There is consensus that an optimized cancer vaccine will have to induce not only CD8+ cytotoxic but also CD4+ T helper (Th) cells, particularly interferon (IFN)-γ–producing, type 1 Th cells. The induction of strong, ex vivo detectable type 1 Th cell responses has not been reported to date. We demonstrate now that the subcutaneous injection of cryopreserved, mature, antigen-loaded, monocyte-derived dendritic cells (DCs) rapidly induces unequivocal Th1 responses (ex vivo detectable IFN-γ–producing effectors as well as proliferating precursors) both to the control antigen KLH and to major histocompatibility complex (MHC) class II–restricted tumor peptides (melanoma-antigen [Mage]-3.DP4 and Mage-3.DR13) in the majority of 16 evaluable patients with metastatic melanoma. These Th1 cells recognized not only peptides, but also DCs loaded with Mage-3 protein, and in case of Mage-3DP4–specific Th1 cells IFN-γ was released even after direct recognition of viable, Mage-3–expressing HLA-DP4+ melanoma cells. The capacity of DCs to rapidly induce Th1 cells should be valuable to evaluate whether Th1 cells are instrumental in targeting human cancer and chronic infections.

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Skin mast cells are typically located in the perivascular or perineural connective tissue. We observed that HMC-1 mast cells growing in suspension adhered efficiently to (> 90% of cells) and spread on top of fibroblast monolayers and to a lesser degree on purified extracellular matrix proteins. Since adhesive interactions determine cell migration and tissue localization we studied the mechanism. It was found that HMC-1 cells attach to collagen I and fibronectin, laminin, collagen IV and vitronectin, but not to collagens III and VI or hyaluronic acid. Adhesion to fibronectin, collagen I and laminin was completely inhibited by mAbs blocking beta 1-integrins, whereas adhesion of HMC-1 cells to vitronectin was inhibited by anti-alpha v-chain mAbs. However, attachment of HMC-1 cells to fibroblasts was not influenced by mAbs blocking beta 1- or alpha v-chain function, by RGD peptides or by mAbs interfering with other receptors, most notably c-kit. Identical results were obtained with normal mast cells isolated from human foreskin. These results indicate that human mast cells attach to fibroblasts independently of beta 1- or alpha v-integrins as well as of c-kit receptor-mediated mechanisms. The functional characteristics observed (i.e. only partial sensitivity to trypsin and EDTA, no increase in trypsin sensitivity by pretreatment with EDTA) suggest that cadherin receptors were not involved, and it is likely that the adhesion process observed involved not-yet-defined heterotypic cell-cell adhesion receptors.