Modification of T- and B-cell-associated immuno-pathologic mechanisms in multiple sclerosis by disease modifying therapies

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS), which can clinically manifest as attacks of neurologic disability and new lesion formation, and a progression of sustained neurologic disability over time. In MS, activated B and T cells are recruited from outside the CNS, and contribute to inflammation, demyelination, and tissue damage inside the brain parenchyma. In the last decades, the treatment of MS has improved by the introduction of several disease-modifying therapies (DMTs). These drugs target generic mechanisms of lymphocyte activation and recruitment or deplete lymphocyte fractions from the circulation. This contributes to a suppression of relapses and new MS lesion formation on MRI. However, the impact on disability progression without relapses is much more variable. In addition, risk mitigation strategies are warranted to control for unwanted side effects of the attenuated immune competence induced by DMTs. In this chapter, we argue that an understanding of the impact of these DMTs on B and T cells both outside and inside the CNS can help to understand the benefits of these therapies but can also help to identify the challenges and opportunities that lie ahead for future MS therapies.