Pointing out one specific inhibitor, the envelope (ENV) protein encoded by the human endogenous retrovirus type W (HERV-W) was previously shown by us to interfere with oligodendroglial cell differentiation (Kremer et al., 2013; Göttle et al., 2019a) contributing to the number of MS-related pathological roles of this factor as summarized previously (Küry et al., 2018). Here, ERVW-1 is linked to myeloid sarcoma.