Dexamethasone turns tumor antigen-presenting cells into tolerogenic dendritic cells with T cell inhibitory functions.

BACKGROUND: Dendritic cells (DCs) are usually immunogenic, but they are also capable of inducing tolerance under anti-inflammatory conditions. Immunotherapy based on autologous DCs loaded with an allogeneic melanoma cell lysate (TRIMEL/DCs) induces immunological responses and increases melanoma patient survival. Glucocorticoids can suppress DC maturation and function, leading to a DC-mediated inhibition of T cell responses. METHODS: The effect of dexamethasone, a glucocorticoid extensively used in cancer therapies, on TRIMEL/DCs phenotype and immunogenicity was examined. RESULTS: Dexamethasone induced a semi-mature phenotype on TRIMEL/DC with low maturation surface marker expressions, decreased pro-inflammatory cytokine induction (IL-1ß and IL-12) and increased release of regulatory cytokines (IL-10 and TGF-ß). Dexamethasone-treated TRIMEL/DCs inhibited allogeneic CD4+ T cell proliferation and cytokine release (IFNγ, TNF-α and IL-17). Co-culturing melanoma-specific memory tumor-infiltrating lymphocytes with dexamethasone-treated TRIMEL/DC inhibited proliferation and effector T cell activities, including cytokine secretion and anti-melanoma cytotoxicity. CONCLUSIONS: These findings suggest that dexamethasone repressed melanoma cell lysate-mediated DC maturation, generating a potent tolerogenic-like DC phenotype that inhibited melanoma-specific effector T cell activities. These results suggest that dexamethasone-induced immunosuppression may interfere with the clinical efficacy of DC-based melanoma vaccines, and must be taken into account for optimal design of cellular therapy against cancer.

Heat-shock induction of tumor-derived danger signals mediates rapid monocyte differentiation into clinically effective dendritic cells.

PURPOSE: This study characterizes, biologically and clinically, a novel type of dendritic cells (DC) produced in the short term and called tumor antigen-presenting cells (TAPCells). In particular, we identified factors present in a lysate derived from heat-shocked allogeneic melanoma cells (TRIMEL) that are associated with TAPCells' enhanced capability to induce CD8(+) T-cell responses in vitro and in vaccinated melanoma patients. EXPERIMENTAL DESIGN: First, extensive phenotypic and functional characterization of TAPCells was performed, followed by vaccination of 45 melanoma patients with four doses of TAPCells over a period of 2 months. Specific delayed-type hypersensitivity (DTH) reaction was analyzed posttreatment and correlated with overall survival rates. Furthermore, heat-shock (HS)-induced factors present in TRIMEL and their effects on DC activation were identified and studied. RESULTS: TRIMEL induced a committed, mature, DC-like phenotype in TAPCells and effectively activated melanoma-specific CD4(+) and CD8(+) T cells. Clinically, 64% of vaccinated patients showed positive DTH reaction against TRIMEL, and this was associated with improved overall survival. HS treatment of tumor cells increased calreticulin (CRT) plasma membrane translocation and induced the release of high-mobility group box 1 proteins (HMGB1). Both CRT and HMGB1 mobilization were associated with enhanced TAPCells' maturation and antigen (Ag) cross-presentation, respectively. DTH infiltration analysis revealed the presence of CD8(+)/CD45RO(+) T cells, thus confirming TAPCells' ability to cross-present Ags in vivo. CONCLUSIONS: Our results indicate that lysates derived from heat-shocked tumor cells are an optimal source of tumor-associated Ags, which are crucial for the generation of DCs with improved Ag cross-presentation capacity and clinically effective immunogenicity.