ERVW-1 and myeloid sarcoma: While the HERV-W/MSRV Env expression has been documented in both normal and MS brains, making a pivotal role of these proteins in the disease onset unlikely (Grandi and Tramontano, 2017), their increased presence in MS lesions and their ability to trigger adaptive and, especially, innate immunity suggested that they could take part, with other individual factors, to MS immunopathogenesis (Table 3).