To identify if baseline blood lymphocyte profile before alemtuzumab treatment initiation could identify patients with an increased risk of developing secondary autoimmunity.

Alemtuzumab is a humanized monoclonal antibody wich has proven to be an effective treatment for patients with highly active multiple sclerosis (MS). However, its use has been limited by frequent adverse events (AEs), specially secondary autoimmunity involving the thyroid gland, observed in about 42% of patients.

Fifty-four RRMS patients, 36 (66.7%) women, with a median (range) age of 28 (13–67) years. Fourteen patients (25.9%) experienced AIAEs, and all of them were dysthyroidism. Patients developing AIAEs had higher percentages of B cells (p=0.001), being differences mainly due to plasmablasts (p=0.003) and naïve cells (p=0.02). By contrast, AIAEs- patients showed a clear increase of the percentages of CD4+ T cells producing TNF-alpha (p=0.019). The ratio between both lymphocyte subsets (B/4TNF) was the best variable to differentiate both groups of patients (p=0.0006). A B/4TNF ratio higher than 0.5 closely associated with higher risk of autoimmune AIAEs (Odds ratio: 52.0, 95% confidence interval: 6.5-565.6, p=2.1x10^-6).

B/4TNF ratio can be a useful tool to stratify the risk of autoimmunity in MS patients who are going to initiate alemtuzumab treatment.