Define the mechanisms underlying the short- and the long-lasting effects of IL-23 targeting in plaque PsO, by characterizing the longitudinal effects of IL-23 inhibition on the ratio of Trm/Treg cells in the skin of moderate to severe plaque PsO patients. HDST (Visium HD) and HDSP (MICS) are used to characterize the early (2 weeks) and late (16 weeks) molecular effects of treatment with tildrakizumab on the skin of three patients with moderate to severe plaque psoriasis. Non-lesional and lesional skin samples taken at the start of treatment with tildrakizumab will be used, as well as healed skin adjacent to the original sampling sites at week 2 and week 16 after the start of treatment with tildrakizumab. The same samples will be examined using Visium HD and the MACSima imaging system.