SignificanceB cell depletion via anti-CD20 monoclonal antibodies is a novel, highly efficient therapy for multiple sclerosis (MS). In a murine MS model, we investigated three mechanistic questions that cannot be addressed in humans. First, we established that a fraction of mature B cells in the spleen is resistant to anti-CD20. Second, we determined that, after cessation of treatment, splenic and bone-marrow B cells reconstitute in parallel, substantially preceding B cell reappearance in blood. Third, we observed that, in a model involving activated B cells, the post–anti-CD20 B cell pool contained an elevated frequency of differentiated, myelin-reactive B cells. Together, our findings reveal mechanisms by which pathogenic B cells may persist in anti-CD20 treatment.
In the pathogenesis of central nervous system (CNS) demyelinating disorders, antigen-specific B cells are implicated to act as potent antigen-presenting cells (APC), eliciting waves of inflammatory CNS infiltration. Here, we provide the first evidence that CNS-reactive antibodies (Ab) are similarly capable of initiating an encephalitogenic immune response by targeting endogenous CNS antigen to otherwise inert myeloid APC. In a transgenic mouse model, constitutive production of Ab against myelin oligodendrocyte glycoprotein (MOG) was sufficient to promote spontaneous experimental autoimmune encephalomyelitis (EAE) in the absence of B cells, when mice endogenously contained MOG-recognizing T cells. Adoptive transfer studies corroborated that anti-MOG Ab triggered activation and expansion of peripheral MOG-specific T cells in an Fc-dependent manner, subsequently causing EAE. To evaluate the underlying mechanism, anti-MOG Ab were added to a co-culture of myeloid APC and MOG-specific T cells. At otherwise undetected concentrations, anti-MOG Ab enabled Fc-mediated APC recognition of intact MOG; internalized, processed and presented MOG activated naïve T cells to differentiate in an encephalitogenic manner. In a series of translational experiments, anti-MOG Ab from two patients with an acute flare of CNS inflammation likewise facilitated detection of human MOG. Jointly, these observations highlight Ab-mediated opsonization of endogenous CNS auto-antigen as a novel disease- and/or relapse-triggering mechanism in CNS demyelinating disorders.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-016-1559-8) contains supplementary material, which is available to authorized users.
Anti-CD20-mediated B-cell depletion effectively reduces acute multiple sclerosis (MS) flares. Recent data shows that antibody-mediated extinction of B cells as a lasting immune suppression, harbors the risk of developing humoral deficiencies over time. Accordingly, more selective, durable and reversible B-cell-directed MS therapies are needed. We here tested inhibition of Bruton’s tyrosine kinase (BTK), an enzyme centrally involved in B-cell receptor signaling, as the most promising approach in this direction. Using mouse models of MS, we determined that evobrutinib, the first BTK inhibiting molecule being developed, dose-dependently inhibited antigen-triggered activation and maturation of B cells as well as their release of pro-inflammatory cytokines. Most importantly, evobrutinib treatment functionally impaired the capacity of B cells to act as antigen-presenting cells for the development of encephalitogenic T cells, resulting in a significantly reduced disease severity in mice. In contrast to anti-CD20, BTK inhibition silenced this key property of B cells in MS without impairing their frequency or functional integrity. In conjunction with a recent phase II trial reporting that evobrutinib is safe and effective in MS, our mechanistic data highlight therapeutic BTK inhibition as a landmark towards selectively interfering with MS-driving B-cell properties.
B cell depletion via anti-CD20 antibodies is a highly effective treatment for multiple sclerosis (MS). However, little is known about the maturation/activation stage of the returning B cell population after treatment cessation and the wider effects on other immune cells. In the present study, 15 relapsing-remitting MS patients receiving 1,000 mg of rituximab were included. B, T, and myeloid cells were analyzed before anti-CD20 administration and in different time intervals thereafter over a period of 24 mo. In comparison to the phenotype before anti-CD20 treatment, the reappearing B cell pool revealed a less mature and more activated phenotype: 1) reappearing B cells were significantly enriched in transitional (before: 10.1 ± 1.9%, after: 58.8 ± 5.2%) and mature naive phenotypes (before: 45.5 ± 3.1%, after: 25.1 ± 3.5%); 2) the frequency of memory B cells was reduced (before: 36.7 ± 3.1%, after: 8.9 ± 1.7%); and 3) reappearing B cells showed an enhanced expression of activation markers CD25 (before: 2.1 ± 0.4%, after: 9.3 ± 2.1%) and CD69 (before: 5.9 ± 1.0%, after: 21.4 ± 3.0%), and expressed significantly higher levels of costimulatory CD40 and CD86. T cells showed 1) a persistent increase in naive (CD4+: before: 11.8 ± 1.3%, after: 18.4 ± 3.4%; CD8+: before: 12.5 ± 1.4%, after: 16.5 ± 2.3%) and 2) a decrease in terminally differentiated subsets (CD4+: before: 47.3 ± 3.2%, after: 34.4 ± 3.7%; CD8+: before: 53.7 ± 2.1%, after: 49.1 ± 2.7%).
Introduction: B cells have increasingly come under the spotlight as mediators of inflammatory central nervous system (CNS) demyelinating diseases such as multiple sclerosis (MS). B cell depletion via the targeting of the surface molecule CD20 has proven to be highly effective; however, continuous absence of an integral component of the immune system may cause safety concerns over time. Declining humoral competence and potential immune system impairments are key issues, and moreover, unselective removal of B cells reduces immune system control functions which should preferably be maintained in inflammatory CNS disease. Areas covered: This paper illuminates the novel approach of specific interference with B cell signaling by targeting Bruton´s tyrosine kinase (BTK). We discuss the role of BTK within the B cell receptor (BCR) signaling cascade and BTK inhibition as a promising strategy to control inflammatory CNS disease which crucially excludes immune-cell depletion. We searched PubMed or clinicaltrials.gov for the terms 'BTK inhibition' or 'Bruton´s Tyrosine Kinase' or 'anti-CD20ʹ and 'Multiple Sclerosis' Expert opinion: BTK inhibition has shown effectiveness in preclinical models of CNS disease and MS clinical trials. Further studies are necessary to differentiate this approach from B cell depletion and to position it in the armamentarium of therapeutics.
Patients with multiple sclerosis are often given vitamin D supplements. However, Häusler, Torke et al. show an unexpected exacerbation of experimental autoimmune encephalomyelitis in mice given high but not moderate doses of supplementary vitamin D. Continuous high-dose vitamin D caused secondary hypercalcaemia, which promoted pro-inflammatory T-cell responses.
The origin and function of CD20 + T cells are poorly understood. Here, we characterized CD20 + T cells in mice and humans and investigated how they are affected by anti-CD20 antibody treatment. We report that murine CD20 + T cells are unable to endogenously express the B cell lineage marker CD20; the development of CD20 + T cells in rodents requires the presence of CD20-expressing B cells. Our results demonstrated that both murine and human T cells acquire CD20 from B cells via trogocytosis while being activated by an antigen-presenting B cell. In patients with multiple sclerosis (MS) and mice with experimental autoimmune encephalomyelitis (EAE), expression of CD20 on T cells is associated with an up-regulation of activation markers, proinflammatory cytokines, and adhesion molecules, suggesting high pathogenic potential. Supporting this hypothesis, CD20 + T cells expand during active EAE in rodents; furthermore, adoptive transfer of CD20 + T cells into EAE-diseased mice worsened histological and clinical severity. Of direct therapeutic relevance, we demonstrate that the exclusive therapeutic elimination of CD20 + T cells effectively ameliorates EAE, independent of B cells. The results support the hypothesis that CD20 + T cells arise upon B cell–T cell interaction and that depletion of CD20 + T cells might contribute to the success of anti-CD20 antibody therapies in MS and other inflammatory disorders.
The exact cause of multiple sclerosis (MS) is unknown; however, it is considered to be an inflammatory disease of the central nervous system (CNS) triggered by a combination of both environmental and genetic factors. Vitamin D deficiency is also discussed as a possible disease-promoting factor in MS, as low vitamin D status is associated with increased formation of CNS lesions, elevated number of relapses and accelerated disease progression. However, it remains unclear whether this association is causal and related and most importantly, whether vitamin D supplementation in MS is of direct therapeutic benefit. Recently, we could show that in a murine model of MS, administration of a moderate vitamin D dose was of clinical benefit, while excessive vitamin D supplementation had a negative effect on disease severity. Of note, disease exacerbation was associated with high-dose vitamin D caused secondary hypercalcemia. Mechanistically dissecting this outcome, we found that hypercalcemia independent of vitamin D similarly triggered activation of disease-perpetuating T cells. These findings caution that vitamin D should be supplemented in a controlled and moderate manner in patients with MS and concomitantly highlight calcium as a novel potential MS risk factor by itself. In this review, we will summarize the current evidence from animal and clinical studies aiming to assess whether vitamin D may be of benefit in patients with MS. Furthermore, we will discuss any possible secondary effects of vitamin D with a particular focus on the role of calcium on immune cells and in the pathogenesis of CNS demyelinating disease.
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