CD20+ T Cells in Multiple Sclerosis: From Pathogenesis to Treatment-Induced Depletion

The traditional paradigm of multiple sclerosis (MS) as a T cell-mediated disorder has been challenged by the effectiveness of monoclonal antibodies (mAbs) targeting CD20- expressing lymphocytes. Although these are mostly represented by B cells, the CD20 marker is expressed by 2–6% of T cells (CD20+ T), which are effectively depleted in serum and cerebrospinal fluid of MS patients by anti-CD20 mAbs. CD20+ T cells are characterized by a pro-inflammatory phenotype and increased potential for migrating and invading the central nervous system (CNS) compared to CD20− T cells. Furthermore, CD20+ T cells are detected within brain inflammatory lesions from MS patients and actively participate in the experimental MS model. This review aims to summarize the current knowledge on CD20+ T cells, from their identification and characterization to evidence of depletion by disease-modifying treatments (DMTs), likely contributing to therapeutic efficacy. Conflicting hypotheses on the origin and development of CD20+ T cells will also be discussed, as well as evidence from clinical and preclinical studies supporting their pathogenetic role in MS.