Danyvid Olivares-Villagómez

Glycolipid antigen induces long-term natural killer T cell anergy in mice

Natural killer T (NKT) cells recognize glycolipid antigens presented by the MHC class I-related glycoprotein CD1d. The in vivo dynamics of the NKT cell population in response to glycolipid activation remain poorly understood. Here, we show that a single administration of the synthetic glycolipid alpha-galactosylceramide (alpha-GalCer) induces long-term NKT cell unresponsiveness in mice. NKT cells failed to proliferate and produce IFN-gamma upon alpha-GalCer restimulation but retained the capacity to produce IL-4. Consequently, we found that activation of anergic NKT cells with alpha-GalCer exacerbated, rather than prevented, B16 metastasis formation, but that these cells retained their capacity to protect mice against experimental autoimmune encephalomyelitis. NKT cell anergy was induced in a thymus-independent manner and maintained in an NKT cell-autonomous manner. The anergic state could be broken by IL-2 and by stimuli that bypass proximal TCR signaling events. Collectively, the kinetics of initial NKT cell activation, expansion, and induction of anergy in response to alpha-GalCer administration resemble the responses of conventional T cells to strong stimuli such as superantigens. Our findings have important implications for the development of NKT cell-based vaccines and immunotherapies.

The response of natural killer T cells to glycolipid antigens is characterized by surface receptor down-modulation and expansion

CD1d-restricted natural killer T (NKT) cells are a subset of regulatory T cells that react with glycolipid antigens. Although preclinical studies have effectively targeted NKT cells for immunotherapy, little is known regarding the early in vivo response of these cells to antigenic stimulation. We have analyzed the early response of NKT cells to glycolipid antigens and bacterial infection by using specific reagents for tracking these cells. Our results demonstrate dramatic in vivo expansion and surface phenotype alterations after NKT cell activation with α-galactosylceramide. In addition, we show significant NK1.1 down-modulation on NKT cells in the setting of oral Salmonella infection. Our results indicate that in vivo activation of NKT cells leads to a dynamic response characterized by surface receptor down-modulation and expansion. These findings alter current understanding of NKT cell biology and should aid in the rational design of NKT cell-based immunotherapies.

Regulatory T cells in spontaneous autoimmune encephalomyelitis.

Summary: Spontaneous experimental autoimmune encephalomyelitis (EAE) develops in 100% of mice harboring a monoclonal myelin basic protein (MBP)‐specific CD4+αβ T‐cell repertoire. Monoclonality of the αβ T‐cell repertoire can be achieved by crossing MBP‐specific T‐cell receptor (TCR) transgenic mice with either RAG−/− mice or TCR α−/−/TCR β−/− double knockout mice. Spontaneous EAE can be prevented by a single administration of purified CD4+ splenocytes or thymocytes obtained from wild‐type syngeneic mice. The regulatory T cells (T‐reg) that protect from spontaneous EAE need not express the CD25 marker, as effective protection can be attained with populations depleted of CD25+ T cells. Although the specificity of the regulatory T cells is important for their generation or regulatory function, T cells that protect from spontaneous EAE can have a diverse TCR α and β chain composition. T‐reg cells expand poorly in vivo, and appear to be long lived. Finally, precursors for T‐reg are present in fetal liver as well as in the bone marrow of aging mice. We propose that protection of healthy individuals from autoimmune diseases involves several layers of regulation, which consist of CD4+CD25+ regulatory T cells, CD4+CD25− T‐reg cells, and anti‐TCR T cells, with each layer potentially operating at different stages of T‐helper cell‐mediated immune responses.

Quantitative and Qualitative Differences in the In Vivo Response of NKT Cells to Distinct α- and β-Anomeric Glycolipids

NKT cells represent a unique subset of immunoregulatory T cells that recognize glycolipid Ags presented by the MHC class I-like molecule CD1d. Because of their immunoregulatory properties, NKT cells are attractive targets for the development of immunotherapies. The prototypical NKT cell ligand α-galactosylceramide (α-GalCer), originally isolated from a marine sponge, has potent immunomodulatory activities in mice, demonstrating therapeutic efficacy against metastatic tumors, infections, and autoimmune diseases, but also has a number of adverse side effects. In vivo administration of α-GalCer to mice results in the rapid activation of NKT cells, which is characterized by cytokine secretion, surface receptor down-regulation, expansion, and secondary activation of a variety of innate and adaptive immune system cells. In this study, we have evaluated the in vivo immune response of mice to a set of structural analogues of α-GalCer. Our results show that, contrary to current thinking, β-anomeric GalCer can induce CD1d-dependent biological activities in mice, albeit at lower potency than α-anomeric GalCer. In addition, we show that the response of NKT cells to distinct GalCer differs not only quantitatively, but also qualitatively. These findings indicate that NKT cells can fine-tune their immune responses to distinct glycolipid Ags in vivo, a property that may be exploited for the development of effective and safe NKT cell-based immunotherapies.

Control of homeostatic proliferation by regulatory T cells

Homeostatic proliferation of T cells leads to the generation of effector/memory cells, which have the potential to cause harm to the host. The role of Tregs in the control of homeostatic proliferation is unclear. In this study we utilized mice that either harbor or lack Tregs as recipients of monoclonal or polyclonal T cells. We observed that while Tregs completely prevented cell division of T cells displaying low affinity for self ligands, they had a less marked, albeit significant, effect on cell cycle entry of T cells displaying higher affinity. The presence of Tregs resulted in a lower accumulation of T cells, enhanced apoptosis, and impaired differentiation to a cytokine-producing state. We conclude that Tregs play a major role in the control of homeostatic proliferation.

Repertoire Requirements of CD4+ T Cells That Prevent Spontaneous Autoimmune Encephalomyelitis

Spontaneous experimental autoimmune encephalomyelitis arises in 100% of mice exclusively harboring myelin basic protein-specific T cells, and can be prevented by a single injection of CD4+ T cells obtained from normal donors. Given the powerful regulatory effect of the transferred T cells, we further investigated their properties, and, in particular, their repertoire requirements. Transfer of monoclonal OVA-specific CD4+ T cells did not confer protection from disease even when present at very high proportions (about 80% of total lymphocytes). Lack of protection was also evident after immunization of these animals with OVA, indicating that not just any postthymic CD4+ T cells has the potential to become regulatory. However, protection was conferred by cells bearing limited TCR diversity, including cells expressing a single Vα4 TCR chain or cells lacking N nucleotides. We also investigated whether coexpression of the myelin basic protein-specific TCR with another TCR in a single cell would alter either pathogenesis or regulation. This was not the case, as myelin basic protein-specific/OVA-specific recombinase activating gene-1−/− double TCR transgenic mice still developed experimental autoimmune encephalomyelitis spontaneously even after immunization with OVA. Based on this evidence, we conclude that CD4+ T regulatory cells do not express canonical TCRs and that the altered signaling properties brought about by coexpression of two TCRs are not sufficient for the generation of regulatory T cells. Instead, our results indicate that regulatory T cells belong to a population displaying wide TCR diversity, but in which TCR specificity is central to their protective function.

Endonuclease G is required for early embryogenesis and normal apoptosis in mice

Endonuclease G (EndoG) is a nuclear-encoded mitochondrial protein reported to be important for both nuclear DNA fragmentation during apoptosis and mitochondrial DNA replication. To evaluate the in vivo function of EndoG, we have investigated the effects of EndoG deficiency in cells and mice. We found that EndoG homozygous mutant embryos die between embryonic days 2.5 and 3.5. Mitochondrial DNA copy numbers in ovulated oocytes from EndoG heterozygous mutant and wild-type mice are similar, suggesting that EndoG is involved in a cellular function unrelated to mitochondrial DNA replication. Interestingly, we found that cells from EndoG heterozygous mutant mice exhibit increased resistance to both tumor necrosis factor α- and staurosporine-induced cell death. Moreover, spontaneous cell death of spermatogonia in EndoG heterozygous mutant mice is significantly reduced compared with wild-type mice. DNA fragmentation is also reduced in EndoG+/- thymocytes and splenocytes compared with wild-type cells, as well as in EndoG+/- thymus in vivo compared with that of the wild-type mice, on activation of apoptosis. These findings indicate that EndoG is essential during early embryogenesis and plays a critical role in normal apoptosis and nuclear DNA fragmentation.

Impaired Autophagy, Defective T Cell Homeostasis, and a Wasting Syndrome in Mice with a T Cell–Specific Deletion of Vps34

Autophagy plays a critical role in multiple aspects of the immune system, including the development and function of T lymphocytes. In mammalian cells, the class III PI3K vacuolar protein sorting (Vps)34 is thought to play a critical role in autophagy. However, recent studies have cast doubt on the role of Vps34 in autophagy, at least in certain cell types. To study the effects of Vps34 on autophagy in T lymphocytes, we generated mice that selectively lack Vps34 in the T cell lineage. Vps34 ablation in T cells caused profound defects in autophagic flux, resulting in accumulation of cellular organelles and apoptosis. These animals exhibited normal intrathymic development of conventional T cells, but they were profoundly impaired in the intrathymic development of invariant NKT cells. In peripheral organs, T cell–specific ablation of Vps34 had a profound impact on T cell homeostasis and function. Furthermore, aged animals developed an inflammatory wasting syndrome characterized by weight loss, intestinal inflammation, and anemia. Consistent with this phenotype, Vps34 was required for the peripheral maintenance and function of CD4+Foxp3+ regulatory T cells. Collectively, our study reveals a critical role for Vps34 in autophagy and for the peripheral homeostasis and function of T lymphocytes.

Activated invariant NKT cells control central nervous system autoimmunity in a mechanism that involves myeloid-derived suppressor cells.

Invariant NKT (iNKT) cells are a subset of T lymphocytes that recognize glycolipid Ags presented by the MHC class I–related protein CD1d. Activation of iNKT cells with glycolipid Ags, such as the marine sponge–derived reagent α-galactosylceramide (α-GalCer), results in the rapid production of a variety of cytokines and activation of many other immune cell types. These immunomodulatory properties of iNKT cells have been exploited for the development of immunotherapies against a variety of autoimmune and inflammatory diseases, but mechanisms by which activated iNKT cells confer disease protection have remained incompletely understood. In this study, we demonstrate that glycolipid-activated iNKT cells cooperate with myeloid-derived suppressor cells (MDSCs) in protecting mice against the development of experimental autoimmune encephalomyelitis (EAE) in mice, an animal model for multiple sclerosis. We show that α-GalCer induced the expansion and immunosuppressive activities of MDSCs in the spleen of mice induced for development of EAE. Disease protection in these animals also correlated with recruitment of MDSCs to the CNS. Depletion of MDSCs abrogated the protective effects of α-GalCer against EAE and, conversely, adoptive transfer of MDSCs from α-GalCer-treated mice ameliorated passive EAE induced in recipient animals. The cytokines GM-CSF, IL-4, and IFN-γ, produced by activated iNKT cells, and inducible NO synthase, arginase-1, and IL-10 produced by MDSCs, contributed to these effects. Our findings have revealed cooperative immunosuppressive interactions between iNKT cells and MDSCs that might be exploited for the development of improved immunotherapies for multiple sclerosis and other autoimmune and inflammatory diseases.

Mucosal memory CD8 + T cells are selected in the periphery by an MHC class I molecule

The presence of immune memory at pathogen-entry sites is a prerequisite for protection. Nevertheless, the mechanisms that warrant immunity at peripheral interfaces are not understood. Here we show that the nonclassical major histocompatibility complex (MHC) class I molecule thymus leukemia antigen (TL), induced on dendritic cells interacting with CD8αα on activated CD8αβ+ T cells, mediated affinity-based selection of memory precursor cells. Furthermore, constitutive expression of TL on epithelial cells led to continued selection of mature CD8αβ+ memory T cells. The memory process driven by TL and CD8αα was essential for the generation of CD8αβ+ memory T cells in the intestine and the accumulation of highly antigen-sensitive CD8αβ+ memory T cells that form the first line of defense at the largest entry port for pathogens.