Mechanistically-based Optimization of UV Radiation Therapy in Psoriasis

• Histological response [ Time Frame: Four & 48 hour post drug treatment and one hour post UVB treatment ] [ Designated as safety issue: No ]
  Imiquimod was able to induce an expected gene response (ie MyxA) in psoriatic lesions only in a subset of patients. Imiquimod pretreatment effect on expected Laser UVB effects are still under analysis.
  
  

• Lesional Psoriasis Area and Assessment [ Time Frame: Assessed via the Psoriasis Area and Severity Index at each study visit. ] [ Designated as safety issue: No ]
  No consistent clinical effect.
  
  

The characteristic lesion of psoriasis is a sharply demarcated erythematous papule or plaque with excessive scaling due to hyperproliferating keratinocytes, infiltrating granulocytes, and a dense mononuclear infiltrate with activated T cells. To date, no one mechanism has been explanatory for the panoply of changes that occur in both the dermis and epidermis of psoriasis patients. Several key findings have shown that cutaneous T cells play a key role in the propagation of the disease; memory-type T cells home to the skin, specifically due to expression of cutaneous lymphocyte antigen (CLA), and are the main effector cells in psoriatic tissue responsible for the production of cytokines that result in exacerbated cutaneous inflammation. T cell recruitment is thought to occur in psoriasis, in part, as a result of cytokine and chemokine release from keratinocytes, macrophages, and endothelial cells. CLA-positive T cells migrate into the tissues where memory-effector T cells are activated and expand. This migration is critical to maintenance of the psoriasis lesions, because anti-LFA-1 antibodies (efalizumab) are effective in treating psoriasis, resulting in blood lymphocytosis and tissue depletion of T cells. Despite many years of using UVB phototherapy in the treatment of psoriasis, its mechanism of action is based mainly on in vitro exposures of isolated cells and on extrapolations from UV effects on normal skin, with little direct data from lesional skin.

Previously, our studies determined optimal single efficacious dose using the Excimer laser, refined the mechanism of UVB action in psoriasis, developed key cytokine quantitative meth -ods to assess targeted mRNA levels in psoriatic tissue after treatment, demonstrated that regulatory T cells from psoriasis tissue and blood appear to have a functional defect, and demonstrated that UVA component of solar radiation is a critical and significant contributor to UV-induced in vivo immuno-suppression. All of these previous findings lead us to our current hypothesis that direct selective apoptotic effects on the T mem/Teff cells may result in decreased APC activation and IL-12 over-riding of Treg suppression and a re-balanced Tre:Tmem/eff cell ratio which in turn may have a sustained remittive effect (high duration multi-month clearing of a psoriasis lesion after a single UVB laser light treatment.)