• To evaluate longitudinal stability of JC virus index over 5 years in a cohort of patients on Natalizumab

John Cunningham (JC) virus status and index level are used to counsel patients on risks of developing PML and are the primary reason for discontinuation of Natalizumab. Given the risks associated with discontinuing Natalizumab, careful evaluation of PML risk is required. Stratification of JCV index has allowed a more accurate representation of risk for patients.  However index levels can vary within individuals.  Despite multiple studies reviewing JC virus stability, the majority have limited follow up describing index values collected over 1-2 years.  Previous studies have shown conflicting evidence as to whether duration of therapy influences stability of JC virus.

In this retrospective real world study, JC virus serology of all patient with MS receiving Natalizumab between 2012 and 2018 were reviewed. Anti JC serology status and index value were determined using STRATIFY JCV Dx Select assay.  

184 patients commenced Natalizumab within the period. 156 patients continued therapy for more than one year and were included in the study. 52 patients had received Natalizumab for > 5 years.  66 patients were negative at baseline and remained negative throughout.  17 patients seroconverted during the period reviewed, giving a seroconversion rate of 4% per year.  13/17 patients who seroconverted had received Natalizumab for > 5 years.  377 index values were available for 80 patients with positive serology.   In patients with more than 4 index values available (n = 58), 35 showed a stable or downward trend, with 23 trending upwards.

This real-world study supports the theory that duration of therapy influences seroconversion.  The majority of patients exhibited stability of JCV index over time. Trend of JC index over time may be a better marker of PML risk than single index.