Psoriasis vulgaris, a skin disease that is considered to be the result of a type 1 autoimmune response, provides an opportunity for studying the changes that occur in a target-diseased tissue during innovative immunotherapies. To gain a more comprehensive picture of the response to an approved biological therapy, we studied alfacept, which is a CD2 binding fusion protein. We examined T cells, dendritic cells (DCs), and expression of a number of inflammatory genes. In 22 patients, 55% demonstrated a clear histological remission of the disease, with a 73% reduction in lesional lymphocytes and a 79% decrease in infiltrating CD8⁺ cells. Only histological responders showed marked reductions in the tissue expression of inflammatory genes IFN-γ, signal transducer and activator of transcription 1, monokine induced by IFN-γ, inducible NO synthase, IL-8, and IL-23 subunits. Parallel decreases in CD83⁺ and CD11c⁺ DCs also were measured by immunohistochemistry. Because we observed that alefacept binds primarily to T cells and not DCs, we suggest that T cells are the primary target for therapy, but that DCs and a spectrum of type 1 inflammatory genes are coordinately suppressed.