Which is the best PML risk stratification strategy in natalizumab-treated patients affected by multiple sclerosis?

Background: The risk of progressive multifocal leukoencephalopathy (PML), a brain infection caused by John Cunningham virus (JCPyV), is the main limitation to the use of natalizumab, highly effective in the treatment of relapsing remitting multiple sclerosis (RRMS) patients. Establishing the PML risk against expected benefits re- presents an obligatory requirement of MS treatment algorithm. In order to achieve this goal, the aims of this study were to establish if JCPyV-DNA detection and non -coding control region (NCCR) arrangements could play a role of biomarkers, supporting anti-JCPyV antibodies measurement, actually the only parameter for PML risk stratification. Methods: Thirty RRMS patients in treatment with natalizumab were enrolled. Urine and blood samples were collected according to this calendar: baseline (T0), 4 (T1), 8 (T2), 12 (T3), 16 (T4), 20 months (T5) after beginning of natalizumab therapy. After JCPyV DNA extraction, a specific quantitative-PCR (Q-PCR) and ar- rangements ? analysis of NCCR and Viral Capsid Protein 1 (VP1) were carried out. Results: Q-PCR detected JCPyV DNA in urine and blood from baseline (T0) to 20 natalizumab infusions (T5), although JC viral load in urine was significantly higher compared to viremia, at all selected time points. A contextual analysis of the anti-JCPyV-antibodies versus JCPyV-DNA detection revealed that viral DNA preceded the antibodies ? presence in the serum. During the first year of natalizumab treatment, sequences isolated from blood displayed an archetype JCPyV NCCR structure with the occurrence of point mutations, whereas after one year NCCR re -organizations were observed in plasma and PBMC with duplication of NF -1 binding site in box F, duplication of box C and partial or total deletion of box D. VP1 analysis showed the amino acid change mutation S269F in plasma and S267L in PBMC, involving the receptor -binding region of VP1. Phylogenetic analysis suggested a stability and a similarity across different isolates of the JCPyV VP1. Conclusions: We highly recommend considering JCPyV-DNA detection and NCCR re -organizations as viral bio- markers in order to accurately identify JCPyV-infected patients with a specific humoral response not yet de- tectable and to identify NCCR arrangements correlated with the onset of neurovirulent variants.