In vivo imaging of cytotoxic T cell infiltration and elimination of a solid tumor

Although the immune system evolved to fight infections, it may also attack and destroy solid tumors. In most cases, tumor rejection is initiated by CD8+ cytotoxic T lymphocytes (CTLs), which infiltrate solid tumors, recognize tumor antigens, and kill tumor cells. We use a combination of two-photon intravital microscopy and immunofluorescence on ordered sequential sections to analyze the infiltration and destruction of solid tumors by CTLs. We show that in the periphery of a thymoma growing subcutaneously, activated CTLs migrate with high instantaneous velocities. The CTLs arrest in close contact to tumor cells expressing their cognate antigen. In regions where most tumor cells are dead, CTLs resume migration, sometimes following collagen fibers or blood vessels. CTLs migrating along blood vessels preferentially adopt an elongated morphology. CTLs also infiltrate tumors in depth, but only when the tumor cells express the cognate CTL antigen. In tumors that do not express the cognate antigen, CTL infiltration is restricted to peripheral regions, and lymphocytes neither stop moving nor kill tumor cells. Antigen expression by tumor cells therefore determines both CTL motility within the tumor and profound tumor infiltration

Small Molecule Enhancers of Endosome-to-Cytosol Import Augment Anti-tumor Immunity

Cross-presentation of antigens by dendritic cells (DCs) is critical for initiation of anti-tumor immune responses. Yet, key steps involved in trafficking of antigens taken up by DCs remain incompletely understood. Here, we screen 700 US Food and Drug Administration (FDA)-approved drugs and identify 37 enhancers of antigen import from endolysosomes into the cytosol. To reveal their mechanism of action, we generate proteomic organellar maps of control and drug-treated DCs (focusing on two compounds, prazosin and tamoxifen). By combining organellar mapping, quantitative proteomics, and microscopy, we conclude that import enhancers undergo lysosomal trapping leading to membrane permeation and antigen release. Enhancing antigen import facilitates cross-presentation of soluble and cell-associated antigens. Systemic administration of prazosin leads to reduced growth of MC38 tumors and to a synergistic effect with checkpoint immunotherapy in a melanoma model. Thus, inefficient antigen import into the cytosol limits antigen cross-presentation, restraining the potency of anti-tumor immune responses and efficacy of checkpoint blockers

OA011-03. Clusterin, a natural ligand of DC-SIGN present in human semen inhibits HIV capture and transmission by dendritic cells

International audiencen.

IRX-2, a Novel Immunotherapeutic, Enhances Functions of Human Dendritic Cells

Background: In a recent phase II clinical trial for HNSCC patients, IRX-2, a cell-derived biologic, promoted T-cell infiltration into the tumor and prolonged overall survival. Mechanisms responsible for these IRX-2-mediated effects are unknown. We hypothesized that IRX-2 enhanced tumor antigen-(TA)-specific immunity by up-regulating functions of dendritic cells (DC). Methodology/Principal Findings: Monocyte-derived DC obtained from 18 HNSCC patients and 12 healthy donors were matured using IRX-2 or a mix of TNF-α, IL-1β and IL-6 ("conv. mix"). Multicolor flow cytometry was used to study the DC phenotype and antigen processing machinery (APM) component expression. ELISPOT and cytotoxicity assays were used to evaluate tumor-reactive cytotoxic T lymphocytes (CTL). IL-12p70 and IL-10 production by DC was measured by Luminex® and DC migration toward CCL21 was tested in transwell migration assays. IRX-2-matured DC functions were compared with those of conv. mix-matured DC. IRX-2-matured DC expressed higher levels (p<0.05) of CD11c, CD40, CCR7 as well as LMP2, TAP1, TAP2 and tapasin than conv. mix-matured DC. IRX-2-matured DC migrated significantly better towards CCL21, produced more IL-12p70 and had a higher IL12p70/IL-10 ratio than conv. mix-matured DC (p<0.05 for all). IRX-2-matured DC carried a higher density of tumor antigen-derived peptides, and CTL primed with these DC mediated higher cytotoxicity against tumor targets (p<0.05) compared to the conv. mix-matured DC. Conclusion: Excellent ability of IRX-2 to induce ex vivo DC maturation in HNSCC patients explains, in part, its clinical benefits and emphasizes its utility in ex vivo maturation of DC generated for therapy. © 2013 Schilling et al

Rab27a controls HIV-1 assembly by regulating plasma membrane levels of phosphatidylinositol 4,5-bisphosphate

During the late stages of the HIV-1 replication cycle, the viral polyprotein Pr55(Gag) is recruited to the plasma membrane (PM), where it binds phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and directs HIV-1 assembly. We show that Rab27a controls the trafficking of late endosomes carrying phosphatidylinositol 4-kinase type 2 α (PI4KIIα) toward the PM of CD4(+) T cells. Hence, Rab27a promotes high levels of PM phosphatidylinositol 4-phosphate and the localized production of PI(4,5)P2, therefore controlling Pr55(Gag) membrane association. Rab27a also controls PI(4,5)P2 levels at the virus-containing compartments of macrophages. By screening Rab27a effectors, we identified that Slp2a, Slp3, and Slac2b are required for the association of Pr55(Gag) with the PM and that Slp2a cooperates with Rab27a in the recruitment of PI4KIIα to the PM. We conclude that by directing the trafficking of PI4KIIα-positive endosomes toward the PM, Rab27a controls PI(4,5)P2 production and, consequently, HIV-1 replication.Universidad de Buenos Aires and CONICET doctoral fellowships, Agencia Nacional de Pro- moción Científica y Tecnológica (Argentina) grants: (2010-1681, 2012-00353), Creative and Novel Ideas in HIV Research Program, University of Alabama at Birmingham Center for AIDS Research funding grant P30 AI027767-24

Testing relationships: ethical arguments for screening with HbA1C

Since the 1990s, glycated haemoglobin (HbA1C) has been the gold standard for monitoring glycaemic control in people diagnosed as having either type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM). Discussions are underway about diagnosing diabetes mellitus on the basis of HbA1C titres and using HbA1C tests to screen for T2DM. These discussions have focused on the relative benefits for individual patients, with some attention directed towards reduced costs to healthcare systems and benefits to society. We argue that there are strong ethical reasons for adopting HbA1C-based diagnosis and T2DM screening that have not yet been articulated. The rationale includes the differential impact of HbA1C-based diabetic testing on disadvantaged groups, and what we are beginning to learn about HbA1C vis-à-vis population health. Although it is arguable that screening must primarily benefit the individual, using HbA1C to diagnose and screen for T2DM may promote a more just distribution of health resources and lead to advances in investigating, monitoring and tackling the social determinants of health

Exosomes Derived from M. Bovis BCG Infected Macrophages Activate Antigen-Specific CD4+ and CD8+ T Cells In Vitro and In Vivo

Activation of both CD4+ and CD8+ T cells is required for an effective immune response to an M. tuberculosis infection. However, infected macrophages are poor antigen presenting cells and may be spatially separated from recruited T cells, thus limiting antigen presentation within a granuloma. Our previous studies showed that infected macrophages release from cells small membrane-bound vesicles called exosomes which contain mycobacterial lipid components and showed that these exosomes could stimulate a pro-inflammatory response in naïve macrophages. In the present study we demonstrate that exosomes stimulate both CD4+ and CD8+ splenic T cells isolated from mycobacteria-sensitized mice. Although the exosomes contain MHC I and II as well as costimulatory molecules, maximum stimulation of T cells required prior incubation of exosomes with antigen presenting cells. Exosomes isolated from M. bovis and M. tuberculosis infected macrophages also stimulated activation and maturation of mouse bone marrow-derived dendritic cells. Interestingly, intranasal administration of mice with exosomes isolated from M. bovis BCG infected macrophages induce the generation of memory CD4+ and CD8+ T cells. The isolated T cells also produced IFN-γ upon restimulation with BCG antigens. The release of exosomes from infected macrophages may overcome some of the defects in antigen presentation associated with mycobacterial infections and we suggest that exosomes may be a promising M. tuberculosis vaccine candidate

Direct Presentation Is Sufficient for an Efficient Anti-Viral CD8+ T Cell Response

The extent to which direct- and cross-presentation (DP and CP) contribute to the priming of CD8+ T cell (TCD8+) responses to viruses is unclear mainly because of the difficulty in separating the two processes. Hence, while CP in the absence of DP has been clearly demonstrated, induction of an anti-viral TCD8+ response that excludes CP has never been purposely shown. Using vaccinia virus (VACV), which has been used as the vaccine to rid the world of smallpox and is proposed as a vector for many other vaccines, we show that DP is the main mechanism for the priming of an anti-viral TCD8+ response. These findings provide important insights to our understanding of how one of the most effective anti-viral vaccines induces immunity and should contribute to the development of novel vaccines