We hypothesize, that in the initial phase of MS–dominated by neuroinflammation–the activation of IDO-1 can be actually beneficial in the short term since it can suppress autoimmune processes via modulation of the T cell mediated immune response (as a negative feedback loop) and promote the development of immune tolerance (Mellor and Munn, 2004; Mancuso et al., 2015). Here, IDO1 is linked to myeloid sarcoma.