Extended presentation of specific MHC-peptide complexes by mature dendritic cells compared to other types of antigen-presenting cells

Dendritic cells are known as the most potent antigen-presenting cells for the induction of T cell-mediated immune responses. To discriminate between the presentation of antigens and the co-stimulatory aspects of this high immunostimulatory capacity, we used recombinant antibodies with T cell receptor-like specificity to detect defined MHC-peptide complexes on living cells. Mature human dendritic cells (mDC) were compared with immature DC (iDC), monocytes, CD4⁺ T lymphocytes, melanoma cells, T2 cells and B lymphoblastoid cells for their capacity to present MHC class I-restricted tumor-associated T cell epitopes and were found to display the specific peptides two to six times longer than other cells. The most short-lived peptide had an average half-life of 8.7 h on mDC vs. 3.5 h on B lymphoblastoid cells, while the most long-lived peptide had a half-life of 118.5 h vs. 20.7 h on these two cell types. The decay kinetics of specific MHC-peptide complexes on OC were among the fastest observed. The high potency of dendritic cells to induce specific T cell responses is thus based, in addition to the expression of co-stimulatory molecules, on an extended antigenic memory, which increases the likelihood and the extent of contacts between dendritic cells and antigen-specific T cells.