Antigen-Specific Transfer of Functional Programmed Death Ligand 1 from Human APCs onto CD8+ T Cells via Trogocytosis

Upon specific interaction with APCs, T cells capture membrane fragments and surface molecules in a process termed trogocytosis. In this study, we demonstrate that human Ag-specific CD8+ T cells acquire the coinhibitory molecule programmed death ligand 1 (PD-L1) from mature dendritic cells (mDC) and tumor cells in an Ag-specific manner. Immature dendritic cells were less effective in transferring surface molecules onto CD8+ T cells than mDCs. Interestingly, trogocytosis of PD-L1 requires cell–cell contact and cannot be induced by uptake of soluble proteins obtained from mDC lysates. The transfer process is impaired by inhibition of vacuolar ATPases in T cells as well as by fixation of dendritic cells. Of importance, CD8+ T cells that acquired PD-L1 complexes were able to induce apoptosis of neighboring programmed death 1–expressing CD8+ T cells. In summary, our data demonstrate that human CD8+ T cells take up functionally active PD-L1 from APCs in an Ag-specific fashion, leading to fratricide of programmed death 1–expressing, neighboring T cells. The transfer of functionally active coinhibitory molecules from APCs onto human CD8+ T cells could have a regulatory role in immune responses.