Ultraviolet (UV) light is part of normal sunlight and has many effects on human skin and health. One of the harmful effects of long-term UV light exposure is that it can cause skin cancer. The mechanism by which UV light causes skin cancer is not entirely understood. One of the ways UV light causes cancer is by modifying DNA molecules in the cells of the skin. Another mechanism involved in cancer formation by UV light is immunosuppression. By this mechanism, UV light inactivates cells of the immune system of the skin. The immune cells are responsible for the detection and destruction of foreign substances and organisms such as bacterias and viruses but they also recognize and destroy cancer cells. UV light is known to prevent cells of the immune system to destroy cancer cells. In laboratory experiments, a medication called denosumab has been shown to diminish the inhibition of ultraviolet-induced suppression of skin immunity. In other words, this medication could block the effect of UV on cells of the immune system and might allow patients taking this drug to be better protected from skin cancer. The objective of this study is to test whether denosumab blocks the immunosuppressive effect of UVB light in healthy subjects. This study is divided into two stages. In the first stage, ten subjects (Cohort 1) will be sensitized to diphenylcyclopropenone (DPCP), a topical sensitizer commonly used for the treatment of alopecia areata and cutaneous warts. By reexposing the subjects to DPCP in incremental doses, dose-response levels of cutaneous hypersensitivity reactions in normal skin will be obtained. This will allow comparison of the normal levels of DPCP-induced cutaneous hypersensitivity (CHS) reaction in non UV-exposed skin (Cohort 1) to the CHS obtained from the two UVB-exposed experimental groups of Cohort 2. In the second stage of the study, 20 subjects (Cohort 2) will be exposed to an immunosuppressive dose of ultraviolet B (UVB) 24 hours prior to DPCP sensitization. This is expected to result in the abolition of CHS upon rechallenge with DPCP. In order to assess whether denosumab can reverse UVB-induced immunosuppression, the subjects will have previously been randomized to receive a single 1mL injection of either 60 mg denosumab (group A; 10 subjects) or 1 mL saline (group B; 10 subjects) two weeks before UVB exposure. CHS reactions elicited by DPCP rechallenge will be compared between the denosumab and saline groups.
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Change in dermal thickness: denosumab group vs placebo group of Cohort 2
Timeframe: Three weeks after sensitization to DPCP.