Risk of infection and immunosuppression in relapsing–remitting multiple sclerosis treated with alemtuzumab: A 3.5-year follow-up study

Introduction: Alemtuzumab has demonstrated efficacy and safety in clinical trials for relapsing–remitting multiple sclerosis (RRMS). However, real-world patients do not always meet the strict inclusion criteria of clinical trials, making it essential to assess outcomes in clinical practice. The objective of this study is to describe the risk of infections and immunosuppression in patients with RRMS treated with alemtuzumab, over a 42-month follow-up period. Methods : We conducted a retrospective, open-label, multicentre study. Inclusion criteria were: patients diagnosed with RRMS who received alemtuzumab between 2015 and 2024. The primary endpoint of the study was to evaluate the incidence of infections reported in patient medical records. The risk of immunosuppression was assessed through lymphocyte count in blood during the first month after each treatment cycle and then every 3 months until the end of follow-up. Results: A total of 32 patients were included. Urinary tract infections and herpes infections were the most common, generally without complications. Regarding the risk of immunosuppression, severe lymphocytopenia occurred only during the first month following each treatment cycle. Subsequently, lymphocyte counts progressively increased. No significant correlation was found between lymphocyte levels and infection risk. Conclusions: Alemtuzumab has demonstrated a favourable safety profile with regard to the risk of infections, maintaining a controlled risk of immunosuppression, which can be managed with an effective detection and treatment protocol.