CD8+CD20+ Cytotoxic T Lymphocytes Exhibit Augmented Degranulation and Pro-inflammatory Potential in Multiple Sclerosis

The effectiveness of CD20-targeting therapies in multiple sclerosis (MS) underscores the role of B cells in the disease, yet the limited success of other B cell-specific treatments suggests additional mechanisms at play. Intriguingly, CD20 is also expressed on a subset of highly active memory T cells, particularly cytotoxic CD8+ T lymphocytes (CTLs). This study investigated the functional characteristics of CD8+CD20+ CTLs in MS. We observed a significant increase in CD8+CD20+ CTL prevalence in MS patients, with enhanced infiltration into the cerebrospinal fluid. Consistent with prior reports, these cells exhibited heightened proliferation and production of IFN-{gamma}, TNF-, and GM-CSF. Notably, we demonstrate for the first time that CD8+CD20+ CTLs display escalated degranulation and produce significantly higher levels of Granzyme B, Perforin, and Granzyme K compared to their CD20-counterparts, with further augmentation in pwMS compared to healthy controls. These findings suggest that in MS, CD8+CD20+ CTLs are actively recruited to the CNS, exhibiting enhanced cytotoxicity and a potent pro-inflammatory profile, particularly through elevated Granzyme K production, contributing significantly to the chronic inflammatory milieu and immunopathogenesis of MS.