CD40-ligated dendritic cells effectively expand melanoma-specific CD8(+) CTLs and CD4(+) IFN-gamma-producing T cells from tumor-infiltrating lymphocytes

Professional APC, notably dendritic cells (DC), are necessary for stimulati on and expansion of naive T cells. By means of murine models, the interacti on between CD40 on DC and its ligand CD154 has been recognized as an import ant element for conditioning of DC to prime and expand CTL, We translated t hese findings into the human system, scrutinizing the ability of DC to init iate clonal expansion of single T cells. DC generated under completely auto logous conditions from peripheral blood monocytes were cocultured at a rate of 0.3 cell/well with melanoma-infiltrating T cells; this procedure guaran teed that either a CD4(+) or a CD8(+) cell interacted with the DC, thus avo iding the contact of more than one T cell to the DC. In the absence of furt her stimulation, this cloning protocol yielded almost exclusively CD4(+) T cell clones that predominantly exhibited a Th2 phenotype, However, cross-li nking of CD40 on DC resulted in the induction of IFN-gamma-producing Th1 CD 4(+) T cell clones, In addition, CD40-activated DC were capable of expandin g CD8(+) CTL clones. The ratio of CD4 to CD8 T cell clones corresponded to the ratio present in the initial tumor-infiltrating lymphocyte preparation. The CTL clones efficiently lysed autologous tumor cells whereas autologous fibroblasts or MHC-mismatched melanoma cells were not killed. Our findings support the critical role of CD40/CD154 interactions for the induction of cellular immune responses.