In fact, human in vitro studies have indicated impaired apoptotic deletion of polyclonal and myelin-specific T cells derived from MS patients' blood.34 As the frequency of IL-17-producing cells is higher in MS compared with that in HD,35 we can hypothesise that the impaired apoptotic deletion observed in MS could be related to the higher frequency of cell death resistant compared with sensitive Th subsets in MS. This evidence concerns the gene IL17A and myeloid sarcoma.