Programmed cell death-1 (PD-1) is an inhibitory coreceptor for T lymphocytes that provides feedback inhibition of T cell activation. Although PD-1’s expression on T cells is known to be activation dependent, the factors that determine the timing, intensity, and duration of PD-1 expression in immune reactions are not fully understood. To address this question, we performed a fine mapping analysis of a conserved 5′-flanking region of the PD-1 gene and identified a putative IFN stimulation response element, which was responsible for PD-1 transcription in the 2B4.11 T cell line. Consistent with this finding, activation by IFN-α enhanced both the induction and maintenance of PD-1 expression on TCR-engaged primary mouse T cells through an association IFN-responsive factor 9 (IRF9) to the IFN stimulation response element. Furthermore, PD-1 expression on Ag-specific CD8+ T cells was augmented by IFN-α in vivo. We propose that strong innate inflammatory responses promote primary T cell activation and their differentiation into effector cells, but also cause an attenuated T cell response in sustained immune reactions, at least partially through type I IFN-mediated PD-1 transcription. Based on this idea, we demonstrate that IFN-α administration in combination with PD-1 blockade in tumor-bearing mice effectively augments the antitumor immunity, and we propose this as a novel and rational approach for cancer immunotherapy.

Although dense animal communities at hydrothermal vents and cold seeps rely on symbioses with chemoautotrophic bacteria [1, 2], knowledge of the mechanisms underlying these chemosynthetic symbioses is still fragmentary because of the difficulty in culturing the symbionts and the hosts in the laboratory. Deep-sea Calyptogena clams harbor thioautotrophic bacterial symbionts in their gill epithelial cells [1, 2]. They have vestigial digestive tracts and nutritionally depend on their symbionts [3], which are vertically transmitted via eggs [4]. To clarify the symbionts' metabolic roles in the symbiosis and adaptations to intracellular conditions, we present the complete genome sequence of the symbiont of Calyptogena okutanii. The genome is a circular chromosome of 1,022,154 bp with 31.6% guanine + cytosine (G + C) content, and is the smallest reported genome in autotrophic bacteria. It encodes 939 protein-coding genes, including those for thioautotrophy and for the syntheses of almost all amino acids and various cofactors. However, transporters for these substances to the host cell are apparently absent. Genes that are unnecessary for an intracellular lifestyle, as well as some essential genes (e.g., ftsZ for cytokinesis), appear to have been lost from the symbiont genome. Reductive evolution of the genome might be ongoing in the vertically transmitted Calyptogena symbionts.

Accumulating evidence suggests that PD-1, an immuno-inhibitory receptor expressed on activated T cells, regulates peripheral T cell tolerance. In particular, PD-1 is involved in the induction and/or maintenance of T cells’ intrinsic unresponsiveness to previously encountered Ags, although the mechanism is yet to be determined. We used a simple experimental model to dissect the mechanism for anergy establishment, in which 2C TCR transgenic rag2−/− PD-1+/+ mice were anergized by a single injection of a cognate peptide. Interestingly, 2C rag2−/− PD-1−/− mice were totally resistant to anergy induction by the same treatment; thus, PD-1 was responsible for anergy induction. Furthermore, PD-1 expression was induced within 24 h of the initial Ag exposure. The establishment of anergy was associated with a marked down-regulation of IL-2 from the CD8+ T cells. In fact, IL-2 blockade resulted in anergy even in 2C rag2−/−PD-1−/− T cells. Furthermore, the complementation of the IL-2 signal in 2C rag2−/− PD-1+/+ mice reversed the anergy induction. We propose that CD8+ T cell anergy is induced by a reduction of cell-autonomous IL-2 synthesis, which is caused by the quick expression of PD-1 in response to Ag stimulation and the subsequent stimulation of this receptor by its ligands on surrounding cells.

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The nitrile hydratase (NHase) from Rhodococcus sp. N-771 is a photoreactive enzyme that is inactivated on nitrosylation of the non-heme iron center and activated on photo-dissociation of nitric oxide (NO). The nitrile hydratase operon consists of six genes encoding NHase regulator 2, NHase regulator 1, amidase, NHase alpha subunit, NHase beta subunit and NHase activator. We overproduced the NHase in Escherichia coli using a T7 expression system. The NHase was functionally expressed in E. coli only when the NHase activator encoded downstream of the beta subunit gene was co-expressed and the transformant was grown at 30 degrees C or less. A ligand cysteine, alphaCys112, of the recombinant NHase was also post-translationally modified to a cysteine-sulfinic acid similar to for the native NHase. Although another modification of alphaCys114 could not be identified because of the instability under acidic conditions, the recombinant NHase could be reversibly inactivated by nitric oxide.