Abstract The IL-17A/IL-23 pro-inflammatory axis has been established as an influential therapeutic target in psoriasis. However, long-term systemic treatment with IL-17- and IL-23-directed antibody biologics can be immunosuppressive and should be reserved for the more severe disease manifestations. This proposal is focused on the development of topical oligonucleotides targeting IL-17A and IL-23 transcripts. Although topical treatments for plaque psoriasis exist, their efficacy is modest. A highly specific therapy that effectively penetrates plaques for topical treatment of plaque psoriasis continues to be a significant unmet need. Our therapeutic approach is a novel one, based on an "enhancing microRNA" mechanism. We have begun developing an innovative platform of target site blocker (TSB) oligonucleotides that interfere with the enhancing effect of miR466l-3p (miR466) in an individual target mRNA-specific fashion, thereby repressing expression of only that gene. We have successfully generated an IL-17A mRNA-specific TSB that is highly effective in IL-17-dependent murine immune/inflammatory models of multiple sclerosis, autoimmune uveitis, and topically in imiquimod (IMQ)- induced psoriasis. Our hypothesis that IL-17A- and IL-23- directed TSB oligos, formulated for highly penetrable topical use, will synergistically represent a novel, highly specific, RNA-directed treatment in psoriasis. We have assembled an outstanding collaborative team, which includes Dr. Mark Saltzman, an expert in nucleic acid targeting through nanoparticles, and Dr. Jordan Pober, who has developed human-to-mouse skin xenograft models. Our team now proposes to: (1) generate an IL-23- specific TSB oligonucleotide with in vitro and in vivo (IMQ-induced psoriasis) validation, (2) optimize poly(amine-co-ester) (PACE) nanoparticle (NP)-loaded IL-23 and IL-17A TSBs, with testing in vivo (IMQ model), and (3) determine the penetrability of the TSB-loaded NPs into human skin, using human- to-mouse skin xenografting and confocal imaging-based penetration analysis. This molecular, preclinical model and biomedical nanoparticle engineering promises to develop novel therapeutic molecules for topical targeting of the IL-17A/23 axis in plaque psoriasis.