CTLA4 and psoriasis: Due to the mixed mechanism of action of CTLA4-Ig on both costimulatory and co-inhibitory pathways, as well as the greater sensitivity of Th17 to co-inhibition by CTLA-4 [35], several groups evaluated the efficacy of selective CD28 antagonists in the context of skin inflammation (DTH, Transplantation) and, more particularly, psoriasis.