsAg-positive without evidence of replication) receiving biological agents, immunosuppressants or high dose corticosteroids for prolonged periods, and (iii) occult carriers (HBsAg-negative, HBcAb-positive) receiving rituximab (Tsutsumi et al, 2005).

Other infectious complications

Numerous case reports describe cases of unusual viral infections. A review of the literature by (Aksoy et al, 2007) reported 64 cases of serious viral infections after rituximab treatment, including hepatitis B (n = 25), cytomegalovirus infections (n = 15), varicella zoster virus (n = 6) and other viruses (echo virus, influenza A, Parvovirus, respiratory syncytial virus, West nile, BK virus, enterovirus, hepatitis C virus, herpes simplex virus, JCV n = 18). Approximately 33% of non-HBV infections resulted in death (Aksoy et al, 2007). Another report compared the incidence of infections in 77 patients receiving rituximab following renal transplant, to 909 patients with no rituximab following renal transplant between April 2004 and August 2008 (Kamar et al, 2009). After a median follow-up of 16·5 (1–55) months for rituximab patients and 60·9 (1·25–142·7) months for control patients, the incidence of bacterial infection was similar between the two groups, the viral-infection rate was significantly lower, and the rate of fungal infection was significantly higher in the rituximab group. Seven deaths (9·09%) were related to an infectious disease in the rituximab-treated patients, compared to 1·55% in the controls (P = 0·0007). Independent predictive factors for infection-induced death were the combined use of rituximab and antithymocyte-globulin given for induction or anti-rejection therapy, recipient age, and bacterial and fungal infections. However, although the conclusions from this study were that after kidney transplantation, the use of rituximab is associated with a high risk of infectious disease and death related to infectious disease, the indications for rituximab, such as rejection, are confounding factors (Kamar et al, 2009).

Other infections common in individuals with immunodeficiency have also been reported; two cases of severe nontuberculous mycobacterial infections following rituximab for refractory myositis (Lutt et al, 2008) and a higher incidence of fungal infection was described in elderly patients (>80 years) receiving rituximab with combination chemotherapy (CHOP) (Lin et al, 2007).

Effect of rituximab on vaccine response

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

The influence of rituximab on vaccine responses continues to be debated, with some studies suggesting that the humoral immune response to vaccines following rituximab treatment is impaired (van der Kolk et al, 2002; Horwitz et al, 2004) while others do not (Hassan et al, 2004; Oren et al, 2008). Horwitz et al (2004) observed an inadequate antibody response to pneumococcal polysaccharide (a T-cell independent antigen), and a preserved response to tetanus toxoid (TT) (a T-cell dependent antigen) following rituximab in 35 lymphoma patients previously treated with high dose chemotherapy. In a similar patient group, van der Kolk et al (2002) observed a reduced recall response to TT and polio, and absent primary response to keyhole limpet hemocyanin (KLH) and hepatitis A. These studies were confounded by cytotoxic treatments and underlying lymphoma and lacked adequate controls. Bearden et al (2005) immunized 18 dialysis patients with phiX174, a bacteriophage that elicits a B and T cell response, and showed that rituximab therapy resulted in inhibition of antibody formation following primary (at 2 weeks) and secondary (at 8 weeks) immunizations. In contrast, Oren et al (2008) reported that rituximab did not impair an adequate response to 2 of 3 influenza virus antigens in patients with RA (n = 14), even during profound B cell depletion.

There is conflicting data on the effect of rituximab on the response to antigen by humoral and cellular pathways. These concerns are especially pertinent to ITP patients who rely on vaccines prior to splenectomy. The manufacturer recommends that vaccines should be administered 4 weeks prior to the first dose of rituximab, which may not be practical for all patients. Further studies on the effect of rituximab on antigen response are needed.

Discussion

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References

The depletion of B cells in the peripheral blood following rituximab appears to be directly linked to its efficacy in patients with autoimmune diseases. The expression of CD20 on memory B cells and hence their depletion with rituximab may result in the selective depletion of autoantibodies as reported in patients with SLE. However, there is significant evidence that other factors, such as the loss of T cell stimulation by the autoreactive B cell pool either by antigen presentation or by the production of immunomodulatory cytokines, may be the main mechanism of effect of rituximab in patients with autoimmunity. This and the subtle evidence of increased infections, such as re-activation of HBV and reports of PML, especially when rituximab is used in conjunction with other immunosuppressive agents, show that B cells are not only antibody producers, but also a crucial arm of the immune system in orchestrating normal antigen responses and in stimulating T cells.

Rituximab has been used to treat countless patients with lymphoma and autoimmunity and the complication rate, including the incidence of infectious complications, appears to be low and may not be as significant as other therapies, such as long-term steroids.

A number of issues remain to be resolved. First, when is the optimal timing of rituximab administration in patients with ITP, RA or other autoimmune diseases? Evidence from clinical studies (Cooper et al, 2004; Zaja et al, 2006) suggest that rituximab may be more effective if given early, and that the effect is diminished once marked abnormalities in T cells are already present (Stasi et al, 2007). Similarly, early administration as a prevention for the development of chronic ITP, may be more likely to establish tolerance. Second, what is the optimal dose and schedule for rituximab in autoimmune diseases? The dose for autoimmunity was borrowed from the lymphoma indication, but without the need to eliminate a tumour mass, likely lower doses would be just as effective (Provan et al, 2007). The least amount of B cell depletion needed to achieve a response while limiting susceptibility to infection is not yet known. Third, what precautions should be taken for patients receiving rituximab? We propose that all patients should be screened for hepatitis B; it may be more appropriate for those with a positive screen to avoid rituximab for indications in which efficacy has not been established in clinical trials. If treatment is unavoidable, patients with active hepatitis should receive prophylaxis with lamivudine, and careful monitoring should be instituted for patients with occult (remote) infections. There is no evidence that prophylaxis against other infections with either intravenous immunoglobulin or antivirals should be used, however, it may be prudent to avoid rituximab during or immediately following any viral infections. The thrombocytopenia that can occur after rituximab and the delay in response prompts us to suggest that in patients with severe thrombocytopenia, additional therapy should be used to cover this period. The late onset of neutropenia seen in some patients improves over time and no therapeutic intervention has been found to speed recovery (Lai et al, 2009). Fourth, what is the effect of rituximab on vaccine responses? Given that suboptimal responses to vaccination have been documented, and that many patients with ITP may need splenectomy, routine vaccinations against Spneumomia, Nmeningitides, and Hinfluenza type B seems appropriate when feasible before the use of rituximab. A summary of recommended investigations and management of adverse events of rituximab is shown in Table II.

Table II.   Recommended investigations and management of adverse events of rituximab.
RiskSuggested management
  1. PML, progressive multifocal leucoencephalopathy; IVIG, intravenous immunoglobulin.

Hepatitis B re-activationIf treatment is unavoidable, patients with active hepatitis should receive prophylaxis with lamivudine; patients with occult infections, should be monitored for re- activation
Reduced immunoglubulinsRegular monitoring of IgG levels; consider replacement with IVIG for symptomatic infections
Suboptimal vaccine responseVaccinate pre-rituximab; verify specific antibody response to vaccine
PMLInformed patients of potential risk; Prompt investigation of abnormal neurological symptoms

Finally, the lasting effects of rituximab on both the humoral and cellular arm of the immune system need further investigation. Given that few patients enter a long-term remission, and repeated doses are often required, more problems following repeated B cell depletion may be encountered in the future.

References

  1. Top of page
  2. Summary
  3. Rituximab efficacy in non-malignant diseases
  4. Rituximab efficacy in ITP
  5. Mechanism of action of riuximab
  6. Immunological effects of rituximab
  7. Other immunological effects
  8. Immunoglobulin levels after rituximab
  9. Risk of infections
  10. Effect of rituximab on vaccine response
  11. Discussion
  12. Acknowledgements
  13. Funding
  14. References
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