This study aims to characterize longitudinal changes in the clonal compositions of multiple sclerosis (MS) patients’ peripheral lymphocyte repertoires before and during Alemtuzumab treatment, to better understand the beneficial properties and potential side effects of this drug.

The T cell receptor (TCR) repertoire of CD4+ and CD8+ T cells, and expressed immunoglobulin genes (Ig) of naïve and memory B cells, FACS-purified from peripheral blood of 10 patients with MS sampled before and at three timepoints within 24 months after onset of treatment with Alemtuzumab, and controls were analyzed by Next Generation Sequencing (Illumina Miseq).

Longitudinal FACS-analysis data confirmed a strong decrease of CD4+ and CD8+ T lymphocytes after each antibody infusion, while a moderate reduction of memory B cell population was observed. However, an increase of naïve B cell population was noticeable. 

Clonotype tracking data revealed that strongly expanded T cell clones dominate the CD8+ T cell compartment, which majorly persist, with some fluctuations, during treatment. In contrast, the CD4+ compartment consists of many, homogeneously distributed T cell clones of low abundance. Moreover, the memory B cell compartment contains strongly expanded clones, which hardly persist over time. In both T and B lymphocyte populations, Alemtuzumab treatment seems to “reshuffle“ the “Top 100“ clones, including some apparent clonal “losses“, with partial recovery over time.

Results analyzed so far show remarkably characteristic patterns of clonal expansion, clonal abundance and clonal evolution/persistence over time of individual lymphocyte subpopulations, which are differentially affected by Alemtuzumab treatment. Further data analysis and correlation with clinical data is ongoing to better understand which of the observed effects are responsible for maintaining immune competence, a beneficial “remolding’’ of auto-aggressive immune components or the development of secondary autoimmune conditions under Alemtuzumab treatment.