RAPID COMMUNICATION Anti-JC Virus Antibodies: Implications for PML Risk Stratification Leonid Gorelik, PhD, 1 Michaela Lerner, MS, 1 Sarah Bixler, MPhil, 1 Mary Crossman, MS, 1 Brian Schlain, MS, 1 Kenneth Simon, PhD, 1 Amy Pace, ScD, 1 Anne Cheung, MS, 1 Ling Ling Chen, MS, 1 Melissa Berman, MS, 1 Fairuz Zein, MSc, 1 Ewa Wilson, MS, 1 Ted Yednock, PhD, 2 Alfred Sandrock, MD, PhD, 1 Susan E. Goelz, PhD, 1 and Meena Subramanyam, PhD 1 Objective: A study was undertaken to establish an enzyme-linked immunosorbent assay (ELISA) to detect JC virus (JCV)-specific antibodies in multiple sclerosis (MS) patients, and to evaluate its potential utility for identifying patients at higher or lower risk (ie, risk stratification) of developing progressive multifocal leukoencephalopathy (PML). Methods: A 2-step assay for detecting and confirming the presence of anti-JCV antibodies in human serum and plasma was developed and demonstrated to be both sensitive and specific. ELISA cutpoints were statistically established using sera from >800 MS patients from natalizumab clinical studies. Subsequently, this assay was used to determine the presence of anti-JCV antibodies in natalizumab-treated PML patients where serum samples were collected 16-180 months prior to the diagnosis of PML. Results: In our evaluation of natalizumab-treated MS patients, 53.6% tested positive for anti-JCV antibodies, with a 95% confidence interval of 49.9 to 57.3%. The false-negative rate of the ELISA was calculated to be approximately 2.5%, with an upper 1-sided confidence limit of 4.4%. Notably, we observed anti-JCV antibodies in all 17 available pre-PML sera samples, which was significantly different from the 53.6% seropositivity observed in the overall MS study population (p < 0.0001). Interpretation: This 2-step assay provides a means to classify MS patients as having detectable or not detectable levels of anti-JCV antibodies. The finding that all 17 of the pre-PML samples that were available tested seropositive, and none tested seronegative, warrants further research on the clinical utility of the anti-JCV antibody assay as a potential tool for stratifying MS patients for higher or lower risk of developing PML. ANN NEUROL 2010;68:295–303 P rogressive multifocal leukoencephalopathy (PML) is a rare brain disease caused by the JC virus (JCV), a common polyomavirus. 1 Primary infection by JCV typi- cally occurs in childhood or adolescence, and the benign form of JCV may remain asymptomatic in the kidneys 2,3 and possibly the lymphoid organs throughout life. Through complex, poorly understood interactions between host and viral factors, 4 JCV undergoes altera- tions in the regulatory region 5 and mutations in the coat protein VP1 6 to cause a lytic infection of myelin-produc- ing oligodendrocytes, leading to development of PML. PML generally occurs in severely immune-compromised individuals, as well as in some patients receiving certain immunosuppressive (mycophenolate mofetil) 7 or biologic (eg, efalizumab, natalizumab, alemtuzumab, rituximab) 4,8 therapies. Identification of patients at lower or higher risk for developing PML may allow more appropriate use of vari- ous therapies. Because infection by JCV is a prerequisite for PML development, serologic detection of anti-JCV antibodies may prove to be a sensitive means to deter- mine current or past infection with JCV. Anti-JCV sero- positivity rates between 33 and 91%, have been previ- ously reported. This discrepancy in rates is likely due to differences in sample size, demographics, and perhaps most importantly, assay methodologies. 9–20 In this report, View this article online at wileyonlinelibrary.com. DOI: 10.1002/ana.22128 Received Mar 4, 2010, and in revised form Jun 16, 2010. Accepted for publication Jun 16, 2010. Address correspondence to Dr Subramanyam, 14 Cambridge Center, Cambridge, MA 02142. E-mail: meena.subramanyam@biogenidec.com From 1 Biogen Idec, Inc., Cambridge MA; 2 Elan Corporation, South San Francisco CA. Additional Supporting Information can be found in the online version of this article. V C 2010 American Neurological Association 295