Anti-JCV antibody index seroconversion in Turkish multiple sclerosis patients treated with natalizumab

The anti-JCV antibody index is widely used to monitor multiple sclerosis (MS) patients receiving natalizumab, as seroconversion is linked to an increased risk of progressive multifocal leukoencephalopathy. This study aimed to evaluate the prevalence and risk factors of anti-JCV antibody seroconversion in patients treated with natalizumab. We included MS patients exposed to natalizumab treatment for at least one year, with a negative anti-JCV antibody index at baseline, and a minimum of two anti-JCV antibody assessments more than six months apart. We employed Kaplan-Meier survival analysis to assess the median time to seroconversion and the annual seroconversion rate, and univariate and multivariate Cox regression models to evaluate the covariates. Among 96 patients followed for a median of 99 months, 29 (30.2%) patients had seroconversion. The median time to seroconversion was 8.3 years, with an annual rate of 6.1%. Seroconversion rates were higher in smokers (p = 0.02) and patients with a body mass index (BMI) over 25 kg/m (p = 0.006). Patients who started natalizumab at age 35 or older had a shorter median time to seroconversion (p = 0.003), and most seroconversions occurred within the first three years. No significant associations were found with gender, prior immunosuppressive treatment, MS subtype, or MS age of onset. Anti-JCV seroconversion is more likely in patients who smoke, have a higher BMI, start natalizumab therapy after age 35, and within the first three years of treatment. For these high-risk patients, vigilant monitoring of anti-JCV antibodies is required.