Purification and characterization of multisquamase, the prothrombin activator present in Echis multisquamatus venom

Escape from immune surveillance is critical for tumor progression in metastatic melanoma. We assessed the function of melanoma-derived dendritic cells (DCs) in patients presenting simultaneously with responding (rM) or progressing (pM) melanoma metastases. These rare coincidences allowed us to compare syngeneically the function of tumor DCs. CD83+ DCs were purified freshly from large responding (rDCs) or progressing (pDCs) metastases following chemoimmunotherapy. rDCs were 5 times more potent inducers of allogeneic T-cell proliferation than the pDCs that were used as control. Phenotypic analysis showed a marked depression of CD86 expression on pDCs. Culture supernatants from pM showed production of Th2-type cytokines interleukin-10 (IL-10)], whereas a Th1 pattern IL-2, interferon-gamma (IFN-gamma), IL-12) predominated in rM. The IL-10 detected in progressing metastases was directly derived from melanoma cells. Culture supernatants from metastases applied to DC-supported allo-MLR assays suppressed T-cell responses by 50-75% in the case of pM, but not rM. Finally, in a co-stimulation-dependent anti-CD3 tolerance assay, pDCs (but not rDCs) induced anergy in syngeneic CD4+ T cells. Anergy could be overcome by addition of IL-12 or IL-2. Our results show that melanoma-derived factors convert DC-antigen presenting cell function to tolerance induction against tumor tissue, changing tumor DCs to "silencers" of anti-tumoral immune responses.