Lymphopenia predicts infectious complications after alemtuzumab therapy in multiple sclerosis: Real-world experience...

Alemtuzumab, a humanized monoclonal anti-CD52 antibody, is an effective therapy for relapsing multiple sclerosis (MS) but is associated with an increased risk of infections. Real-world safety data from tropical and middle-income settings remain limited. We aimed to evaluate infectious complications after alemtuzumab therapy and identify clinical predictors of infection.

We performed a retrospective analysis of a prospectively maintained database of all MS patients receiving a first course of alemtuzumab at the largest public hospital in Brazil between February 2023 and August 2024. Clinical and laboratory data were collected through monthly follow-up.

Forty-four patients received alemtuzumab, and 29 (65.9%) developed at least one infectious episode, totaling 47 events. Most infections were mild, predominantly upper respiratory (33.9%) and urinary tract infections (25.5%). Three hospitalizations occurred, with no deaths. Infection risk increased during periods of lower lymphocyte counts. In a generalized estimating equation model adjusted for follow-up month, lymphocyte counts below 500 cells/μL were associated with higher odds of infection during the corresponding monthly interval (OR 3.69; 95% CI 1.70-7.98; p = 0.0009). Leukocyte and neutrophil counts were not associated with infection occurrence.

In this real-world cohort, infectious events after alemtuzumab were common but mostly mild. Lymphocyte counts below 500 cells/μL identified periods of increased infection risk, supporting intensified clinical and laboratory monitoring during immune depletion.