Method of assessing risk of pml

A method of treating a Multiple Sclerosis (MS) patient, the method comprising acquiring the result of an assay for detecting JC Virus (JCV) antibodies in a biological sample from the patient, and responsive to a determination that the sample is negative for anti-JCV antibodies, administering an anti-VLA-4 therapy, wherein the assay comprises:

• a) forming a first reaction mixture comprising a first aliquot of said sample and a substrate on which is disposed highly purified viral-like particles (HPVLP);
• b) detecting the level of anti-JCV antibody bound to said substrate on which is disposed HPVLP by detecting a labeled detection reagent bound to anti-JCV antibody bound to said substrate, evaluating a cut-off calibrator having a score of about 1, a positive control having a score of about 1.3, and a negative control having a score of about 0.1, and assigning to the sample a value indicative of the level of anti-JCV antibody;
• c) responsive to a level of anti-JCV antibody corresponding to a nOD value between 0.2 and 0.4 in step b), forming a second reaction mixture containing a second aliquot of said sample and solution-phase HPVLP, and detecting the level of unbound antibody in said second reaction mixture, by detecting anti-JCV antibody capable of binding with a substrate on which is disposed HPVLP;
• d) forming a third reaction mixture containing a third aliquot under conditions where anti-JCV antibodies in the sample are not bound by HPVLP or other antigen, and detecting the level of unbound anti-JCV antibody in the third reaction mixture by detecting anti-JCV antibody capable of binding with a substrate on which is disposed HPVLP;
• and
• e) determining the level to which the presence of HPVLP in the second reaction mixture inhibits the level of unbound anti-JCV antibody in said second reaction as compared with the level of unbound antibody in said third reaction mixture, wherein said sample is classified as negative when said inhibition is less than 45%.