title: Anti-JC virus antibody titres increase over time with natalizumab treatment.
abstract: BACKGROUND
  Anti-JC virus antibody status is a risk factor for progressive multifocal leukoencephalopathy after natalizumab treatment in multiple sclerosis. Previous studies have used a cross-sectional approach to conclude that the presence and duration of natalizumab treatment does not influence anti-JCV Ab seropositivity.
  
  
  OBJECTIVE
  Using a longitudinal approach, we measured change in anti-JCV Ab results after natalizumab treatment.
  
  
  METHODS
  Anti-JCV Ab results (n = 1154) from the second-generation STRATIFY JCV™ DxSelect™ test were analysed from an observational cohort of MS patients on natalizumab (n = 485; n = 340 with repeat testing; n = 657 repeat tests on natalizumab).
  
  
  RESULTS
  Across sequential paired tests, seroconversion rate was greater than seroreversion rate (40/364 (11.0%) versus 18/293 (6.1%); p < 0.05). Moreover, anti-JCV Ab index increased across longitudinal paired tests (mA-B 0.102; paired t(656) = 5.0; p < 0.0001). This magnitude of Ab level increase far exceeds that expected due to increasing age alone.
  
  
  CONCLUSIONS
  Our data suggest that natalizumab therapy is associated with a significant and substantial increase in anti-JCV Ab index over time. Further work should focus on the underlying mechanisms of this phenomenon, and the clinical relevance to risk stratification.
authors.affiliation: Department of Medicine, Imperial College London, UK joelraffel@doctors.org.uk.
authors.forename: J
authors.initials: J
authors.lastname: Raffel
authors.affiliation: Department of Medicine, Imperial College London, UK.
authors.forename: A R
authors.initials: AR
authors.lastname: Gafson
authors.affiliation: Department of Medicine, Imperial College London, UK.
authors.forename: O
authors.initials: O
authors.lastname: Malik
authors.affiliation: Department of Medicine, Imperial College London, UK.
authors.forename: R
authors.initials: R
authors.lastname: Nicholas
mesh_terms: D000328:Adult; D000914:Antibodies, Viral / Q000097:blood*; D005260:Female; D006801:Humans; D007155:Immunologic Factors / Q000009:adverse effects*; D007577:JC Virus / Q000276:immunology*; D007968:Leukoencephalopathy, Progressive Multifocal / Q000097:blood*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000097:blood* / Q000188:drug therapy*; D000069442:Natalizumab / Q000009:adverse effects*
chemical_list: D000914:Antibodies, Viral; D007155:Immunologic Factors; D000069442:Natalizumab
keywords: JC virus; Multiple sclerosis; natalizumab; progressive multifocal leukoencephalopathy