To describe the clinical and histologic manifestations of skin reactions incidentally noted in patients with stage IV melanoma who were treated with up to 9 mg/kg of a humanized monoclonal antibody reactive against human cytotoxic T-lymphocyte antigen 4 (anti-CTLA-4) as a single agent every 3 weeks. Setting: Single-institution prospective study. Design: Patients treated with anti-CTLA-4 as a sole agent were prospectively referred for clinicopathologic characterization of skin reactions occurring during treatment. Main Outcome Measures: Specific clinicopathologic features were determined by means of a detailed history, a physical examination, conventional histologic analysis, antibody staining, and complete blood cell counts. Results: Nine (14%) of 63 consecutive patients treated with anti-CTLA-4 as a sole agent developed skin erup-See also page 175

CCL21, a lymphatic endothelial cell (LEC)-derived chemokine, and its receptor CCR7 regulate dendritic cell (DC) trafficking to lymph nodes (LN), but it is unclear how CCL21 expression is regulated. Oncostatin M (OSM) is an IL-6-like cytokine synthesized by activated DC and other leukocytes. In vitro, OSM (but not TNF-α) stimulated CCL21 mRNA and protein expression by human dermal microvascular EC (DMEC) in an ERK1/2-dependent fashion. Conditioned medium from OSM-treated DMEC stimulated CCL21-dependent chemotaxis of mouse bone marrow-derived DC (BMDC). Cultured BMDC expressed OSM, which was increased with the addition of LPS. Topical application of the contact-sensitizing hapten, trinitrochlorobenzene, resulted in enhanced OSM expression in the skin, whereas cutaneous injection of TNF-α did not. Injection of OSM into the footpad increased CCL21 mRNA expression in the draining LN by ∼10-fold and in mouse skin by ∼4-fold without increasing CCR7 mRNA. In vitro, OSM increased the permeability of DMEC and lung microvascular EC monolayers to FITC-dextran beads, and, in vivo, it enhanced accumulation of Evans blue dye in draining LN by ∼3-fold (p = 0.0291). Of note, OSM increased trafficking of BMDC injected in footpads to draining LN by 2-fold (p = 0.016). In summary, OSM up-regulates CCL21 expression in skin and draining regional LN. We propose that OSM is a regulator of CCL21 expression and endothelial permeability in skin, contributing to efficient migration of DC to regional LN.