We hypothesized that preconditioning human umbilical cord blood mesenchymal stem cells (hUCB-MSCs) with the proinflammatory cytokines interleukin 17 (IL-17), IL-22, and tumor necrosis factor alpha (TNF-α), the increased levels of which are typical in psoriasis patients, can significantly increase the therapeutic efficacy of both hUCB-MSCs and their exosomes (hUCB-MSC-Exo). Here, IL17A is linked to psoriasis.