Emboldened or not: The potential fall-out of a failed anti-EBV trial in multiple sclerosis

Multiple sclerosis and infection: history, EBV, and the search for mechanism

SUMMARYInfection has long been hypothesized as the cause of multiple sclerosis (MS), and recent evidence for Epstein-Barr virus (EBV) as the trigger of MS is clear and compelling. This clarity contrasts with yet uncertain viral mechanisms and their relation to MS neuroinflammation and demyelination. As long as this disparity persists, it will invigorate virologists, molecular biologists, immunologists, and clinicians to ascertain how EBV potentiates MS onset, and possibly the disease's chronic activity and progression. Such efforts should take advantage of the diverse body of basic and clinical research conducted over nearly two centuries since the first clinical descriptions of MS plaques. Defining the contribution of EBV to the complex and multifactorial pathology of MS will also require suitable experimental models and techniques. Such efforts will broaden our understanding of virus-driven neuroinflammation and specifically inform the development of EBV-targeted therapies for MS management and, ultimately, prevention.

New views on the complex interplay between degeneration and autoimmunity in multiple sclerosis

Multiple sclerosis (MS) is a frequently disabling neurological disorder characterized by symptoms, clinical signs and imaging abnormalities that typically fluctuate over time, affecting any level of the CNS. Prominent lymphocytic inflammation, many genetic susceptibility variants involving immune pathways, as well as potent responses of the neuroinflammatory component to immunomodulating drugs, have led to the natural conclusion that this disease is driven by a primary autoimmune process. In this Hypothesis and Theory article, we discuss emerging data that cast doubt on this assumption. After three decades of therapeutic experience, what has become clear is that potent immune modulators are highly effective at suppressing inflammatory relapses, yet exhibit very limited effects on the later progressive phase of MS. Moreover, neuropathological examination of MS tissue indicates that degeneration, CNS atrophy, and myelin loss are most prominent in the progressive stage, when lymphocytic inflammation paradoxically wanes. Finally, emerging clinical observations such as "progression independent of relapse activity" and "silent progression," now thought to take hold very early in the course, together argue that an underlying "cytodegenerative" process, likely targeting the myelinating unit, may in fact represent the most proximal step in a complex pathophysiological cascade exacerbated by an autoimmune inflammatory overlay. Parallels are drawn with more traditional neurodegenerative disorders, where a progressive proteopathy with prion-like propagation of toxic misfolded species is now known to play a key role. A potentially pivotal contribution of the Epstein-Barr virus and B cells in this process is also discussed.

Targeting Epstein-Barr virus in multiple sclerosis: when and how?

PURPOSE OF REVIEW

Epidemiological evidence implicates Epstein-Barr virus (EBV) as the cause of multiple sclerosis (MS). However, its biological role in the pathogenesis of MS is uncertain. The article provides an overview of the role of EBV in the pathogenesis of MS and makes a case for targeting EBV as a treatment strategy for MS.

RECENT FINDINGS

EBV potentially triggers autoimmunity via molecular mimicry or immune dysregulation. Another hypothesis, supported by immunological and virological data, indicates that active EBV infection via latent-lytic infection cycling within the central nervous system or periphery drives MS disease activity. This supports testing small molecule anti-EBV agents targeting both latent and lytic infection, central nervous system-penetrant B-cell therapies and EBV-targeted immunotherapies in MS. Immunotherapies may include EBV-specific cytotoxic or chimeric antigen receptors T-cells, therapeutic EBV vaccines and immune reconstitution therapies to boost endogenous EBV-targeted cytotoxic T-cell responses.

SUMMARY

EBV is the probable cause of MS and is likely to be driving MS disease activity via latent-lytic infection cycling. There is evidence that all licensed MS disease-modifying therapies target EBV, and there is a compelling case for testing other anti-EBV strategies as potential treatments for MS.