Prolonged antigen survival and cytosolic export in cross-presenting human γδ T cells

Human blood V gamma 9V delta 2 T cells respond to signals from microbes and tumors and subsequently differentiate into professional antigen-presenting cells (gamma delta T-APCs) for induction of CD4(+) and CD8(+) T cell responses. gamma delta T-APCs readily take up and degrade exogenous soluble protein for peptide loading on MHCI, in a process termed antigen cross-presentation. The mechanisms underlying antigen cross-presentation are ill-defined, most notably in human dendritic cells (DCs), and no study has addressed this process in gamma delta T-APCs. Here we show that intracellular protein degradation and endosomal acidification were significantly delayed in gamma delta T-APCs compared with human monocyte-derived DCs (moDCs). Such conditions are known to favor antigen cross-presentation. In both gamma delta T-APCs and moDCs, internalized antigen was transported across insulin-regulated aminopeptidase (IRAP)-positive early and late endosomes; however, and in contrast to various human DC subsets, gamma delta T-APCs efficiently translocated soluble antigen into the cytosol for processing via the cytosolic proteasome-dependent cross-presentation pathway. Of note, gamma delta T-APCs cross-presented influenza antigen derived from virus-infected cells and from free virus particles. The robust cross-presentation capability appears to be a hallmark of gamma delta T-APCs and underscores their potential application in cellular immunotherapy.