Impact of bacteria on the phenotype, functions, and therapeutic activities of invariant NKT cells in mice.

Invariant NKT (iNKT) cells are innate-like lymphocytes that recognize glycolipid antigens in the context of the MHC class I-like antigen-presenting molecule CD1d. In vivo activation of mouse iNKT cells with the glycolipid alpha-galactosylceramide (alpha-GalCer) results in the acquisition of a hyporesponsive (anergic) phenotype by these cells. Because iNKT cells can become activated in the context of infectious agents, here we evaluated whether iNKT cell activation by microorganisms can influence subsequent responses of these cells to glycolipid antigen stimulation. We found that mouse iNKT cells activated in vivo by multiple bacterial microorganisms, or by bacterial LPS or flagellin, became unresponsive to subsequent activation with alpha-GalCer. This hyporesponsive phenotype of iNKT cells required IL-12 expression and was associated with changes in the surface phenotype of these cells, reduced severity of concanavalin A-induced hepatitis, and alterations in the therapeutic activities of alpha-GalCer. These findings may have important implications for the development of iNKT cell-based therapies.

PD-1/PD-L blockade prevents anergy induction and enhances the anti-tumor activities of glycolipid-activated invariant NKT cells.

Invariant NKT (iNKT) cells recognize glycolipid Ags, such as the marine sponge-derived glycosphingolipid alpha-galactosylceramide (alphaGalCer) presented by the CD1d protein. In vivo activation of iNKT cells with alphaGalCer results in robust cytokine production, followed by the acquisition of an anergic phenotype. Here we have investigated mechanisms responsible for the establishment of alphaGalCer-induced iNKT cell anergy. We found that alphaGalCer-activated iNKT cells rapidly up-regulated expression of the inhibitory costimulatory receptor programmed death (PD)-1 at their cell surface, and this increased expression was retained for at least one month. Blockade of the interaction between PD-1 and its ligands, PD-L1 and PD-L2, at the time of alphaGalCer treatment prevented the induction iNKT cell anergy, but was unable to reverse established iNKT cell anergy. Consistently, injection of alphaGalCer into PD-1-deficient mice failed to induce iNKT cell anergy. However, blockade of the PD-1/PD-L pathway failed to prevent bacterial- or sulfatide-induced iNKT cell anergy, suggesting additional mechanisms of iNKT cell tolerance. Finally, we showed that blockade of PD-1/PD-L interactions enhanced the antimetastatic activities of alphaGalCer. Collectively, our findings reveal a critical role for the PD-1/PD-L costimulatory pathway in the alphaGalCer-mediated induction of iNKT cell anergy that can be targeted for the development of immunotherapies.

Thymus leukemia antigen controls intraepithelial lymphocyte function and inflammatory bowel disease.

Intestinal intraepithelial lymphocytes (IEL) bear a partially activated phenotype that permits them to rapidly respond to antigenic insults. However, this phenotype also implies that IEL must be highly controlled to prevent misdirected immune reactions. It has been suggested that IEL are regulated through the interaction of the CD8alpha alpha homodimer with the thymus leukemia (TL) antigen expressed by intestinal epithelial cells. We have generated and characterized mice genetically-deficient in TL expression. Our findings show that TL expression has a critical role in maintaining IEL effector functions. Also, TL deficiency accelerated colitis in a genetic model of inflammatory bowel disease. These findings reveal an important regulatory role of TL in controlling IEL function and intestinal inflammation.

The in vivo response of invariant natural killer T cells to glycolipid antigens.

Invariant natural killer T (iNKT) cells are a subset of T lymphocytes that recognizes glycolipid antigens presented by the major histocompatibility complex class I-related protein CD1d. Although iNKT cells have received a lot of attention as targets for the development of immunotherapies, few studies have investigated the in vivo response of iNKT cells to glycolipid antigen activation. Accumulating evidence indicates that iNKT cells generate a dynamic response to in vivo activation by glycolipid antigens that is characterized by surface receptor downmodulation, expansion, cytokine production, cross talk with other cells, homeostatic contraction, and acquisition of an anergic phenotype. These studies provide new insight into the biology of iNKT cells and have important implications for designing safe and effective iNKT cell-based vaccines and therapies.

Glycolipid ligands of invariant natural killer T cells as vaccine adjuvants.

Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that recognize glycolipid antigens in the context of the antigen-presenting molecule CD1d. Upon glycolipid antigen stimulation, iNKT cells rapidly produce copious amounts of immunomodulatory cytokines, leading to potent activation of a variety of innate and adaptive immune cells. These immune-potentiating properties of iNKT cells hold great promise for the development of vaccine adjuvants. This review aims to summarize the immunomodulatory activities of iNKT cell ligands and to discuss prospects for developing iNKT cell-based vaccine adjuvants.

c-Maf interacts with c-Myb to down-regulate Bcl-2 expression and increase apoptosis in peripheral CD4 cells.

The transcription factor c-Maf is critical for IL-4 production and the development of Th2 cells, which promote humoral immunity and protect against extracellular parasites. Yet, little else is known of c-Maf function in CD4 cells. Here, we identify a novel role for c-Maf in regulating susceptibility to apoptosis. Overexpression of c-Maf results in increased susceptibility of CD4 cells to apoptosis induced by multiple stimuli, including growth factor withdrawal, dexamethasone, irradiation, and TCR engagement. This effect is independent of Fas or p53; however, Bcl-2 expression is reduced in c-Maf Tg CD4 cells. Immunoprecipitation and Western blot analyses demonstrate that c-Maf-c-Myb complex formation is enhanced among T cells from c-Maf Tg mice compared to non-Tg littermates following TCR engagement. Unlike non-Tg T cells, c-Myb binding to the Bcl-2 promoter is not detectable in c-Maf Tg T cells by chromatin immunoprecipitation. In reporter assays, Bcl-2 promoter activity is reduced by c-Maf in a dose-dependent manner. Furthermore, transgene-mediated Bcl-2 expression corrects the apoptosis defect observed among c-Maf Tg CD4 cells. These data suggest that c-Maf can interact with c-Myb to reduce Bcl-2 expression, thereby limiting CD4 cell survival following TCR engagement.