Dynamics of spinal fluid immune cell alterations following cladribine tablet treatment in multiple sclerosis

Background and ObjectivesOral cladribine tablet (CladT) therapy is efficacious for relapsing multiple sclerosis (MS). However, the mechanisms by which cladribine exerts benefit in MS remain unclear, particularly regarding its effects on compartmentalized inflammation within the cerebrospinal fluid (CSF). MethodsTranscriptional profiles along with T and B lymphocyte receptor repertoires from CSF and blood were obtained by single cell sequencing methods from a single site participating in a phase IV clinical trial investigating the impact of cladribine treatment for MS. All subjects provided blood and CSF samples immediately before starting CladT therapy and were randomized to also provide samples at either five weeks, ten weeks, one year, or two years post-CladT therapy. Thirty-four samples from 13 individuals with relapsing MS before and after treatment were available to test the hypothesis that CladT alters the composition and phenotype of lymphocytes in the CSF. ResultsWe found that treatment with CladT profoundly altered cellular composition, but not the transcriptional phenotype, of immune cells in the CSF. In particular, we identified a reduction of switched memory B cells but recovery of naive B cells in the CSF, similar to our findings in blood. Additionally, populations of CD4 Treg cells emerged early after CladT therapy and remained elevated one year later in the CSF, but not in the blood. Antigen receptor sequencing revealed a moderate decrease in numbers of large clonally expanded CD8 T cell clones (>10 cells/clone) primarily in the CSF, but also in the blood post-CladT treatment. DiscussionOur results identified unique cellular dynamics and changes in T and B cell clonality in both tissues which can potentially explain long-term beneficial effects of CladT therapy in MS, including preservation of immune function and relatively low number of side effects. Altogether, this study demonstrates that CladT treatment had a substantial impact not only on blood, but also on the CSF compartment highlighting the importance of cross-tissue analysis for better understanding of effect and the mechanism of action of DMTs.