Suppression of dendritic cell function in cancer patients is thought to contribute to the inhibition of immune responses and disease progression. Molecular mechanisms of this suppression remain elusive, however. Here, we show that a fraction of blood monocyte-derived myeloid dendritic cells (MDCs) express B7-H1, a member of the B7 family, on the cell surface. B7-H1 could be further upregulated by tumor environmental factors. Consistent with this finding, virtually all MDCs isolated from the tissues or draining lymph nodes of ovarian carcinomas express B7-H1. Blockade of B7-H1 enhanced MDC-mediated T-cell activation and was accompanied by downregulation of T-cell interleukin (IL)-10 and upregulation of IL-2 and interferon (IFN)-gamma. T cells conditioned with the B7-H1-blocked MDCs had a more potent ability to inhibit autologous human ovarian carcinoma growth in non-obese diabetic-severe combined immunodeficient (NOD-SCID) mice. Therefore, upregulation of B7-H1 on MDCs in the tumor microenvironment downregulates T-cell immunity. Blockade of B7-H1 represents one approach for cancer immunotherapy.

Dendritic-cell (DC) trafficking and function in tumors is poorly characterized, with studies confined to myeloid DCs (DC1s). Tumors inhibit DC1 migration and function, likely hindering specific immunity. The role of plasmacytoid DCs (DC2s) in tumor immunity is unknown. We show here that malignant human ovarian epithelial tumor cells express very high levels of stromal-derived factor-1, which induces DC2 precursor (preDC2) chemotaxis and adhesion/transmigration, upregulates preDC2 very late antigen (VLA)-5, and protects preDC2s from tumor macrophage interleukin-10-induced apoptosis, all through CXC chemokine receptor-4. The VLA-5 ligand vascular-cell adhesion molecule-1 mediated preDC2 adhesion/transmigration. Tumor preDC2s induced significant T-cell interleukin-10 unrelated to preDC2 differentiation or activation state, and this contributed to poor T-cell activation. Myeloid precursor DCs (preDC1s) were not detected. Tumors may weaken immunity by attracting preDC2s and protecting them from the harsh microenvironment, and by altering preDC1 distribution.

The therapeutic efficacy of anthracyclines relies on antitumor immune responses elicited by dying cancer cells. How chemotherapy-induced cell death leads to efficient antigen presentation to T cells, however, remains a conundrum. We found that intratumoral CD11c(+)CD11b(+)Ly6C(hi) cells, which displayed some characteristics of inflammatory dendritic cells and included granulomonocytic precursors, were crucial for anthracycline-induced anticancer immune responses. ATP released by dying cancer cells recruited myeloid cells into tumors and stimulated the local differentiation of CD11c(+)CD11b(+)Ly6C(hi) cells. Such cells efficiently engulfed tumor antigens in situ and presented them to T lymphocytes, thus vaccinating mice, upon adoptive transfer, against a challenge with cancer cells. Manipulations preventing tumor infiltration by CD11c(+)CD11b(+)Ly6C(hi) cells, such as the local overexpression of ectonucleotidases, the blockade of purinergic receptors, or the neutralization of CD11b, abolished the immune system-dependent antitumor activity of anthracyclines. Our results identify a subset of tumor-infiltrating leukocytes as therapy-relevant antigen-presenting cells.

Long-lasting expansion of Vδ2neg γδ T cells is a hallmark of cytomegalovirus (CMV) infection in kidney transplant recipients. The ligands of these cells and their role remain elusive. To better understand their immune function, we generated γδ T cell clones from several transplanted patients. Numerous patient Vδ1+, Vδ3+, and Vδ5+ γδ T cell clones expressing diverse Vγ chains, but not control Vγ9Vδ2+ T clones, displayed strong reactivity against CMV-infected cells, as shown by their production of tumor necrosis factor-α. Vδ2neg γδ T lymphocytes could also kill CMV-infected targets and limit CMV propagation in vitro. Their anti-CMV reactivity was specific for this virus among herpesviridae and required T cell receptor engagement, but did not involve major histocompatibility complex class I molecules or NKG2D. Vδ2neg γδ T lymphocytes expressed receptors essential for intestinal homing and were strongly activated by intestinal tumor, but not normal, epithelial cell lines. High frequencies of CMV- and tumor-specific Vδ2neg γδ T lymphocytes were found among patients' γδ T cells. In conclusion, Vδ2neg γδ T cells may play a role in protecting against CMV and tumors, probably through mucosal surveillance of cellular stress, and represent a population that is largely functionally distinct from Vγ9Vδ2+ T cells.

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Perivascular infiltrates composed of macrophages and lymphocytes have been described in lung biopsies of patients displaying pulmonary arterial hypertension (PAH), suggesting that circulating inflammatory cells can be recruited in affected vessels. CX(3)C chemokine fractalkine is produced by endothelial cells and promotes leukocyte recruitment, but unlike other chemokines, it can capture leukocytes rapidly and firmly in an integrin-independent manner under high blood flow. We therefore hypothesized that fractalkine may contribute to pulmonary inflammatory cell recruitment in PAH. Expression and function of the fractalkine receptor (CX(3)CR1) were studied by use of triple-color flow cytometry on circulating T-lymphocyte subpopulations in freshly isolated peripheral blood mononuclear cells from control subjects and patients with PAH. Plasma-soluble fractalkine concentrations were measured by enzyme-linked immunosorbent assay. Finally, fractalkine mRNA and protein expression were analyzed in lung samples by reverse transcriptase-polymerase chain reaction or in situ hybridization and immunohistochemistry, respectively. In patients with PAH, CX(3)CR1 expression and function are upregulated in circulating T-lymphocytes, mostly of the CD4+ subset, and plasma soluble fractalkine concentrations are elevated, as compared with control subjects. Fractalkine mRNA and protein product are expressed in pulmonary artery endothelial cells. We conclude that inflammatory mechanisms involving chemokine fractalkine and its receptor CX(3)CR1 may have a role in the natural history of PAH.

In patients who are receiving prolonged antiretroviral treatment (ART), HIV can persist within a small pool of long-lived resting memory CD4+ T cells infected with integrated latent virus. This latent reservoir involves distinct memory subsets. Here we provide results that suggest a progressive reduction of the size of the blood latent reservoir around a core of less-differentiated memory subsets (central memory and stem cell-like memory (TSCM) CD4+ T cells). This process appears to be driven by the differences in initial sizes and decay rates between latently infected memory subsets. Our results also suggest an extreme stability of the TSCM sub-reservoir, the size of which is directly related to cumulative plasma virus exposure before the onset of ART, stressing the importance of early initiation of effective ART. The presence of these intrinsic dynamics within the latent reservoir may have implications for the design of optimal HIV therapeutic purging strategies.

IntroductionRegulatory T lymphocytes (Tregs) play a key role in controlling immune responses. Initially, 2 types of Tregs were identified. Natural (or constitutive) Tregs are generated in the thymus and they spontaneously express the transcription factor FOXP3 and high levels of CD25. Inducible (or adaptive) Tregs are generated by peripheral activation, particularly in the presence of IL-10 or TGF␤. However, the relationship between these 2 subpopulations has not been completely elucidated. Tregs inhibit immune responses by a combination of effects requiring direct contact with their targets and the production of inhibitory cytokines, including IL-10 and TGF␤. In addition to the coexpression of CD25 hi and FOXP3 and the production of IL-10 and TGF␤, several markers potentially characteristic of Tregs have been identified, but none of them has been unequivocally associated with the suppressive function of Tregs or with their classification into natural or inducible Tregs. [1][2][3][4] Antigen presentation by dendritic cells (DCs) leads to either immune stimulation or tolerance. The mechanisms underlying the decision of DCs to orientate the immune response toward one of these 2 opposite outcomes are not fully understood. Toleranceinducing DCs are also called regulatory DCs. One method used by regulatory DCs to prevent immune activation is to trigger T-lymphocyte anergy or apoptosis during antigen presentation. This involves production of the enzyme indoleamine 2,3-dioxygenase (IDO) and of nitric oxide by DCs. 5,6 The other method is to generate regulatory cells, including Tregs. Although IDO production by DCs may play a role in the induction of Tregs, 7 additional mechanisms are presumably involved. The state of maturation and activation of DCs is critical to Treg development: DCs activated and maturing in response to inflammatory stimuli trigger immune responses, but immature or "semimature" DCs, in contrast, induce tolerance, [8][9][10][11] and this is in part mediated by the generation of Tregs. [12][13][14][15] Phenotypically mature DCs can also be tolerogenic, and certain environmental signals can induce maturation of DCs in a tolerogenic mode. 10 IL-10, TGF␤, glucocorticoids (GCs), vasoactive intestinal peptide, vitamin D3, and antioxidative vitamins, used alone or in combination, orientate DC maturation to induce tolerance, [16][17][18][19][20][21][22][23][24] and Treg development has been demonstrated for several of these agents. 18,19,22,24 The molecular mechanisms involved in this switch of DC maturation toward regulatory DCs are largely unknown. Several tolerogenic agents down-regulate the NF-kB and p38 MAPK transduction pathways in DCs, which contrasts with the potency of inflammatory agents to activate them. 24,25 In addition, DCs from RelB-deficient mice induce immune tolerance and antigen-specific Tregs. 26 This suggests that modulation of NF-kB and p38 MAPK function contributes to the decision of DCs to differentiate into regulatory DCs.An intracellular factor called glucocorticoid-induced leucine ...