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.