Unfortunately, treatments with biologicals are increasingly associated with amplified susceptibility to viral infections, in particular, new studies are performed to understand the role of Polyomavirus John Cunningham (JCPyV) in development of a demyelinating disease, named Progressive Multifocal Leukoencephalopathy (PML), in patients treated with anti-TNF α (Comar et al., 2013). This evidence concerns the gene TNF and progressive multifocal leukoencephalopathy.