Background: Relapsing-remitting multiple sclerosis (RRMS) is an autoimmune inflammatory disorder of the central nervous system, with significant morbidity and mortality. The lymphocyte depleting, anti-CD52 monoclonal antibody alemtuzumab is a highly effective treatment option in RRMS, though associated with high rates of secondary autoimmune disorders. As alemtuzumab is now in routine clinical use, following licensing in Europe and the US, understanding the effects of repeated treatment cycles and reducing the risk of secondary autoimmunity is timely and essential. In this thesis, I explore how repeated treatment impacts the extent of lymphodepletion. I also study the role of soluble CD52, recently described as suppressive via interaction with Siglec-10, in the mechanism of secondary autoimmunity, and determine the biomarker potential of pre-treatment cytokine levels.

Findings: CD4 and CD8 lymphocytes are less effectively depleted with repeated treatment cycles. Lymphocyte surface CD52 density was found by flow cytometry to be significantly lower after alemtuzumab treatment, although CD52-negative clones are not seen. In a cytolysis assay, reduced CD52 density was shown to correlate with reduced susceptibility to alemtuzumab. In addition, activated proliferating T lymphocytes, as observed after treatment, downregulated CD52 expression in a gene expression assay and shed the antigen from cell surface as demonstrated by ELISA and flow cytometry. The development of immunoassays to detect and quantify anti-idiotype antibodies to alemtuzumab is presented. The occurrence of antibodies at retreatment did not reduce lymphocyte depletion.

A regulatory role for soluble CD52 was not found in suppression assays, and the proportion of antigen-activated CD52hi T cells did not vary between healthy controls and RRMS individuals. Siglec-10 was not seen on cell surface of activated T cells by flow cytometry and gene expression; thus concluding that soluble CD52 does not play a role in post-alemtuzumab induced autoimmunity.

Prior to treatment, the only serum cytokine found to distinguish individuals who develop autoimmunity from those who do not was IL-21 (higher in the autoimmune cohort), however currently commercially available IL-21 immunoassays have no utility as predictive biomarker tests.