B‐cell Therapy for Multiple Sclerosis: Entering an era

Monoclonal antibodies that target CD20 expressing B cells represent an important new treatment option for patients with multiple sclerosis (MS). B‐cell‐depleting therapy is highly effective against relapsing forms of the disease and is also the first treatment approach proven to protect against disability worsening in primary progressive MS. Moreover, evolving clinical experience with B‐cell therapy, combined with a more sophisticated understanding of humoral immunity in preclinical models and in patients with MS, has led to major progress in deciphering the immune pathogenesis of MS. Here, we review the nuanced roles of B cells in MS autoimmunity, the clinical data supporting use of ocrelizumab and other anti‐CD20 therapies in the treatment of MS, as well as safety and practical considerations for prescribing. Last, we summarize remaining unanswered questions regarding the proper role of anti‐CD20 therapy in MS, its limitations, and the future landscape of B‐cell‐based approaches to treatment. Ann Neurol 2018;83:13–26     

CD19 as a molecular target in CNS autoimmunity

Multiple sclerosis (MS) and neuromyelitis optica (NMO) are the most prevalent neuroinflammatory diseases of the central nervous system (CNS). The immunological cascade of these disorders is complex, and the exact spatial and temporal role of different immune cells is not fully understood. Although MS has been considered for many years to be primarily T cell driven, it is well established that B cells and the humoral immune response play an important role in its pathogenesis. This has long been evident from laboratory findings that include the presence of oligoclonal bands in the CSF. In NMO, the importance of the humoral immune system appears even more obvious as evidenced by pathogenic antibodies against aquaporin 4 (AQP4). Besides their capacity to mature into antibody-producing plasma cells, B cells are potent antigen-presenting cells to T lymphocytes and they can provide soluble factors for cell activation and differentiation to other immune-competent cells. In MS and NMO, there are substantial data from clinical trials that B cell depletion with CD20-directed agents is effective and relatively safe. Plasma cells, which produce antibodies against molecular targets expressed by the host, but which also provide humoral immune responses against pathogens, are not targeted by anti-CD20 therapies. Therefore, the depletion of CD19-expressing cells would offer potential advantages with regard to efficacy, but potentially higher risks with regard to infectious complications. This review will outline the rationale for CD19 as a molecular target in CNS autoimmunity. The current stage of drug development is illustrated. Potential safety concerns will be discussed.     

A Milestone in Multiple Sclerosis Therapy: Monoclonal Antibodies Against CD20—Yet Progress Continues

Multiple sclerosis (MS), which is a chronic inflammatory disease of the central nervous system, still represents one of the most common causes of persisting disability with an early disease onset. Growing evidence suggests B cells to play a crucial role in its pathogenesis and progression. Over the last decades, monoclonal antibodies (mabs) against the surface protein CD20 have been intensively studied as a B cell targeting therapy in relapsing MS (RMS) as well as primary progressive MS (PPMS). Pivotal studies on anti-CD20 therapy in RMS showed remarkable clinical and radiological effects, especially on acute inflammation and relapse biology. These results paved the way for further research on the implication of B cells in the pathogenesis of MS. Besides controlling relapse development in RMS, ocrelizumab (OCR) also showed clinical benefits in patients with PPMS and became the first approved drug for this disease course. In this review, we provide an overview of the current anti-CD20 mabs used or tested for the treatment of MS—namely rituximab (RTX), OCR, ofatumumab (OFA), and ublituximab (UB). Besides their effectiveness, we also discuss possible limitations and safety concerns especially in regard to long-term treatment, both for this class of drugs overall as well as for each anti-CD20 mab individually. Additionally, we elucidate to what extent anti-CD20 therapy may alter the function of other immune cells, both directly or indirectly. Finally, we cover the current knowledge on repopulation of CD20⁺ cells after cessation of anti-CD20 treatment and discuss future aspirations towards alternative, further developed B cell silencing therapies.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13311-021-01048-z.Key Words: Anti-CD20 treatment, B cells in MS, Ocrelizumab, Rituximab, Ublituximab, Ofatumumab     

Rituximab reduces B cells and T cells in cerebrospinal fluid of multiple sclerosis patients

Effects of B cell depletion by rituximab, a monoclonal antibody to CD20, were studied in patients with relapsing MS that had not responded optimally to standard immunomodulatory therapies. Flow cytometry demonstrated reduced cerebrospinal fluid (CSF) B cells and T cells in most patients at 6 months post-treatment. ELISAs demonstrated modest reductions in serum antibodies to myelin oligodendrocyte glycoprotein and myelin basic protein in some subjects. Beta-interferon neutralizing antibodies were reduced in three subjects, but developed anew after treatment in three others, suggesting caution in considering rituximab as a means to eliminate NABs. In summary, rituximab depleted B cells from CSF at 24 weeks after initial treatment, and this B cell depletion was associated with a reduction in CSF T cells as well.     

The evidence for a role of B cells in multiple sclerosis

Understanding the pathogenesis of complex immunologic disorders such as multiple sclerosis (MS) is challenging. Abnormalities in many different cell types are observed in the immune system and CNS of patients with MS and the identification of the primary and secondary events is difficult. Recent studies suggest that the model of MS as a disorder mediated only by T cells is overly simplistic and propose an important role for B cells in the propagation of the disease. B-cell activation in the form of oligoclonal bands (OCB) production is the most consistent immunologic finding in patients with MS. Notably, markers of B-cell activation within the CSF of patients with MS predict conversion from clinically isolated syndrome to clinically definite MS and correlate with MRI activity, onset of relapses, and disability progression. In addition, the main genetic risk factor in MS is associated with OCB production, and environmental agents associated with MS susceptibility (vitamin D and the Epstein-Barr virus) influence B-cell proliferation and function. Finally, the only cell-specific treatments that are effective in patients with MS are monoclonal antibodies targeting the B-cell antigen CD20, suggesting a potentially causative role for B cells. Based on current evidence there is no longer doubt that B cells are relevant to the etiology and pathogenesis of MS. Elucidating the role of B cells in MS will be a fruitful strategy for disease prevention and treatment.     

Invited article: inhibition of B cell functions: implications for neurology

B cells are involved in the pathophysiology of many neurologic diseases, either in a causative or contributory role, via production of autoantibodies, cytokine secretion, or by acting as antigen-presenting cells leading to T cell activation. B cells are clonally expanded in various CNS disorders, such as multiple sclerosis (MS), paraneoplastic CNS disorders, or stiff-person syndrome, and are activated to produce pathogenic autoantibodies in demyelinating neuropathies and myasthenia. B cell activating factor (BAFF) and a proliferating inducing ligand (APRIL), key cytokines for B cell survival, are strongly unregulated in MS brain and in muscles of inflammatory myopathies. Modulation of B cell functions using a series of monoclonal antibodies against CD20+ B cells or the molecules that increase B cell survival, such as BAFF/APRIL and their receptors BAFF-R, TACI, and BCMA, provide a rational approach to the treatment of the aforementioned neurologic disorders. In controlled studies, rituximab, a B cell-depleting monoclonal antibody, has been encouraging in MS and paraproteinemic anti-MAG demyelinating neuropathy, exerting long-lasting remissions. In uncontrolled series, benefit has been reported in several disorders. B cell depletion is a well-tolerated therapeutic option currently explored in the treatment of several autoimmune neurologic disorders.     

Pathogenic CD8+ T cells in multiple sclerosis

Traditionally, autoimmune pathogeneses have been attributed to CD4⁺ T lymphocytes, as in multiple sclerosis (MS), rheumatoid arthritis, type 1 diabetes mellitus, and/or to B lymphocytes, as in myasthenia gravis and systemic lupus erythematosus. That is because their primary genetic associations are mostly with certain human leukocyte antigen class II alleles, whose gene products present antigens to CD4⁺ T cells. Because few autoimmune diseases show stronger associations with major histocompatibility complex class I alleles (ankylosing spondylitis, Behçet's disease, and psoriasis), CD8⁺ T cells, which interact with major histocompatibility complex class I molecules, have been largely ignored in autoimmunity research. However, a variety of findings has recently revived interest in this population, particularly in MS. First, it shows associations with major histocompatibility complex class I alleles. Second, its lesions show a predominance of CD8⁺ T cells. Third, these represent effectors that can directly damage central nervous system target cells. Furthermore, several clinical trials of monoclonal antibodies specifically against CD4⁺ T cells, or the polarizing cytokines on which they depend, have failed to show any therapeutic benefit in MS, unlike broader‐spectrum antibodies that deplete all T cells. Here, we review the evidence that CD8⁺ T cells play a role in MS pathogenesis. Ann Neurol 2009;66:132–141     

多发性硬化的治疗进展

多发性硬化（MS）是一种常见的中枢神经系统自身免疫性炎性脱髓鞘疾病,自身抗原激活T细胞和B细胞介导的免疫机制异常在MS的致病过程中起重要作用。MS改良治疗（DMTs）可特异性作用于某个与致病机制相关的靶细胞或分子而发挥治疗作用,本文就近年口服药物和单克隆抗体治疗MS的新进展做一综述。     

B cells as a target of immune modulation

B cells have recently been identified as an integral component of the immune system; they play a part in autoimmunity through antigen presentation, antibody secretion, and complement activation. Animal models of multiple sclerosis (MS) suggest that myelin destruction is partly mediated through B cell activation (and plasmablasts). MS patients with evidence of B cell involvement, as compared to those without, tend to have a worse prognosis. Finally, the significant decrease in new gadolinium-enhancing lesions, new T2 lesions, and relapses in MS patients treated with rituximab (a monoclonal antibody against CD20 on B cells) leads us to the conclusion that B cells play an important role in MS and that immune modulation of these cells may ameliorate the disease. This article will explore the role of B cells in MS and the rationale for the development of B cell–targeted therapeutics. MS is an immune-mediated disease that affects over 2 million people worldwide and is the number one cause of disability in young patients. Most therapeutic targets have focused on T cells; however, recently, the focus has shifted to the role of B cells in the pathogenesis of MS and the potential of B cells as a therapeutic target.     

Role of B Cells in Multiple Sclerosis and Related Disorders

The success of clinical trials of selective B‐cell depletion in patients with relapsing multiple sclerosis (MS) and primary progressive MS has led to a conceptual shift in the understanding of MS pathogenesis, away from the classical model in which T cells were the sole central actors and toward a more complex paradigm with B cells having an essential role in both the inflammatory and neurodegenerative components of the disease process. The role of B cells in MS was selected as the topic of the 27th Annual Meeting of the European Charcot Foundation. Results of the meeting are presented in this concise review, which recaps current concepts underlying the biology and therapeutic rationale behind B‐cell–directed therapeutics in MS, and proposes strategies to optimize the use of existing anti–B‐cell treatments and provide future directions for research in this area. ANN NEUROL 2021;89:13–23     

B-cell depletion abrogates T cell-mediated demyelination in an antibody-nondependent common marmoset experimental autoimmune encephalomyelitis model

CD20-positive B-cell depletion is a highly promising treatment for multiple sclerosis (MS), but the mechanisms underlying therapeutic effects are poorly understood. B cells are thought to contribute to MS pathogenesis by producing autoantibodies that amplify demyelination via opsonization of myelin. To analyze autoantibody-nondependent functions of B cells in an animal model of MS, we used a novel T cell-driven experimental autoimmune encephalomyelitis (EAE) model in marmoset monkeys (Callithrix jacchus). In this model, demyelination of brain and spinal cord white and gray matter and the ensuing neurological deficits are induced by immunization with peptide 34 to 56 of myelin/oligodendrocyte glycoprotein (MOG34-56) in incomplete Freund's adjuvant. Although autoantibodies do not have a detectable pathogeniccontribution in the model, depletion of B cells with monoclonal antibody 7D8, a human IgG1κ monoclonal antibody against human CD20, suppressed clinical and pathological EAE. In B cell-depleted monkeys, the activation of peptide-specific Th17-producing and cytotoxic T cells, which in previous studies were found to play an essential role in disease induction, was impaired. Thus, we demonstrate a critical antibody-nondependent role for B cells in EAE, that is, the activation of pathogenic T cells.     

Brain immunohistopathological study in a patient with anti‐NMDAR encephalitis

Background and purpose: Anti‐N‐methyl‐d ‐asparate (NMDA) receptor encephalitis is thought to be antibody‐mediated. To perform an immunohistopathological study of the inflammatory reaction in a brain biopsy performed before immunomodulatory treatments in a patient with anti‐NMDA receptor encephalitis. Methods: An immunohistochemical study was performed using CD3, CD68, CD20, CD138 and CD1a antibodies. Results: Prominent B‐cell cuffing was present around brain vessels accompanied by some plasma cells, while macrophages and T cells were scattered throughout the brain parenchyma. Conclusion: These findings suggest that the B cells interact with the T cells and are involved in antibody secretion by the plasma cells.     

An Update on Monoclonal Gammopathy and Neuropathy

Peripheral neuropathy associated with monoclonal gammopathy is a rare but important cause of neuropathy that can herald serious underlying disease. IgM monoclonal gammopathy of undetermined significance (MGUS) is the most commonly found monoclonal gammopathy associated with neuropathy, with characteristic clinical, electrophysiologic, and pathologic features. The IgG and IgA monoclonal gammopathies are rarely associated with specific neuropathies. Standard immunomodulatory agents including steroids, intravenous immunoglobulin, and plasmapheresis have shown limited efficacy in IgM MGUS. Neuropathies associated with specific lymphoproliferative disorders may not respond to treatments aimed at that disorder. Case series had shown promising results with rituximab, a monoclonal antibody that targets the B cell surface antigen CD20 and results in a rapid and sustained depletion of B cells; however, two recent randomized controlled trials with rituximab failed to provide evidence of efficacy in primary outcome measures, despite reduction in antibody levels. Long-term studies looking at the association between specific immunologic markers and disease recurrence are needed to ultimately develop targeted therapies.     

Failed B cell survival factor trials support the importance of memory B cells in multiple sclerosis

Clinical trials are probably the most informative experiments to help an understanding of multiple sclerosis (MS) biology. Recent successes with CD20‐depleting antibodies have focused attention towards B cell subsets as important mediators in MS. The trial of tabalumab (NTC00882999), which inhibits B cell activation factor (BAFF), is reported and reviewed and this trial is contrasted with the trial on the inhibition of a proliferation‐inducing ligand (APRIL) and BAFF using atacicept (NCT00642902). Both tabalumab and atacicept induce depletion of mature B cells and inhibit antibody formation, but they fail to deplete memory B cells and do not inhibit relapsing MS. Atacicept is reported to augment memory B cell responses and may precipitate relapse, suggesting the importance of APRIL. However, BAFF inhibition can enhance peripheral blood memory B cell responses, which was not associated with augmented relapse. Although other interpretations are possible, these data further support the hypothesis that memory B cells may be of central importance in relapsing MS, as they are the major CD20+ B cell subset expressing APRIL receptors. They also suggest that quantitative and/or qualitative differences in B cell responses or other factors, such as an immune‐regulatory effect associated with APRIL, may be important in determining whether MS reactivates following neutralization of peripheral B cell maturation and survival factors.     

Future research directions in multiple sclerosis therapies

The success of presently available injectable immunomodulatory therapies in treating multiple sclerosis has led to heightened interest in finding even more efficacious and better tolerated therapies. Several oral agents have shown efficacy in phase-II clinical trials and are now entering phase-III pivotal trials. In addition, monoclonal antibodies targeting surface receptors on various cells of the peripheral immune system have also shown efficacy in early studies and will soon be entering phase III. All of these approaches target immune molecules that are not specific for multiple sclerosis (MS) and carry inherent risk of infection and systemic side effects. Novel immunotherapies in preclinical or phases I to IIa testing are attempting to more selectively target pathogenic effector cells and thereby block abnormal immune cell activation without compromising normal healthy immune responses. The induction of tolerance to self-proteins continues to be a goal of MS immunotherapy, but as yet has not been accomplished outside of the laboratory. There is increasing awareness of the need to understand and modulate nonclassical immune targets as well as central nervous system degenerative processes. The roles of vitamins, antimicrobials, and hormones continue to be studied. The mechanisms of neurodegeneration in MS are likely multifactorial and include direct damage by T cells and humoral immunity as well as oxidative stress, glutamate-mediated excitotoxicity, and neuronal and oligodendrocyte apoptosis. Neuroprotective drugs that were once only considered for classical degenerative diseases, such as amyotrophic lateral sclerosis and Parkinson's disease, are now being considered in MS.     

B‐cell–activating factor is elevated in serum of patients with myasthenia gravis

Introduction: Myasthenia gravis (MG) is a B‐cell–mediated autoimmune disease. B‐cell–activating factor (BAFF) is a major factor in B‐cell development and activation. In this study we investigated serum BAFF levels in MG patients. Methods: We compared the serum BAFF levels of 20 MG patients with gender‐matched healthy controls. We assayed serum concentrations of BAFF and anti‐acetylcholine receptor antibody (AChR) titers. Results: Serum BAFF levels of MG patients with AChR antibodies were significantly higher than those of healthy controls. A significant positive correlation was observed between serum BAFF levels and anti‐AChR antibody titers. BAFF values did not correlate with disease severity. Conclusions: BAFF may play a major role in the pathogenesis of MG, and it may provide a potential target for therapy in patients with MG. Muscle Nerve 54 : 1030–1033, 2016     

Is MS an inflammatory or primary degenerative disease?

Multiple sclerosis (MS) is characterized by multiple areas of inflammation, demyelination and neurodegeneration. Multiple molecular and cellular components mediate neuroinflammation in MS. They involve: adhesion molecules, chemokines, cytokines, matalloproteases and the following cells: CD4+ T cells, CD8+ T cells, B cells, microglia and macrophages. Infiltrating Th1 CD4+ T cells secrete proinflammatory cytokines. They stimulate the release of chemokines, expression of adhesion molecules and can be factors that cause damage to the myelin sheath and axons. Chemokines stimulate integrin activation, mediate leukocyte locomotion on endothelial cells and participate in transendothelial migration. CD8+ cells can directly damage axons. B cells are involved in the production of antibodies which can participate in demyelination. B cells can also function as antigen presenting cells and contribute to T cell activation. Neuroinflammation is not only present in relapsing–remitting MS, but also in the secondary and primary progressive forms of the disease. The association between inflammation consisting of T cells, B cells, plasma cells and macrophages and axonal injury exists in MS patients including the progressive forms of the disease. The above association does not exclude the possibility that neurodegeneration can exist independently from inflammation. Very little inflammation is seen in cortical MS plaques. Anti-inflammatory therapies with different mode of action change the course of MS. Anti-inflammatory and immunomodulatory treatments are beneficial in the early relapsing stage of MS, but these treatments are ineffective in secondary progressive and primary progressive MS. In the stage of progressive MS, inflammation becomes trapped behind a closed or repaired blood–brain barrier. In such a situation current immunomodulatory, immunosuppressive or anti-inflammatory treatments might not reach this inflammatory process to exert a beneficial effect.     

Multiple sclerosis: an immune system activation disease.

Two-color flow-cytometric analysis on peripheral blood lymphocytes of 46 untreated multiple sclerosis patients (MS), 36 other medical disease patients (OMD) and 19 healthy control subjects (HC) was performed to know the relationships between T and B cell subpopulations. In MS patients we observed an increase of total lymphocyte count and an increase of CD4+CD29+ cells, which are adjuvant to B cell in antibody production. We hypothesized this change is related to the reduction of CD21+ cells, expressing B2 antigen which disappears after B cell activation. The unperfect balance of immune system in MS was also demonstrated by the increased level of CD25+ cells in relapsing-remitting patients and by the decreased level of CD4+ CD45RA+ (suppressor inducer) cells in progressive patients.     

Opposing effects of CTLA4-Ig and Anti-CD80 (B7-1) plus Anti-CD86 (B7-2) on experimental allergic encephalomyelitis

The roles of the B7 receptors, CD80 and CD86, during actively induced experimental allergic encephalomyelitis were examined with specific monoclonal antibodies and CTLA4-Ig. Injection of CTLA4-Ig on day 2 post-immunization resulted in decreased incidence and severity of resultant disease. Anti-CD80 injection on day 2 blocked development of the first disease episode. Subsequent relapses were unaffected. In contrast, injection of anti-CD86 alone had no effect. Surprisingly, combined anti-CD80 + anti-CD86 monoclonal antibody injection on day 2 resulted in marked exacerbation of disease. Examination of cytokine production in the draining lymph node cells demonstrated a reduction in both interferon (IFN)-γ and interleukin (IL)-2 producing cells, but a dramatic increase in tumor necrosis factor (TNF)-α secretion in animals receiving both monoclonal antibodies. These results suggest distinct roles for CD80 and CD86 in the initiation of EAE, resulting in the diverse clinical outcomes observed in this model of EAE.     

The imbalance in CSF T cell subsets in active multiple sclerosis

We determined the percentage of each lymphocyte subpopulation in the cerebrospinal fluid (CSF) and the peripheral blood of 7 patients with active multiple sclerosis (MS), 7 with inactive MS, 5 with other inflammatory diseases in the central nervous system, and 12 with non-inflammatory neurological diseases, using fluorescein-labelled monoclonal antibodies (anti-Leu7, anti-HLA-DR, and those that recognize such surface antigens as CD3, CD4, CD8, and CD19), and by laser flow cytometry to clarify the clinical usefulness of their measurement in the assessment of disease activity in MS. In CSF, a significant increase in the percentage of CD4+ cells and a significant decrease in the percentage of CD8+ cells were observed in the active MS group compared with the other 3 groups, while none of the percentages of the 6 subsets studied in the peripheral blood were significantly different among these groups. Our preliminary study indicated that evaluation of the percentages of CD4+ and CD8+ cells in CSF by flow cytometry could be a useful indicator of disease activity in MS.