Marginating dendritic cells of the tumor microenvironment cross-present tumor antigens and stably engage tumor-specific T cells.

The nature and site of tumor-antigen presentation to immune T cells by bone-marrow-derived cells within the tumor microenvironment remains unresolved. We generated a fluorescent mouse model of spontaneous immunoevasive breast cancer and identified a subset of myeloid cells with significant similarity to dendritic cells and macrophages that constitutively ingest tumor-derived proteins and present processed tumor antigens to reactive T cells. Using intravital live imaging, we determined that infiltrating tumor-specific T cells engage in long-lived interactions with these cells, proximal to the tumor. In vitro, these cells capture cytotoxic T cells in signaling-competent conjugates but do not support full activation or sustain cytolysis. The spatiotemporal dynamics revealed here implicate nonproductive interactions between T cells and antigen-presenting cells on the tumor margin.

Myosin-IIA and ICAM-1 regulate the interchange between two distinct modes of T cell migration.

How T cells achieve rapid chemotactic motility under certain circumstances and efficient cell surface surveillance in others is not fully understood. We show that T lymphocytes are motile in two distinct modes: a fast "amoeboid-like" mode, which uses sequential discontinuous contacts to the substrate; and a slower mode using a single continuously translating adhesion, similar to mesenchymal motility. Myosin-IIA is necessary for fast amoeboid motility, and our data suggests that this occurs via cyclical rear-mediated compressions that eliminate existing adhesions while licensing subsequent ones at the front of the cell. Regulation of Myosin-IIA function in T cells is thus a key mechanism to regulate surface contact area and crawling velocity within different environments. This can provide T lymphocytes with motile and adhesive properties that are uniquely suited toward alternative requirements for immune surveillance and response.

A synaptic basis for paracrine interleukin-2 signaling during homotypic T cell interaction.

T cells slow their motility, increase adherence, and arrest after encounters with antigen-presenting cells (APCs) bearing peptide-MHC complexes. Here, we analyzed the cell-cell communication among activating T cells. In vivo and in vitro, activating T cells associated in large clusters that collectively persisted for >30 min, but they also engaged in more transient interactions, apparently distal to APCs. Homotypic aggregation was driven by LFA-1 integrin interactions. Ultrastructural analysis revealed that cell-cell contacts between activating T cells were organized as multifocal synapses, and T cells oriented both the microtubule-organizing complex and interleukin-2 (IL-2) secretion toward this synapse. T cells engaged in homotypic interactions more effectively captured IL-2 relative to free cells. T cells receiving paracrine synaptic IL-2 polarized their IL-2 signaling subunits into the synaptic region and more efficiently phosphorylated the transcription factor STAT5, likely through a synapse-associated signaling complex. Thus, synapse-mediated cytokine delivery accelerates responses in activating T cells.