Oral Cladribine B-cell Study

Primary: To quantify the temporal changes of memory B cells (CD19+/CD27+/IgD-/+), plasmablasts (CD19-/CD138+/CD38+) and T cells (CD4/CD45RA-/+, CCR7-/+, CD8+/CD45RA-/+/CCR7-/+), Tregs (CD4/CD8)/CD25+/CD127-/Fox3 P+) in the peripheral venous blood of pwMS with RRMS over 96w of treatment with oral cladribine. These will be compared to the populations of non-memory or class-switched B cells (immature/transitional B cells CD10+/CD38+/CD19+, immature regulatory B cells CD10+/CD38+/CD19+/CD24+/IL-10+, mature B cells CD10-/CD38+/CD19+). Secondary: 1. To study the effects of oral cladribine on: 1. CSF OCBs and free immunoglobulin kappa and lambda light chain levels (FLC). 2. CSF markers of inflammation, in particular CXCL-13 and urine markers of inflammation (neopterin). 3. CSF markers of neuroaxonal damage, in particular free neurofilament light chains. 4. On the peripheral repertoire B-cells (immunoglobulin) and T-cells (T cell receptor) and plasma cells (soluble receptors). 2. To compare CSF OCB positivity and CSF light chain levels with a contemporary control group of alemtuzumab treated pwMS (historical data). Tertiary: 1. To compare B and T cell repertoire with a contemporary control group of alemtuzumab treated pwMS (historical data). 2. To evaluate the effect of changes in the immune cell profile on clinical measures of disability, MRI activity and PROMS.