Natalizumab effects on immune cell responses in multiple sclerosis

Immunological consequences of ischemic stroke: immunosuppression and autoimmunity

Stroke may be accompanied by immunological consequences including local autoimmunity and peripheral immune suppression. Since the blood brain barrier is disturbed cells of the immune system gain direct access to the brain parenchyma. Here local autoimmunity contributes to lesion formation and, in experimental stroke, inhibition of this immune response has been shown to be beneficial. More recently, however, stroke has been shown to also induce severe peripheral immune suppression which predisposes for subsequent bacterial infections that impair the clinical outcome. Here we summarize current knowledge on the immunological consequences of ischemic stroke and will discuss implications of these findings for our understanding of the immunopathogenesis of Multiple Sclerosis.

Adhesion molecules are promising candidates to establish surrogate markers for natalizumab treatment

BACKGROUND

Natalizumab is the first monoclonal antibody therapy approved for multiple sclerosis (MS). Its therapeutic mechanism is the blockade of the α4-integrin subunit of the adhesion molecule (AM) very late activation antigen-4 (VLA-4), which leads to an inhibition of immune cell extravasation into the central nervous system (CNS).

METHODS

We investigated changes in the expression levels of unblocked α4-integrin and further AM (intercellular adhesion molecule-1, -2, -3 (cICAM-1, -2, -3), leukocyte function associated antigen-1 (LFA-1)) on peripheral blood mononuclear cells (PBMC) determined by flow cytometry from 25 patients with MS before the first natalizumab infusion and before the fourth infusion. In 15 MS patients AM expression was evaluated every 3 months over 1 year.

RESULTS

We found a significant decrease (p < 0.0001) of unblocked α4-integrin cell surface expression on all investigated PBMC subsets (T cells -61.7%, B cells -69.1%, monocytes/macrophages -46.4%) in the blood of MS patients after 3 months of natalizumab treatment. Moreover, a continuous decrease (p < 0.05) of unblocked α4-integrin expression levels was seen after 3, 6, 9, and 12 months. As a secondary effect, expression levels of the other investigated AM were differentially affected.

CONCLUSIONS

Results show a sustained decrease of unblocked α4-integrin expression not only in all patients but also in all investigated PBMC subsets. This probably results in a continuously decreasing transmigration of PBMC into the CNS and may explain the improved clinical efficacy in the second treatment year and also the increasing risk of progressive multifocal leukoencephalopathy during long-term natalizumab therapy. We conclude that AM expression profiles are promising candidates for the development of a biomarker system to determine both natalizumab treatment response and patients at risk for opportunistic CNS infections.

Translational research in neurology and neuroscience 2010: multiple sclerosis

Over the past 2 decades, enormous progress has been made with regard to pharmacotherapies for patients with multiple sclerosis. There is perhaps no other subspecialty in neurology in which more agents have been approved that substantially alter the clinical course of a disabling disorder. Many of the pharmaceuticals that are currently approved, in clinical trials, or in preclinical development were initially evaluated in an animal model of multiple sclerosis, experimental autoimmune encephalomyelitis. Two Food and Drug Administration-approved agents (glatiramer acetate and natalizumab) were developed using the experimental autoimmune encephalomyelitis model. This model has served clinician-scientists for many decades to enable understanding the inflammatory cascade that underlies clinical disease activity and disease surrogate markers detected in patients.

Update on the treatment options for multiple sclerosis

Recent progress in the treatment of multiple sclerosis (MS) is remarkable, and the introduction of new therapies is yielding improvements in the management of MS. Furthermore, clinical trials with many different types of agents, especially selected monoclonal antibodies, have been undertaken or are ongoing, and some of the agents involved will probably be available as treatments for MS in the near future. Although these new and promising agents include targeted immunotherapies, some of them have limitations such as associated severe adverse events and the development of neutralizing antibodies. With regard to risk-benefit ratios, pharmacogenetics could shed light on inherited differences in drug metabolism and response, which would make individualized therapy possible in MS. Here, we review the recent progress in current therapeutic strategies for MS, and the potential options for future MS treatment.

Natalizumab treatment in multiple sclerosis: marked decline of chemokines and cytokines in cerebrospinal fluid

Natalizumab exerts impressive therapeutic effects in patients with multiple sclerosis (MS). The proposed main mode of action is reducing transmigration of leukocytes into the CNS, but other immunological effects may also be operative. Cytokines and chemokines are involved in the regulation of inflammatory responses and may reflect the disease process in MS. The objective of this study was to evaluate the effects of natalizumab treatment on cytokine and chemokine profiles systemically and intrathecally in multiple sclerosis. We used luminex to analyse a panel of cytokines (IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, TNF-alpha, IFN-gamma, GM-CSF) and chemokines (CXCL9, CXCL10, CXCL11, CCL17, CCL22) in blood and cerebrospinal fluid (CSF) from 31 patients with relapsing MS before and after one year of natalizumab treatment. There was a marked decline in CSF levels of cytokines and chemokines, thus including pro-inflammatory cytokines (IL-1beta, IL-6 and IL-8) as well as chemokines associated with both Th1 (CXCL9, CXCL10, CXCL11) and Th2 (CCL22). Circulating plasma levels of some cytokines (GM-CSF, TNF-alpha, IL-6 and IL-10) also decreased after one year of treatment. This is the first study to show that natalizumab treatment is associated with a global decline in cytokine and chemokine levels at a protein level. This finding was most pronounced in CSF, in line with the reduced transmigration of cells into CNS, whereas reduction in plasma levels indicates other possible mechanisms of natalizumab treatment.

Restoring immune suppression in the multiple sclerosis brain

Multiple sclerosis is a very disabling inflammatory demyelinating disease of the brain of unknown etiology. Current therapies can reduce new lesion development and partially prevent clinical disease activity, but none can halt the progression, or cure the disease. We will review current therapeutic strategies, which are mostly discussed in literature in terms of their effective inhibition of T cells. However, we argue that many of these treatments also influence the myeloid compartment. Interestingly, recent evidence indicates that myelin phagocytosis by infiltrated macrophages and activated microglia is not just a hallmark of multiple sclerosis, but also a key determinant of lesion development and disease progression. We reason that severe side effects and/or insufficient effectiveness of current treatments necessitates the search for novel therapeutic targets, and postulate that these should aim at manipulation of the activation and phagocytic capacity of macrophages and microglia. We will discuss three candidate targets with high potential, namely the complement receptor 3, CD47-SIRPalpha interaction as well as CD200-CD200R interaction. Blocking the actions of complement receptor 3 could inhibit myelin phagocytosis, as well as migration of myeloid cells into the brain. CD47 and CD200 are known to inhibit macrophage/microglia activation through binding to their receptors SIRPalpha and CD200R, expressed on phagocytes. Triggering these receptors may thus dampen the inflammatory response. Our recent findings indicate that the CD200-CD200R interaction is the most specific and hence probably best-suited target to suppress excessive macrophage and microglia activation, and restore immune suppression in the brain of patients with multiple sclerosis.

Memory and naïve B-cell subsets in patients with multiple sclerosis

Memory and naïve B cells are considered to play distinct roles in immune regulation. However, the roles of memory and naïve B-cell subsets in multiple sclerosis (MS) have not yet been elucidated. In this study, we examined whether memory and naïve B-cell subsets differ between patients with MS and healthy subjects and whether interferon beta (IFNbeta)-1b can affect these subsets in patients with MS. We also studied these subsets in relapsing and remitting stages of MS. Subjects included 31 patients with relapsing-remitting MS in the remitting stage, of which 15 were treated with IFNbeta-1b and 16 were not treated, and 22 healthy control subjects. For 11 of the 16 untreated patients, blood samples were also obtained in the relapsing stage. Expression of CD5, CD80, CD86, CCR5, CXCR3, CD11a, and CD49d in memory and naïve B cells in blood samples was examined by flow cytometry. The percentages of CD86(+) cells and CCR5(+) cells in the naïve B-cell subset were significantly higher in untreated patients than in control subjects or IFNbeta-treated patients. In patients with MS, the percentages of CD86(+) cells and CCR5(+) cells in the naïve B-cell subset and the percentage of CD5(+) cells in the memory B-cell subset were significantly greater in the remitting stage than in the relapsing stage. These results indicate that memory and naïve B-cell subsets, especially CD86(+) naïve B cells, CCR5(+) naïve B cells, and CD5(+) memory B cells, might be useful in the study of the pathogenesis of and therapy for MS.

Natalizumab treatment is associated with peripheral sequestration of proinflammatory T cells

BACKGROUND

Natalizumab is an antibody directed against integrin alpha4 that reduces disease activity in patients with multiple sclerosis (MS) by blocking migration of T and B cells into the CNS. The goal of this study was to characterize the effects of natalizumab treatment on cytokine production and expression of activation markers, costimulatory molecules, and trafficking determinants on CD4+ and CD8+ T cells.

METHODS

In a longitudinal study, we investigated the expression of surface makers and cytokine expression on peripheral blood lymphocytes from 28 patients with MS who started natalizumab treatment and were followed for 1 year. A mixed effects model was used to compare pretreatment to on-treatment measurements.

RESULTS

The frequency of CD4+ T cells producing interferon-gamma, tumor necrosis factor, and interleukin (IL)-17 upon anti-CD3 stimulation increased 6 months after initiation of natalizumab treatment and remained elevated throughout the follow-up. The frequency of CD4+ T cells expressing CD25, HLA-DR, and CCR6 ex vivo was increased at one or more time points during treatment. Among CD8+ T cells, the frequency of cells producing IL-2 and IL-17 after stimulation was increased during natalizumab treatment, as was the frequency of CD8+ T cells expressing CD58 and CCR5 ex vivo. The increase in the frequency of activated cells could not be replicated by in vitro exposure to natalizumab.

CONCLUSION

Natalizumab treatment increases the percentage of activated leukocytes producing proinflammatory cytokines in blood, presumably due to sequestration of activated cells in the peripheral circulation.

The effects of natalizumab on inflammatory mediators in multiple sclerosis: prospects for treatment-sensitive biomarkers

BACKGROUND

Natalizumab affects systemic cytokine expressions and clinical course in relapsing-remitting multiple sclerosis (RRMS). We analyzed levels of inflammatory cytokines in cerebrospinal fluid (CSF) cells and peripheral blood mononuclear cells (PBMCs), levels of matrix metalloproteinase (MMP)-9 and osteopontin (OPN) in CSF, and clinical outcome measures in 22 natalizumab-treated RRMS patients.

METHODS

mRNA levels of cytokines in cells were detected with real-time RT-PCR. Protein levels of OPN and MMP-9 were measured by ELISA.

RESULTS

Natalizumab reduced CSF cell counts (P < 0.0001). Tumor necrosis factor (TNF) and interferon-gamma (IFN-gamma) mRNAs were significantly increased in PBMCs. In contrast, expressions of IFN-gamma and interleukin (IL)-23 were decreased but IL-10 increased in the CSF cells. OPN and MMP-9 were reduced in the CSF. Patients being in remission at baseline showed the same deviations of mediators as those in relapse after natalizumab treatment. The open label clinical outcome measures were either stable or improved during therapy.

CONCLUSIONS

Natalizumab attenuates pro-inflammatory mediators intrathecally and the reduced pro-inflammatory milieu may allow increased production of the anti-inflammatory mediator IL-10. The increased systemic cytokines may impede the improvement of certain clinical measures like fatigue. The affected mediators seem to be sensitive to an immune-modifying treatment which could be used as biomarkers for this therapy.

The binding specificity and selective antagonism of vedolizumab, an anti-alpha4beta7 integrin therapeutic antibody in development for inflammatory bowel diseases

Vedolizumab is a humanized monoclonal antibody that targets the alpha(4)beta(7) integrin exclusively, and modulates inflammation in the gastrointestinal tract without inducing the systemic immunosuppression that characterizes anti-alpha(4) chain monoclonal antibodies, such as natalizumab. This unique pharmacologic profile is largely attributable to four determinants. The first determinant is the restriction of the expression of the alpha(4)beta(7) integrin to subsets of leukocytes. Vedolizumab does not bind to the majority of memory CD4(+) T lymphocytes (60%), neutrophils, and most monocytes. The highest level of vedolizumab binding is to a subset (approximately 25%) of human peripheral blood memory CD4(+) T lymphocytes that include gut-homing interleukin 17 T-helper lymphocytes. Vedolizumab also binds to eosinophils at high levels, and to naive T-helper lymphocytes, naive and memory cytotoxic T lymphocytes, B lymphocytes, natural killer cells, and basophils at lower levels; vedolizumab binds to memory CD4(+) T and B lymphocytes with subnanomolar potency (EC(50) = 0.3-0.4 nM). The second determinant is binding specificity; vedolizumab binds exclusively to the alpha(4)beta(7) integrin, and not to the alpha(4)beta(1) and alpha(E)beta(7) integrins. The third determinant is selective antagonism; vedolizumab selectively inhibits adhesion of alpha(4)beta(7)-expressing cells to mucosal addressin cell adhesion molecule 1 (median inhibition concentration [IC(50)] = 0.02-0.06 microg/ml) and fibronectin (IC(50) = 0.02 microg/ml), but not vascular cell adhesion molecule 1. The fourth determinant is the gastrointestinal-specific tropism of the alpha(4)beta(7) integrin function. These pharmacologic properties of vedolizumab, in conjunction with the gastrointestinal tropism of alpha(4)beta(7) integrin function, may ultimately confer an improved risk-to-benefit profile for patients with inflammatory bowel diseases.

GLANCE: results of a phase 2, randomized, double-blind, placebo-controlled study

OBJECTIVE

To evaluate the safety and tolerability of natalizumab when added to glatiramer acetate (GA) in patients with relapsing multiple sclerosis. The primary outcome assessed whether this combination would increase the rate of development of new active lesions on cranial MRI scans vs GA alone.

METHODS

This phase 2, randomized, double-blind, placebo-controlled study included patients aged 19 to 55 years who were treated with GA for at least 1 year before randomization and experienced at least one relapse during the previous year. Patients received IV natalizumab 300 mg (n = 55) or placebo (n = 55) once every 4 weeks plus GA 20 mg subcutaneously once daily for < or = 20 weeks.

RESULTS

The mean rate of development of new active lesions was 0.03 with combination therapy vs 0.11 with GA alone (p = 0.031). Combination therapy resulted in lower mean numbers of new gadolinium-enhancing lesions (0.6 vs 2.3 for GA alone, p = 0.020) and new/newly enlarging T2-hyperintense lesions (0.5 vs 1.3, p = 0.029). The incidence of infection and infusion reactions was similar in both groups; no hypersensitivity reactions were observed. One serious adverse event occurred with combination therapy (elective hip surgery). With the exception of an increase in anti-natalizumab antibodies with combination therapy, laboratory data were consistent with previous clinical studies of natalizumab alone.

CONCLUSION

The combination of natalizumab and glatiramer acetate seemed safe and well tolerated during 6 months of therapy.

Natalizumab in the treatment of multiple sclerosis

Natalizumab reduced the rate of clinical relapse at one year by 68% and the risk of sustained progression of disability by 42-54% over 2 years in its pivotal phase III trial (AFFIRM) in relapsing-remitting multiple sclerosis (RRMS). Natalizumab is generally well tolerated, but due to rare and potentially fatal side-effects, it was approved with a restricted-distribution format in 2006. Expert statements and the European Medical Agency recommend the use of natalizumab after failure of first-line disease-modifying therapies in patients with relapsing forms of MS. As part of the risk management plan, worldwide extensive safety programmes aim to provide more data on natalizumab safety in clinical practice. At the end of September 2008, 48 000 patients have received natalizumab and 18000 patients are on treatment for at least 1 year. The assessment of risk and benefit is still ongoing.

Omega-3 fatty acid supplementation decreases matrix metalloproteinase-9 production in relapsing-remitting multiple sclerosis

OBJECTIVES

The primary objective was to evaluate the effect of omega-3 fatty acids (omega-3 FA) on matrix metalloproteinase-9 (MMP-9) production by immune cells in multiple sclerosis (MS). Quality of life, fatty acid levels, and safety were also evaluated.

MATERIALS AND METHODS

Ten participants with relapsing-remitting MS (RRMS) received omega-3 FA supplementation (9.6g/day fish oil) in an open-label study. Participants were evaluated at four time points, baseline, after 1 month of omega-3 FA supplementation, after 3 months of omega-3 FA supplementation, and after a 3-month wash out.

RESULTS

Immune cell secretion of MMP-9 decreased by 58% after 3 months of omega-3 FA supplementation when compared with baseline levels (p<0.01). This effect was coupled with a significant increase in omega-3 FA levels in red blood cell membranes.

CONCLUSIONS

Omega-3 FA significantly decreased MMP-9 levels in RRMS and may act as an immune-modulator that has potential therapeutic benefit in MS patients.

Novel therapeutic strategies for multiple sclerosis--a multifaceted adversary

Therapeutic strategies for multiple sclerosis have radically changed in the past 15 years. Five regulatory-approved immunomodulatory agents are reasonably effective in the treatment of relapsing-remitting multiple sclerosis, and appear to delay the time to progression to disabling stages. Inhibiting disease progression remains the central challenge for the development of improved therapies. As understanding of the immunopathogenesis of multiple sclerosis has advanced, a number of novel potential therapeutics have been identified, and are discussed here. It has also become apparent that traditional views of multiple sclerosis simply as a CD4+ T-cell-mediated disease of the central nervous system are incomplete. The pathogenic role of other immune components such as the innate immune system, regulatory T cells, T helper 17 cells and B cells is reaching centre stage, opening up exciting avenues and novel potential targets to affect the natural course of multiple sclerosis.

The differential amino acid requirement within osteopontin in alpha4 and alpha9 integrin-mediated cell binding and migration

Osteopontin (OPN) contains at least two major integrin recognition domains, Arg159-Gly-Asp161 (RGD) and Ser162-Val-Val-Tyr-Gly-Leu-Arg168 (SVVYGLR), recognized by alphavbeta3 and alpha5beta1 and alpha4 and alpha9 integrins, respectively. OPN is specifically cleaved by thrombin and matrix metalloproteinase (MMP)-3 or MMP-7 at a position of Arg168/Ser169 (R/S) and Gly166/Leu167 (G/L), respectively. We in this study examined the requirement of residues within SVVYGLR for the alpha4 and alpha9 integrin recognition and how MMP-cleavage influences the integrin recognition. The residues, Val164, Tyr165, and Leu167 are critical for alpha4 and alpha9 integrin recognition in both cell adhesion and cell migration. The residue Arg168 is additionally required for alpha9 integrin recognition in cell adhesion and this explains why alpha9 integrin binds to only thrombin cleaved form of OPN. alpha4 integrin is able to bind to SVVYG (MMP-cleaved form of RAA OPN-N half), while alpha9 integrin is not, supporting the above notion that Arg168 is additionally required for alpha9 integrin-mediated cell adhesion. The residue Val163 is important for alpha4, but not for alpha9 integrin recognition in cell migration. Importantly, we found that the replacement of Arg168 by Ala (R168A mutant) induces the augmentation of cell migration via alpha4 and alpha9 integrins.

Effects of natalizumab treatment on Foxp3+ T regulatory cells

Background

Natalizumab, a monoclonal humanized antibody targeting the alpha-4 chain of very late activation antigen 4 (VLA-4) exerts impressive therapeutic effects in patients with relapsing-remitting multiple sclerosis. Our objective was to study impacts of Natalizumab therapy on Foxp3+ T regulatory cells (Tregs) in multiple sclerosis (MS) patients.

Methodology

A combined approach of in vitro and ex vivo experiments using T cells isolated from the peripheral blood of healthy donors and Natalizumab treated MS patients was chosen. We determined binding of Natalizumab and its effects on the frequency, transmigratory behaviour and suppressive function of Tregs.

Principal Findings

Binding of Natalizumab and expression of CD49d (alpha-4 chain of VLA-4) differed between non-regulatory and regulatory cells. Albeit Foxp3+ Tregs had lower levels of CD49d, Natalizumab blocked the transmigration of Foxp3+ Tregs similar to non-regulatory T cells. The frequency of peripheral blood Tregs was unaffected by Natalizumab treatment. Natalizumab does not alter the suppressive capacity of CD4+CD25^highCD127^lowFoxp3+ Tregs under in vitro conditions. Furthermore, the impaired function of Tregs in MS patients is not restored by Natalizumab treatment.

Conclusions

We provide a first detailed analysis of Natalizumab effects on the regulatory T cell population. Our prospective study shows that Foxp3+ Tregs express lower levels of VLA-4 and bind less Natalizumab. We further the understanding of the mechanisms of action of Natalizumab by demonstrating that unlike other immunomodulatory drugs the beneficial therapeutic effects of the monoclonal antibody are largely independent of alterations in Treg frequency or function.

B cells and multiple sclerosis

Clonal expansion of B cells and the production of oligoclonal IgG in the brain and cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS) have long been interpreted as circumstantial evidence of the immune-mediated pathogenesis of the disease and suggest a possible infectious cause. Extensive work on intrathecally produced antibodies has not yet clarified whether they are pathogenetically relevant. Irrespective of antibody specificity, however, the processes of antibody synthesis in the CNS of patients with MS are becoming increasingly clear. Likewise, targeting B cells might be therapeutically relevant in MS and other autoimmune diseases that are deemed to be driven predominantly by T cells. Accumulating evidence indicates that in MS, similar to rheumatoid arthritis, B cells aggregate into lymphoid-like structures in the target organ. The process of aggregation is mediated through the expression of lymphoid-homing chemokines. In the brain of a patient with MS, ectopic B-cell follicles preferentially adjoin the pial membrane within the subarachnoid space. Recent findings indicate that substantial numbers of B cells that are infected with Epstein-Barr virus (EBV) accumulate in these intrameningeal follicles and in white matter lesions and are probably the target of a cytotoxic immune response. These findings, which await confirmation, could be an explanation for the continuous B-cell and T-cell activation in MS, but leave open concerns about the possible pathogenicity of autoantibodies. Going beyond the antimyelin-antibody dogma, the above data warrant further work on various B-cell-related mechanisms, including investigation of B-cell effector and regulatory functions, definition of the consistency of CNS colonisation by Epstein-Barr virus-infected B cells, and understanding of the mechanisms that underlie the formation and persistence of tertiary lymphoid tissues in patients with MS and other chronic autoimmune diseases (ectopic follicle syndromes). This work will stimulate new and unconventional ways of reasoning about MS pathogenesis.

Central nervous system effects of current and emerging multiple sclerosis-directed immuno-therapies

OBJECTIVE

To review the direct and indirect effects on the central nervous system (CNS) of systemically administered immuno-modulatory therapies in use or under evaluation for the relapsing forms of multiple sclerosis (MS).

METHODS

We summarize data published by our own lab and by others that delineate the effects of such therapies on in vitro neural cell cultures and in animal model-based systems.

RESULTS

The long-approved therapies, interferon beta (IFNbeta) and glatiramer acetate (GA), do not readily access the CNS. These agents can still indirectly have an effect on disease-related immune regulatory and effector functions within the CNS by modulating the properties of systemic immune cells that migrate to this compartment. Such immune cells could interact with perivascular and innate immune cells that are involved in immune regulation and with cells that are either targets of the disease process (oligodendrocytes, neurons) and/or are involved with repair (progenitor cells). Newer agents reported to favorably impact on relapse frequency in MS include the sphingosine-1-phosphate agonist, fingolimod, and the lipophilic statin, simvastatin. Both agents access the CNS and thus represent examples of agents that could directly impact on disease-relevant injury and repair process within the CNS.

CONCLUSIONS

The observations reviewed in this report regarding indirect and direct effects of immuno-modulatory agents on the CNS indicate the need to understand and monitor the neurobiologic effects of such therapies.

The effects of natalizumab on the innate and adaptive immune system in the central nervous system

Multiple sclerosis (MS) is an inflammatory demyelinating disorder of the central nervous system (CNS). Natalizumab ((R)Tysabri) is a humanized recombinant monoclonal antibody that binds to the alpha (alpha)(4) chain of the alpha(4) beta (beta)(1) integrin (very late activation antigen 4; VLA-4), and alpha(4)beta(7) integrin. Recently, two patients with MS and one patient with Crohn's disease who were treated with natalizumab in the setting of clinical trials developed progressive multifocal leukoencephalopathy (PML), an opportunistic infection of the brain with the polyoma virus JC. We recently showed that natalizumab decreases the numbers of CD4(+) and CD8(+) T lymphocytes, CD19(+) B cells, and CD138(+) plasma cells in the cerebrospinal fluid (CSF) of patients with MS on natalizumab therapy. In addition, we demonstrated that the cell numbers in CSF remained unchanged even 6 months after cessation of natalizumab treatment.

Treating multiple sclerosis with monoclonal antibodies

Therapeutic monoclonal antibodies (mAbs) are potent new tools for a molecular targeted approach to modify the course of multiple sclerosis (MS). Besides natalizumab, which was approved in 2006, three other mAbs (alemtuzumab, rituximab and daclizumab) were successfully tested in Phase II MS trials. In this review, introductory notes on the development and systematic nomenclature of therapeutic mAbs in general, set the stage for a detailed discussion of the four mAbs mentioned. We summarize non-MS indications, expression and function of target antigens, scientific rationales for MS therapy, putative modes of action and pharmacological aspects. Particularly, we provide a critical discussion of clinical MS trials, including protocols and interim analyses of trials currently underway. The natalizumab section pays special attention to the clinical handling of safety issues and the diagnostic use of neutralizing antibodies. We finally develop a scenario for how each of the four mAbs might evolve into the market of MS therapeutics within the coming years.

MRI of monocyte infiltration in an animal model of neuroinflammation using SPIO-labeled monocytes or free USPIO

Magnetic resonance imaging (MRI) has been applied to visualize monocyte infiltration with the use of intravenously injected ultrasmall superparamagnetic iron oxide (USPIO). However, USPIO uptake in vivo remains elusive, and the heterogeneous enhancement patterns observed by MRI point to multiple pathophysiological events. This study focused on specific imaging of monocyte infiltration into the brain by transfusion of superparamagnetic iron oxide (SPIO)-labeled monocytes in a rat model of neuroinflammation, experimentally induced photothrombosis (PT). At day 5 after lesion induction, animals were transfused with SPIO-labeled monocytes (5 x 10(6) cells) or free USPIO (17 mg Fe/kg). MRI was performed 24, 72 and, 120 h later. To investigate temporal changes directly after intravenous USPIO administration, MRI was performed repeatedly up to 8 h. Relaxation measurements showed that rat monocytes were efficiently labeled in vitro using SPIO (R2=12+/-0.9 s(-1)). After transfusion of SPIO-labeled monocytes, a significant increase in contrast enhanced area (340%+/-106%) in the PT lesion was observed not before 72 h. Contrast enhancement after USPIO injection increased up to 407%+/-39% at a much earlier point of time (24 h) and diminished thereafter. Repetitive MRI directly after USPIO injection showed significant contrast enhancement in the lesion within 2 h. Our study shows that MRI enables in vivo tracking of SPIO-labeled monocytes longitudinally. Moreover, our data suggest that contrast enhancement after injection of free USPIO does not primarily represent signals from peripherally labeled monocytes that migrated toward the inflammatory lesion. The use of SPIO-labeled monocytes provides a better tool to specifically assess the time window of monocyte infiltration.

The immunological basis for treatment of multiple sclerosis

During the last few years, the concept of multiple sclerosis (MS) as a pure inflammatory disease mediated by myelin reactive T cells has been challenged. Neither the specificity nor the mechanisms triggering or perpetuating the immune response are understood. Genetic studies have so far not identified therapeutic targets outside the HLA complex, but epidemiological and immunological studies have suggested putative pathogenetic factors which may be important in therapy or prevention, including the Epstein-Barr virus and vitamin D. Advances in the treatment of MS have been reached by manipulating the immune response where the pathogenesis of MS intersects experimental autoimmune encephalomyelitis, most recently by blocking T-cell migration through the blood-brain barrier. Antigen-specific approaches are effective in experimental models driven by a focused immune response against defined autoantigens, but MS may not fit into this concept. Novel candidate autoantigens which are not constitutively expressed in the brain, such as protein alpha-B crystallin or IgG V-region idiotopes, as well as evidence of pathogenetic heterogeneity and complexity, suggest that treating MS by tolerizing the immune system against an universal MS antigen may be a fata morgana. Further characterization of MS subtypes may lead to individualized treatment. However, shared immunological features, such as intrathecal production of oligoclonal IgG, suggest that potential therapeutic targets may be shared by most MS patients.

Emerging therapies for multiple sclerosis

This review examines the mode of action, safety profile and clinical efficacy of some of the most promising new therapeutic strategies for multiple sclerosis. Autologous hematopoietic stem cell transplantation can regenerate a new and tolerant immune system and is a potentially effective rescue therapy in a subset of patients with aggressive forms of MS refractory to approved immunomodulatory and immunosuppressive agents. High-dose cyclophosphamide without stem cell support is suggested to induce prolonged remissions through similar immunological mechanisms with less toxicity. Fingolimod (FTY720) is a novel oral immunomodulating agent that acts through preventing lymphocyte recirculation from lymphoid organs. Monoclonal antibody therapy has provided scientists and clinicians the opportunity to rationally direct the therapeutic intervention against specific molecules. Targeting molecules of the immune system such as CD52 (alemtuzumab), CD25 (daclizumab), VLA-4 (natalizumab) and CD20 (rituximab) have resulted in potent immunomodulatory effects through sometimes unpredicted mechanisms. The potential of immunoglobulins to induce remyelination in the CNS is being investigated in an attempt to develop therapies promoting tissue repair and functional recovery. The evidence supporting the potential of these emerging immunotherapies suggests that strong progress is being made in the development of effective cures for multiple sclerosis.

Pharmacological properties, toxicology and scientific rationale for the use of natalizumab (Tysabri) in inflammatory diseases

Natalizumab (Tysabri) was the first adhesion molecule antagonist to make it into clinical trial for patients with multiple sclerosis (MS) and other inflammatory disorders. Natalizumab is a humanized recombinant monoclonal antibody (MAb) that binds to the alpha (alpha)(4) chain of the alpha(4) beta (beta)(1) (very late activating antigen 4; VLA-4) and alpha(4)beta(7) integrins. The scientific rationale for natalizumab therapy is the reduction of leukocyte extravasation into peripheral tissues. Natalizumab, like other VLA-4 antagonists, may also interfere with the activation of T lymphocytes in secondary lymphoid organs and their reactivation in the central nervous system (CNS). Shortly after its approval for the treatment of relapsing-remitting MS (RR-MS), three patients who were treated with natalizumab in the setting of clinical trials developed progressive multifocal leukoencephalopathy (PML), an opportunistic infection of the brain with the polyoma virus JC. It remains to be elucidated why the use of this VLA-4 antagonist is associated with an increased incidence of PML. Natalizumab was recently reapproved for the treatment of relapsing forms of MS. In this review, we outline the scientific rationale for using natalizumab in MS and other inflammatory disorders. In addition, an overview of pharmacological properties, clinical efficacy, safety, and toxicology of natalizumab is provided.

Saliva soluble HLA as a potential marker of response to interferon-beta 1a in multiple sclerosis: a preliminary study

Objective

Potential surrogate markers of disease activity, including response to therapy, are particularly important in a neurological disorder such as multiple sclerosis (MS) which often has a fluctuating course. Based upon previous studies in our laboratory, we hypothesized that measurement of soluble HLA (sHLA) molecules class II in saliva of MS patients can serve as marker of therapeutic response to high dose interferon beta-1a.

Methods

We measured the expression patterns of sHLA-II in saliva in 17 patients with relapsing/remitting MS and compared the results to clinical course and brain MRI. For comparison purposes we also assayed the saliva sHLA-II levels in 53 normal control subjects. Solid phase ELISA was used for measurement of sHLA-I and sHLA-II concentrations at baseline and after three and six months of treatment with high dose interferon beta-1a (IFN β-1a).

Results

The mean saliva sHLA-ll levels in MS patients was significantly higher than normal controls (354 ± 42 unit/mL vs. 222 ± 18 unit/mL, t= 8.16, p < 0.003). Comparison of saliva sHLA-II values before and after treatment with IFN β-1a revealed a consistent increase in mean concentration. The increase in saliva sHLA-II values (354 ± 42 unit/mL at baseline versus 821 ± 86 unit/mL at 3 months and 776 ± 63 unit/mL at 6 months, in unit/mL, p < 0.001 for both comparisons) was associated with a stable clinical course and a decline of the number of contrast-enhancing lesions on brain MRI. Comparison of the volume of T2-weighted lesions and the number of black holes on T1-weighted images did not reveal any significant changes (during pre-treatment versus post-treatment month 6) or any correlations with saliva sHLA-II levels. Saliva sHLA-I levels were not detectable.

Conclusion

Serial measurement of saliva sHLA-II may serve as a potential marker of therapeutic response to IFN β-1a. Larger clinical studies involving more RRMS patients over longer periods of time are needed to further test the significance and value of saliva sHLA-II as an accurate marker of therapeutic response to beta-interferons.

B cells: no longer the nondominant arm of multiple sclerosis

The role B cells and humoral immunity play in multiple sclerosis (MS) is continually evolving. Recent discoveries include advances in lesion classification, identification of B cell clonal expansion in the central nervous system with evidence of antigen targeting, identification of chemokines in MS lesions, and expansion of information on the roles of autoantibodies and complement. Strong indications are accumulating that a greater degree of humoral dysfunction may lead to worsened long-term prognosis in MS. Effects of established MS treatments on B cells and their products have been further defined. Treatments that specifically target B cells are being implemented and hold promise.

The blood-brain-barrier in multiple sclerosis: functional roles and therapeutic targeting

In most regions of the central nervous system (CNS), the composition of the neuronal microenvironment is maintained by virtue of particular blood-brain-barrier (BBB) characteristics, to which vascular endothelial cells (ECs) contribute an important role. Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS, characterized at tissue level by multifocal perivascular infiltrates, predominantly of lymphocytes and macrophages. Thus, lymphocyte recruitment into the brain across ECs of the BBB represents a critical event in disease pathogenesis, which is highly restricted and carefully regulated. In recent years, different investigations have identified the crucial components involved in leukocyte migration, providing new insights into mechanisms modulating neuroinflammatory reactions. In this review, several topics relating to these events are discussed, namely: (1) cellular and molecular characteristics of the BBB regulating permeability, as well as signals inducing EC differentiation in the brain and specific cell properties; (2) pathogenic mechanisms guiding the migration of different leukocyte populations through the BBB in MS; and (3) current knowledge on how different MS therapies targeting leukocytes migration across the BBB function. Furthermore, because the BBB has proven to be an important retaining wall preventing drug passage into the CNS, novel strategies directed at successful delivery of large molecules for effective treatment of various inflammatory conditions of the brain, both currently available or still under development, are discussed.

[Update on pathophysiologic and immunotherapeutic approaches for the treatment of multiple sclerosis]

Multiple sclerosis (MS) is a chronic disabling disease with significant implications for patients and society. The individual disease course is difficult to predict due to the heterogeneity of clinical presentation and of radiologic and pathologic findings. Although its etiology still remains unknown, the last decade has brought considerable understanding of the underlying pathophysiology of MS. In addition to its acceptance as a prototypic inflammatory autoimmune disorder, recent data reveal the importance of primary and secondary neurodegenerative mechanisms such as oligodendrocyte death, axonal loss, and ion channel dysfunction. The deepened understanding of its immunopathogenesis and the limited effectiveness of currently approved disease-modifying therapies have led to a tremendous number of trials investigating potential new drugs. Emerging treatments take into account the different immunopathological mechanisms and strategies, to protect against axonal damage and promote remyelination. This review provides a compilation of novel immunotherapeutic strategies and recently uncovered aspects of known immunotherapeutic agents. The pathogenetic rationale of these novel drugs for the treatment of MS and accompanying preclinical and clinical data are highlighted.

Treatment and treatment trials in multiple sclerosis

PURPOSE OF REVIEW

This review focuses on advances in current and novel treatment approaches in multiple sclerosis.

RECENT FINDINGS

New therapeutic approaches in multiple sclerosis are emerging. Orally available treatment strategies are more acceptable for patients and may improve adherence to therapy. An oral formulation of glatiramer acetate failed to demonstrate efficacy in a clinical trial, but other promising compounds are on the horizon, such as FTY720. Advances are currently being made in use of therapeutic monoclonal antibodies that specifically target key molecules involved in the immunopathogenesis of multiple sclerosis. Natalizumab directed against the adhesion molecule very late antigen-4 represents the first specific antibody to be added to our therapeutic armamentarium for multiple sclerosis. Further evidence that immunomodulation should be initiated as early as possible has been reported.

SUMMARY

Treatment of multiple sclerosis has changed dramatically over the past decade. Enhanced understanding of the immunopathological processes that underlie the disease, advances in biotechnology and development of powerful magnetic resonance imaging technologies, together with improvements in clinical trial design have led to a variety of valuable therapeutic approaches, which are currently being studied in detail.

Natalizumab: A new treatment for relapsing remitting multiple sclerosis

Natalizumab, a new disease-modifying therapy for relapsing remitting multiple sclerosis (RRMS), is a humanized monoclonal antibody which binds to alpha(4)beta(1)-integrin. In a Phase 3 trial, 2 years of natalizumab monotherapy reduced the mean annualized relapse rate (ARR) by 68% compared with placebo (p < 0.001) and the risk of sustained disability progression was reduced by 42% in the natalizumab group (hazard ratio [HR] 0.58; 95% confidence interval [CI] 0.43-0.77; p < 0.001). Natalizumab decreased the mean number of new or enlarging T2-hyperintense lesions by 83% over 2 years and the mean number of Gd+ lesions by 92% at 2 years (both p < 0.001). In another Phase 3 trial, natalizumab with interferon (IFN) beta-1a reduced the mean ARR by 55% at 2 years compared with IFNbeta-1a alone (p < 0.001) and risk of sustained disability progression was reduced by 24% (HR 0.76; 95% CI 0.61-0.96; p = 0.02). Six percent of patients developed persistent antinatalizumab antibodies with loss of efficacy. The risk of developing progressive multifocal leukoencephalopathy (PML) is been estimated at 1:1000 over 18 months; the longer term risk for PML is uncertain. The benefits and risks of natalizumab support its use as monotherapy for RRMS with high disease activity despite treatment with IFNbeta, and for patients with rapidly evolving severe RRMS.

Compared benefit of approved and experimental immunosuppressive therapeutic approaches in multiple sclerosis

An important amount has been learnt about the mechanisms of action, efficacy and long-term toxicities of mitoxantrone. Importantly, recent observations strongly suggest that early administration of potent immunosuppressants (mitoxantrone and alemtuzumab) is definitely more effective than approved immunomodulators to delay or even reverse disability progression. Given the cardiotoxicity of mitoxantrone, restricting exposure to the drug to 2 or 3 years, the benefits and risks of immunosuppressants previously used as off-label treatments (cyclophosphamide and cladribine) have been revisited, and the potential efficacy in multiple sclerosis of recent immunosuppressants used in other autoimmune diseases, organ transplantation and cancer therapy has received increasing attention. Those immunosuppressants comprise monoclonal antibodies targeting B cells, lymphocytes and monocytes, IL-2 receptor and alpha4 integrin, as well as new molecules (pixantrone and isoxazole derivatives) and a new generation of immunosuppressants (fingolimod), which modulate lymphocyte re-circulation. This review addresses the most recent data concerning the efficacy and safety of mitoxantrone and of new experimental therapies that are presently in progress.

VCAM-1 activation of endothelial cell protein tyrosine phosphatase 1B

Lymphocytes migrate from the blood into tissue by binding to and migrating across endothelial cells. One of the endothelial cell adhesion molecules that mediate lymphocyte binding is VCAM-1. We have reported that binding to VCAM-1 activates endothelial cell NADPH oxidase for the generation of reactive oxygen species (ROS). The ROS oxidize and stimulate an increase in protein kinase C (PKC)alpha activity. Furthermore, these signals are required for VCAM-1-dependent lymphocyte migration. In this report, we identify a role for protein tyrosine phosphatase 1B (PTP1B) in the VCAM-1 signaling pathway. In primary cultures of endothelial cells and endothelial cell lines, Ab cross-linking of VCAM-1 stimulated an increase in serine phosphorylation of PTP1B, the active form of PTP1B. Ab cross-linking of VCAM-1 also increased activity of PTP1B. This activation of PTP1B was downstream of NADPH oxidase and PKCalpha in the VCAM-1 signaling pathway as determined with pharmacological inhibitors and antisense approaches. In addition, during VCAM-1 signaling, ROS did not oxidize endothelial cell PTP1B. Instead PTP1B was activated by serine phosphorylation. Importantly, inhibition of PTP1B activity blocked VCAM-1-dependent lymphocyte migration across endothelial cells. In summary, VCAM-1 activates endothelial cell NADPH oxidase to generate ROS, resulting in oxidative activation of PKCalpha and then serine phosphorylation of PTP1B. This PTP1B activity is necessary for VCAM-1-dependent transendothelial lymphocyte migration. These data show, for the first time, a function for PTP1B in VCAM-1-dependent lymphocyte migration.

Natalizumab treatment for multiple sclerosis: recommendations for patient selection and monitoring

Natalizumab is a new treatment option for patients with active relapsing-remitting multiple sclerosis. In phase III studies, natalizumab was highly effective and well tolerated; however, three cases of progressive multifocal leucoencephalopathy (PML) were identified (estimated incidence of one per 1000; 95% CI 0.2-2.8; mean treatment period 17.9 months). In this Review we summarise the current information on PML, the three confirmed cases of PML, and the results of an extensive safety assessment of all patients treated with natalizumab. On the basis of these reviews, we make recommendations for appropriate selection of candidates for natalizumab and pretreatment assessments. In addition, a three-step diagnostic and management algorithm was developed to monitor natalizumab-treated patients with multiple sclerosis for PML and other opportunistic infections. The algorithm includes strategies for clinical, MRI, and laboratory assessments. Maintaining clinical vigilance allows for early suspension of natalizumab in potential cases of PML, thereby increasing the opportunity for immune reconstitution, which may improve prognosis if PML is confirmed.

Immune responses to BK and JC viruses in immunocompromised patients

BK virus (BKV) and JC virus (JCV) are ubiquitous human polyomaviruses that establish persistent asymptomatic infections in immunocompetent individuals, but in a minority of immunocompromised patients, reactivate and cause clinical disease. BKV is associated with BKV nephropathy (BKVN) in kidney transplant recipients and JCV is the etiologic agent of progressive multifocal leukoencephalopathy (PML) in AIDS patients. Humoral responses do not appear adequate to protect against reactivation or disease, and both BKVN and PML appear to be due to a failure of cellular immune responses to control the virus. Among the goals of current research is the identification of the functional correlates of cellular immune protection against these viruses in immunocompetent individuals. Such insights may help identify the small subset of patients at risk of BKV and JCV reactivation, aid clinical management and permit the development of immunotherapeutic approaches.

Frequency and phenotype of JC virus-specific CD8+ T lymphocytes in the peripheral blood of patients with progressive multifocal leukoencephalopathy

JC virus (JCV)-specific CD8+ cytotoxic T lymphocytes (CTL) are associated with a favorable outcome in patients with progressive multifocal leukoencephalopathy (PML) and cross-recognize the polyomavirus BK virus (BKV). We sought to determine the frequency and phenotype in fresh blood of CD8+ T cells specific for two A*0201-restricted JCV epitopes, VP1(p36) and VP1(p100), and assess their impact on JC and BK viremia and viruria in 15 healthy subjects, eight human immunodeficiency virus-positive (HIV+) individuals, and nine HIV+ patients with PML (HIV+ PML patients) classified as survivors. After magnetic pre-enrichment of CD8+ T cells, epitope-specific cells ranged from 0.001% to 0.022% [corrected] by tetramer staining, with no significant difference among the three study groups. By use of seven-color flow cytometry, there was no predominant differentiation phenotype subset among JCV-specific CD8+ T cells in healthy individuals, HIV+ subjects, or HIV+ PML patients. However, in one HIV+ PML patient studied in the acute phase, there was a majority of activated effector memory cells. BKV DNA was undetectable in all blood samples by quantitative PCR, while a low JC viral load was found in the blood of only one HIV+ and two HIV+ PML patients. JCV and BKV DNA were detected in 33.3% and 13.3% of all urine samples, respectively, independent of the presence of JCV-specific CTL. The detection of JCV DNA in the urine was associated with the presence of a JCV VP1(p100) CTL response. Immunotherapies aiming at increasing the cellular immune response against JCV may be valuable in the treatment of HIV+ individuals with PML.

New insights into adaptive immunity in chronic neuroinflammation

Understanding the immune response in the central nervous system (CNS) is crucial for the development of new therapeutic concepts in chronic neuroinflammation, which differs considerably from other autoimmune diseases. Special immunologic properties of inflammatory processes in the CNS, which is often referred to as an immune privileged site, imply distinct features of CNS autoimmune disease in terms of disease initiation, perpetuation, and therapeutic accessibility. Furthermore, the CNS is a stress-sensitive organ with a low capacity for self-renewal and is highly prone to bystander damage caused by CNS inflammation. This leads to neuronal degeneration that contributes considerably to the phenotype of the disease. In this chapter, we discuss recent findings emphasizing the predominant role of the adaptive immune system in the pathogenesis of chronic neuroinflammation, that is, multiple sclerosis (MS) in patients and experimental autoimmune encephalomyelitis (EAE) in rodents. In addition, we report on efforts to translate these findings into clinical practice with the aim of developing selective treatment regimens.

VCAM-1 signals activate endothelial cell protein kinase Calpha via oxidation

Lymphocyte binding to VCAM-1 activates endothelial cell NADPH oxidase, resulting in the generation of 1 muM H(2)O(2). This is required for VCAM-1-dependent lymphocyte migration. In this study, we identified a role for protein kinase Calpha (PKCalpha) in VCAM-1 signal transduction in human and mouse endothelial cells. VCAM-1-dependent spleen cell migration under 2 dynes/cm(2) laminar flow was blocked by pretreatment of endothelial cells with dominant-negative PKCalpha or the PKCalpha inhibitors, Rö-32-0432 or Gö-6976. Phosphorylation of PKCalpha(Thr638), an autophosphorylation site indicating enzyme activity, was increased by Ab cross-linking of VCAM-1 on endothelial cells or by the exogenous addition of 1 muM H(2)O(2). The anti-VCAM-1-stimulated phosphorylation of PKCalpha(Thr638) was blocked by scavenging of H(2)O(2) and by inhibition of NADPH oxidase. Furthermore, anti-VCAM-1 signaling induced the oxidation of endothelial cell PKCalpha. Oxidized PKCalpha is a transiently active form of PKCalpha that is diacylglycerol independent. This oxidation was blocked by inhibition of NADPH oxidase. In summary, VCAM-1 activation of endothelial cell NADPH oxidase induces transient PKCalpha activation that is necessary for VCAM-1-dependent transendothelial cell migration.

Chemokines, mononuclear cells and the nervous system: heaven (or hell) is in the details

Chemokines and their receptors are essential elements in leukocyte trafficking during health and disease. There are three (or more) distinct routes of leukocyte entry into the central nervous system (CNS), and molecular mechanisms of physiological and neuroinflammatory leukocyte recruitment to the CNS are slowly coming into view. Migration of immune cells into cerebrospinal fluid supports CNS immunosurveillance. Current knowledge of the trafficking determinants that direct the leukocyte recruitment in CNS pathology relies in large part on studies of multiple sclerosis and its models including experimental autoimmune encephalomyelitis. Overlapping molecular signals are responsible for the migration of specific cells into the CNS during pathological inflammation and host defense, raising challenges and opportunities for therapeutic manipulation.

Alemtuzumab and natalizumab: the monoclonal antibody story continues

In the July/August 2006 issue of this journal, the infectious complications associated with the use of infliximab, etanercept and adalimumab were reviewed (1). These represent only three of the many monoclonal antibodies either licensed or in clinical trials for therapeutic use in cancer and autoimmune disease or to prevent rejection in both solid organ and hematopoietic stem cell transplantation. While most of these agents have not been associated with increased infection rates, alemtuzumab and natalizumab have gained particular attention related to either the frequency or type of infection seen in some individuals who have received them.

Review of Progressive Multifocal Leukoencephalopathy and Natalizumab

BACKGROUND

Progressive multifocal leukoencephalopathy (PML), a destructive demyelinating infection which lytically infects oligodendrocytes, has occurred in patients treated with natalizumab. Magnetic resonance imaging (MRI) scan imaging of the brain gives clues to diagnosis but is nonspecific in distinguishing multiple sclerosis from PML. Spinal fluid detection of JC virus is specific but incompletely sensitive. Associated immunosuppression is typically of the cell-mediated type but can be poorly defined on clinical grounds.

REVIEW SUMMARY

It is apparent that natalizumab is a predisposing factor for developing PML from the 3 cases of natalizumab-treated patients. There is no reliable presymptomatic way to detect PML or JC virus infection of the brain by virologic or imaging surveillance techniques. One patient with multiple sclerosis and natalizumab treatment has survived, indicating that withdrawal of antibody, possibly in combination with antiviral therapy, may permit survival. However, immune reconstitution disease is a risk after immune restoration and withdrawal of natalizumab. PML deficits would be expected to be permanent. The estimate of incidence of PML in natalizumab-treated patients is 1 per 1000. The duration of natalizumab treatment may be an independent risk factor for development of PML.

CONCLUSION

PML, a usually fatal neurologic infection, should be considered as a risk factor when using natalizumab. The treatment of multiple sclerosis patients with natalizumab is a matter of informed risk, individualized for each multiple sclerosis patient.

Roles of immunoglobulins and B cells in multiple sclerosis: from pathogenesis to treatment

Immunoglobulins (Igs) have long been implicated in contributing to the disease course of multiple sclerosis (MS). The earliest and perhaps still most consistent abnormal immunologic laboratory finding in MS is the increased concentration of Ig in the CSF, representing intrathecal antibody synthesis. Analysis of CSF Ig in terms of rate of production and restricted diversity (oligoclonal bands) remains a supportive diagnostic criteria for MS. Despite large-scale studies such as the analysis of 1000 cases reported by Ebers and Paty [Ebers, G.C., Paty, D.W., 1980. CSF electrophoresis in one thousand patients. Can. J. Neurol. Sci. 7 (4) 275-280], the challenge of correlating CSF Ig profiles and specific disease phenotypes remains. More recently, evidence from animal models and several human studies suggests that antibody-independent functions of B cells may also be implicated in the pathogenesis of MS. This presentation considers what roles Ig and/or B cells can play in mediating or regulating disease-relevant immune responses in MS. A timely corollary is whether B cell/Ig-directed therapeutic strategies can be effective in MS.

Progressive multifocal leukoencephalopathy revisited: Has the disease outgrown its name?

Nothing is more disappointing for patients than when a promising new treatment hits a roadblock because of unexpected side effects. This is what happened when natalizumab (Tysabri) was associated with a few cases of progressive multifocal leukoencephalopathy (PML) in multiple sclerosis and Crohn's disease patients, caused by the reactivation of the polyomavirus JC. These dramatic events drew PML squarely into the spotlight and generated considerable interest from the medical community, the pharmaceutical industry, financial markets, and regulatory agencies alike. This scrutiny, in turn, helped crystallize areas of consensus and expose gaps in our understanding of PML pathogenesis. Indeed, since its initial description, there has been a considerable evolution in both the epidemiology and clinical presentations of this disease, and new manifestations of central nervous system infection by polyomavirus JC have been characterized. To keep pace with this opportunistic pathogen, we are therefore forced to reexamine the foundations of our knowledge of virus-host interactions, reappraise our investigational approaches, and in short, rethink PML down to its very name. Hopefully, this crisis will be instrumental in helping us define novel avenues of research, develop predictive tests for PML in populations at risk, and challenge us to find a treatment for this deadly disease.