IL17A and myeloid sarcoma: To reveal early cytokine polarization across these transitional TH cells, we gated on TH cells that responded with IL-2 production to ex vivo reactivation (Extended Data Fig. 5k) and uncovered significantly lower production of IL-9 and higher production of IL-17A and IL-3 in twins with MS than in their unaffected twin sibling (Extended Data Fig. 5l, m).