To evaluate the short-term efficacy and safety profile of a sub-group of multiple sclerosis (MS) patients from The University of NSW patient cohort (n=126) who have switched from the anti-CD20 DMTs rituximab and ocrelizumab, to oral cladribine. 

Following administration, oral cladribine (a chlorinated analogue of deoxyadenosine) produces rapid and sustained reductions in CD4+ & CD8+ T cells and rapid, though more transient, effects on CD19+ B cells. Since the pivotal trial of cladribine in RRMS in 2005, there have been significant advances in available disease modifying treatments (DMTs) - in particular targeted therapies that deplete B cells. To our knowledge, the effects of switching from anti-CD 20 DMTs to cladribine on lymphocyte subsets have not yet been evaluated.

Descriptive statistics were used to analyse baseline characteristics at time of cladribine initiation, including patient demographics and reason for switching DMTs. Clinical data were collected on cladribine treatment, duration and management of the washout period between treatments, and relapse or adverse events during washout and after the initiation of cladribine. Overall lymphocytes and subsets were measured at baseline, 3 weeks, 8 weeks and 6 months after starting therapy with cladribine. Expanded Disability Status Scale (EDSS) and MRI scans were captured at 6 monthly intervals over 1 year.

In total, 17 patients with MS switched from anti-CD20 DMTs to cladribine after a mean of 27 weeks (66% female; mean age, 46 years). Mean EDSS score at the initiation of cladribine was 5.5. Almost all patients were switched from ocrelizumab for lack of perceived efficacy. The effect on lymphocytes remained predictable, despite initiating cladribine tablets at or around the lower limit of normal. Reported AEs on cladribine were comparable to those reported in the literature.

Oral cladribine has a predicable effect on lymphopenia when switching from anti-CD20 DMTs.