Introduction␥␦ T cells are key players in the immune surveillance of cellular distress, thanks to their ability to recognize conserved determinants up-regulated after inflammation, infection, or cell transformation. 1,2 Although ␥␦ T-cell receptors (TCRs) contribute to detection of danger-associated determinants, ligands for these receptors have been identified in a few cases only. 3 Thus, the antigenic specificity of ␥␦ T cells and their fine activation modalities in response to cell stress remain largely unknown.One of the best studied ␥␦ T-cell subsets in humans expresses V␥9V␦2 TCR and predominates in blood, composing several percent of the whole peripheral lymphoid pool in most adults. V␥9V␦2 T cells are activated by nonpeptidic phosphorylated isoprenoid pathway metabolites, 4-6 hereafter referred to as phosphoagonists (PAg). Natural V␥9V␦2-stimulating PAg include isopentenyl pyrophosphate (IPP), 7 a metabolite of the mevalonate pathway found in mammalian cells and the desoxyxylulose phosphate pathway shared by many microorganisms, and hydroxy-methyl-butyl-pyrophosphate, 8 an intermediate of the latter pathway. PAg detection by ␥␦ T cells underlies their broad reactivity toward infected and transformed cells. Indeed, tumor cell recognition by V␥9V␦2 T cells is linked to enhanced production of the weak agonist IPP, resulting from increased cell metabolism and cholesterol biosynthesis. Accordingly, pharmacologic inhibitors of the mevalonate pathway that up-regulate (eg, aminobisphosphonates, NBP) or down-regulate (eg, statins) IPP production, respectively, increase or decrease antitumor V␥9V␦2 T-cell responses. 9,10 Moreover, because of the high V␥9V␦2 T cell-stimulating activity of the microbial agonist hydroxy-methyl-butyl-pyrophosphate, V␥9V␦2 T-cell responses are elicited by infected cells producing even traces of this PAg. 8 Although PAg-induced activation is restricted to V␥9V␦2 T cells and can be conferred by V␥9V␦2 TCR gene transfer, 11,12 attempts to detect cognate interactions between PAg and V␥9V␦2 TCR have failed so far. 13 So how V␥9V␦2 T cells sense PAg remains an enigma. PAg rapidly induce Ca 2ϩ signaling and activation of V␥9V␦2 T-cell clones, but this requires cell-to-cell contact, suggesting the implication of additional target cell surface receptors in this phenomenon. 11,14 PAg elicit V␥9V␦2 T-cell responses against basically all human cells, irrespective of their tissue origin, but do not induce recognition of any murine target cells. Therefore, the putative target cell receptors involved in PAg-mediated T-cell activation are expected to be broadly expressed by human, but not murine, cells.Activation of antigen-stimulated T cells is tuned by interactions involving T cell-derived CD28-related receptors and target cellderived B7-related counter-receptors, 15 which family includes members, such as Skint and butyrophilin (BTN) receptors. The mandatory role played by Skint-1 in the intrathymic positive There is an Inside Blood commentary on this article in this issue.The online version of this...

NK cells are a major component of the antitumor immune response and are involved in controlling tumor progression and metastases in animal models. Here, we show that dysfunction of these cells accompanies human breast tumor progression. We characterized human peripheral blood NK (p-NK) cells and malignant mammary tumor-infiltrating NK (Ti-NK) cells from patients with noninvasive and invasive breast cancers. NK cells isolated from the peripheral blood of healthy donors and normal breast tissue were used as controls. With disease progression, we found that expression of activating NK cell receptors (such as NKp30, NKG2D, DNAM-1, and CD16) decreased while expression of inhibitory receptors (such as NKG2A) increased and that this correlated with decreased NK cell function, most notably cytotoxicity. Importantly, Ti-NK cells had more pronounced impairment of their cytotoxic potential than p-NK cells. We also identified several stroma-derived factors, including TGF-β1, involved in tumor-induced reduction of normal NK cell function. Our data therefore show that breast tumor progression involves NK cell dysfunction and that breast tumors model their environment to evade NK cell antitumor immunity. This highlights the importance of developing future therapies able to restore NK cell cytotoxicity to limit/prevent tumor escape from antitumor immunity. IntroductionBreast cancer (BC) is the primary cause of cancer deaths in women. The main cause of this mortality is the metastatic spread to other organs (1). Metastasis occurs when tumor cells acquire invasive features (2) and the ability to escape from antitumor immunity (3, 4). Defects in antitumor immunity may also facilitate BC occurrence. Indeed, mice deficient in IFN-γ production spontaneously develop mammary tumors (5). Breast tumor cells transplanted into NOD/SCID mice (which lack adaptive immunity) form noninvasive tumors, whereas the same cells transplanted into NOD/SCID/γ-c null mice (no adaptive immunity and no NK cells) form invasive tumors that metastasize rapidly (6). This effect is strictly dependent on NK cells (7). Similarly, in a highly metastatic model, BC metastasized to the lung only after elimination of NK cells by Tregs (8).Advanced BC patients show defects in antitumor immunity, such as alterations of DC maturation (9) and an increase in Treg infiltrates (10). Major impairment of peripheral blood NK cell maturation and cytotoxic functions has also been reported in metastatic BC (11). Several gene expression profiling studies have shown that a better outcome is associated with a strong cytotoxic infiltrate containing NK cells (12)(13)(14)(15). These data suggest that BC progression is linked to antitumor immunity efficiency and particularly to NK cells. However, the precise relationships between NK cells and BC progression in humans have not been studied so far.

Immunohistochemical analysis of FOXP3 in primary breast tumors showed that a high number of tumor-infiltrating regulatory T cells (Ti-Treg) within lymphoid infiltrates surrounding the tumor was predictive of relapse and death, in contrast to those present within the tumor bed. + , and CD8 + T cells was documented within lymphoid infiltrates. Altogether, these results show that Treg are selectively recruited within lymphoid infiltrates and activated by mature DC likely through TAA presentation, resulting in the prevention of effector T-cell activation, immune escape, and ultimately tumor progression. This study sheds new light on Treg physiology and validates CCR4/CCL22 and ICOS as therapeutic targets in breast tumors, which represent a major health problem.