title: JCV serology in time: 3 years of follow-up.
abstract: OBJECTIVE
  Although many neurologists are reluctant to use natalizumab in MS (multiple sclerosis) given the increased risk for PML (progressive multifocal leukoencephalopathy), trust was regained with the introduction of JCV antibody titres as a potent disease-modifying therapy. Literature shows that in patients with a negative JCV serology, the risk of PML is virtually non-existent. Unfortunately, seroconversion causes concern amongst many neurologists. Furthermore, when patients seroconvert, it is still unclear what the risk is of passing the important threshold of 1.5.
  
  
  METHODS
  JCV serology data of 161 patients were analysed, upon treatment with natalizumab at the University Hospital in Lille, France, between May 2012 and November 2014.
  
  
  RESULTS
  Of the 81 patients who tested negative for JCV antibody at baseline, 23 (28.3%) seroconverted but only seven (8.6%) passed the threshold of 1.5. Of the 80 patients testing positive for JCV antibody at baseline, eight had an initial JCV antibody titre of 0.9 or lower of which only one of eight (12.5%) patients passed the threshold of 1.5 in the following 3 years. Eight of 15 (53.3%) patients passed this threshold if the initial serology was higher than 0.9.
  
  
  CONCLUSIONS
  JCV-negative patients and JCV-positive patients with antibody levels below or equal to 0.9 both have a low risk of surpassing the 1.5 threshold.
authors.affiliation: CHU Lille, Lille, France.|Universitair Ziekenhuis Brussel, Brussel, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Cambron
authors.affiliation: CHU Lille, Lille, France.
authors.forename: N
authors.initials: N
authors.lastname: Hadhoum
authors.affiliation: CHU Lille, Lille, France.
authors.forename: E
authors.initials: E
authors.lastname: Duhin
authors.affiliation: CHU Lille, Lille, France.
authors.forename: A
authors.initials: A
authors.lastname: Lacour
authors.affiliation: CHU Lille, Lille, France.
authors.forename: A
authors.initials: A
authors.lastname: Chouraki
authors.affiliation: CHU Lille, Lille, France.
authors.forename: P
authors.initials: P
authors.lastname: Vermersch
mesh_terms: D000328:Adult; D000914:Antibodies, Viral / Q000097:blood*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007155:Immunologic Factors / Q000009:adverse effects*; D007577:JC Virus / Q000276:immunology*; D007968:Leukoencephalopathy, Progressive Multifocal / Q000097:blood* / Q000453:epidemiology / Q000209:etiology; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000150:complications / Q000188:drug therapy*; D000069442:Natalizumab / Q000009:adverse effects*; D012698:Serologic Tests
chemical_list: D000914:Antibodies, Viral; D007155:Immunologic Factors; D000069442:Natalizumab
keywords: JCV serology; John Cunningham virus; anti-JCV antibody index; multiple sclerosis; natalizumab; progressive multifocal leukoencephalopathy