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The contribution of B cells to immunity against many infectious diseases is unquestionably important and well characterized. Here, we sought to determine the role of B cells in the induction of T helper 1 (TH1) CD4+ T cells upon vaccination with a tuberculosis (TB) antigen combined with a TLR4 agonist. We used B-cell deficient mice (μMT−/−), tetramer-positive CD4+ T cells, markers of memory ‘precursor’ effector cells (MPECs), and T-cell adoptive transfers and demonstrated that the early antigen-specific cytokine-producing TH1 responses are unaffected in the absence of B cells, however MPEC induction is strongly impaired resulting in a deficiency of the memory TH1 response in μMT−/- mice. We further show that antigen-presentation by B cells is necessary for their role in MPEC generation using B-cell adoptive transfers from wildtype or MHC class II knock-out mice into μMT−/− mice. Our study challenges the view that B-cell deficiency exclusively alters the TH1 response at memory time-points. Collectively, our results provide new insights on the multifaceted roles of B cells which will have a high impact on vaccine development against several pathogens including those requiring TH1 cell-mediated immunity. This article is protected by copyright. All rights reserved

Infection with Leishmania parasites results in a range of clinical manifestations and outcomes, the most severe of which is visceral leishmaniasis (VL). Vaccination will likely provide the most effective long-term control strategy, as the large number of vectors and potential infectious reservoirs renders sustained interruption of Leishmania parasite transmission extremely difficult. Selection of the best vaccine is complicated because, although several vaccine antigen candidates have been proposed, they have emerged following production in different platforms. To consolidate the information that has been generated into a single vaccine platform, we expressed seven candidates as recombinant proteins in E. coli. After verifying that each recombinant protein could be recognized by VL patients, we evaluated their protective efficacy against experimental L. donovani infection of mice. Administration in formulation with the Th1-potentiating adjuvant GLA-SE indicated that each antigen could elicit antigen-specific Th1 responses that were protective. Considering the ability to reduce parasite burden along with additional factors such as sequence identity across Leishmania species, we then generated a chimeric fusion protein comprising a combination of the 8E, p21 and SMT proteins. This E. coli –expressed fusion protein was also demonstrated to protect against L. donovani infection. These data indicate a novel recombinant vaccine antigen with the potential for use in VL control programs.

Cytotoxic CD8 T lymphocytes (CTLs) play a pivotal role in the control of infection. Activated CTLs, however, often lose effector function during chronic infection. PD-1 receptor and its ligand PD-L1 of the B7/CD28 family function as a T cell coinhibitory pathway and are emerging as major regulators converting effector CTLs into exhausted CTLs during chronic infection with human immunodeficiency virus, hepatitis B virus, hepatitis C virus, and other pathogens capable of establishing chronic infections. Importantly, blockade of the PD-1/PD-L1 pathway is able to restore functional capabilities to exhausted CTLs and early clinical trials have shown promise. Further research will reveal how chronic infection induces upregulation of PD-1 on CTLs and PD-L1 on antigen-presenting cells and other tissue cells and how the PD-1/PD-L1 interaction promotes CTLs exhaustion, which is crucial for developing effective prophylactic and therapeutic vaccination against chronic infections.

Summary We report that coactivator SAGA, containing the HAT Gcn5p, occupies the GAL1 and ARG1 coding sequences during transcriptional induction, dependent on PIC assembly and Ser5 phosphorylation of the Pol II CTD. Induction of GAL1 increases H3 acetylation per nucleosome in the ORF, dependent on SAGA integrity but not the alternative Gcn5p-HAT complex ADA. Unexpectedly, H3 acetylation in ARG1 coding sequences does not increase during induction due to the opposing activities of multiple HDAs associated with the ORF. Remarkably, inactivation of Gcn5p decreases nucleosome eviction from both GAL1 and a long (∼8 kb) ORF transcribed from the GAL1 promoter. This is associated with reduced Pol II occupancy at the 3′ end and decreased mRNA production, selectively, for the long ORF. Gcn5p also enhances H3-K4 trimethylation in the ARG1 ORF and bulk histones. Thus, Gcn5p, most likely in SAGA, stimulates modification and eviction of nucleosomes in transcribed coding sequences and promotes Pol II elongation.

B7x (B7-H4 or B7S1) is an inhibitory member of the B7 family of T cell costimulation. It is expressed in low levels in healthy peripheral tissues, such as the lung epithelium, but is overexpressed in a variety of human cancers with negative clinical associations, including metastasis. However, the function of B7x in the context of cancer, whether expressed on cancer cells or on surrounding “host” tissues, has not been elucidated in vivo. We used the 4T1 metastatic breast cancer model and B7x knockout (B7x −/−) mice to investigate the effect of host tissue–expressed B7x on cancer. We found that 4T1 cells were B7x negative in vitro and in vivo, and B7x−/− mice had significantly fewer lung 4T1 tumor nodules than did wild-type mice. Furthermore, B7x−/− mice showed significantly enhanced survival and a memory response to tumor rechallenge. Mechanistic studies revealed that the presence of B7x correlated with reduced general and tumor-specific T cell cytokine responses, as well as with an increased infiltration of immunosuppressive cells, including tumor-associated neutrophils, macrophages, and regulatory T cells, into tumor-bearing lungs. Importantly, tumor-associated neutrophils strongly bound B7x protein and inhibited the proliferation of both CD4 and CD8 T cells. These results suggest that host B7x may enable metastasizing cancer cells to escape local antitumor immune responses through interactions with the innate and adaptive immune systems. Thus, targeting the B7x pathway holds much promise for improving the efficacy of immunotherapy for metastatic cancer.

B7x (B7-H4 or B7S1) is the seventh member of the B7 family, and its in vivo function remains largely unknown. Despite new genetic data linking the B7x gene with autoimmune diseases, how exactly it contributes to peripheral tolerance and autoimmunity is unclear. In this study, we showed that B7x protein was not detected on APCs or T cells in both human and mice, which is unique in the B7 family. Because B7x protein is expressed in some peripheral cells such as pancreatic β cells, we used a CD8 T cell-mediated diabetes model (AI4αβ) in which CD8 T cells recognize an endogenous self-Ag, and found that mice lacking B7x developed more severe diabetes than control AI4αβ mice. Conversely, mice overexpressing B7x in the β cells (Rip-B7xAI4αβ) were diabetes free. Furthermore, adoptive transfer of effector AI4αβ CD8 T cells induced diabetes in control mice, but not in Rip-B7xAI4αβ mice. Mechanistic studies revealed that pathogenic effector CD8 T cells were capable of migrating to the pancreas but failed to robustly destroy tissue when encountering local B7x in Rip-B7xAI4αβ mice. Although AI4αβ CD8 T cells in Rip-B7xAI4αβ and AI4αβ mice showed similar cytotoxic function, cell death, and global gene expression profiles, these cells had greater proliferation in AI4αβ mice than in RIP-B7xAI4αβ mice. These results suggest that B7x in nonlymphoid organs prevents peripheral autoimmunity partially through inhibiting proliferation of tissue-specific CD8 T cells, and that local overexpression of B7x on pancreatic β cells is sufficient to abolish CD8 T cell-induced diabetes.

B7x (B7-H4 or B7S1), a member of the B7 family, inhibits in vitro T cell proliferation and cytokine production by binding to an unidentified receptor on activated T cells, but its in vivo function remains largely unclear. We show that B7x protein was expressed in epithelial cells of the lung, but not in lymphoid tissues. To investigate the role of B7x in the lung, we determined the susceptibility of B7x-deficient (B7x−/−) mice to a lethal pulmonary infection with Streptococcus pneumoniae. B7x−/−, but not B7-H3–deficient, mice were significantly more resistant to S. pneumoniae pulmonary infection than their wild-type (Wt) counterparts. B7x−/− mice had significantly lower bacterial burdens and levels of inflammatory cytokines in lungs as early as 12 h postinfection. They also had milder immunopathology that was localized in alveolar spaces, whereas Wt mice had severe inflammation that was perivascular. Control of infection in B7x−/− mice was associated with a marked increase in activated CD4 and CD8 T cells and fewer neutrophils in lungs, whereas the susceptible Wt mice had the opposite cellular profile. In B7x−/−Rag1−/− mice that lack T cells, reduction in bacterial burden was no longer observed. Control of S. pneumoniae and the increased survival observed was specific to the lung, because systemically infected B7x−/− mice were not resistant to infection. These data indicate that lung-expressed B7x negatively regulates T cells, and that in its absence, in B7x−/− mice, an enhanced T cell response contributed to reduced lethality in a pulmonary infection model with S. pneumoniae.

Methylation of histone H3 by Set1 and Set2 is required for deacetylation of nucleosomes in coding regions by histone deacetylase complexes (HDACs) Set3C and Rpd3C(S), respectively. We report that Set3C and Rpd3C(S) are co-transcriptionally recruited in the absence of Set1 and Set2, but in a manner stimulated by Pol II CTD kinase Cdk7/Kin28. Consistently, Rpd3C(S) and Set3C interact with Ser5-phosphorylated Pol II and histones in extracts, but only the histone interactions require H3 methylation. Moreover, reconstituted Rpd3C(S) binds specifically to Ser5-phosphorylated CTD peptides in vitro. Hence, whereas interaction with methylated H3 residues is required for Rpd3C(S) and Set3C deacetylation activities, their co-transcriptional recruitment is stimulated by the phosphorylated CTD. We further demonstrate that Rpd3, Hos2, and Hda1 have overlapping functions in deacetylating histones and suppressing co-transcriptional histone eviction. A strong correlation between increased acetylation and lower histone occupancy in HDA mutants implies that histone acetylation is a key determinant of nucleosome eviction.

Tlymphocytes of adaptive immunity provide vertebrates with the ability to survey for and respond specifically to an incredible diversity of antigens, whether foreign or native. Appropriate T cell response is required to eradicate pathogens, whereas abnormal T cell function could lead to autoimmune diseases, cancer, and transplantation rejection. The outcome of T cell engagement of antigen is determined by positive costimulation and negative coinhibition; both are primarily generated by the interaction between the B7 family and their receptor CD28 family (1). Recent years have seen the identification of several new members of B7/CD28 families. The growing B7 family now comprises seven members: B7-1 (CD80), B7-2 (CD86), B7h (CD275), PD-L1 (CD274), PD-L2 (CD273), B7-H3 (CD276), and B7x (B7-H4 or B7S1). Almost 5 years ago, we divided the B7 family into three groups by phylogenetic analysis: group I includes B7-1, B7-2, and B7h; group II consists of PD-L1 and PD-L2; and group III contains B7x and B7-H3 (2, 3). Receptors for group I are CD28, CTLA-4, and ICOS, and the receptor for group II is PD-1 (Fig. 1). B7-1 also binds PD-L1. One prediction of the phylogenetic comparison was that receptor(s) for B7-H3 would not be real homologue(s) of receptors for group I and II (3). Five years later, this prediction has been proven true (3). In this issue of PNAS, Hasiguchi et al. (3, 4) have identified one such receptor, triggering receptor expressed on myeloid cell (TREM)-like transcript 2 (TLT-2, or TREML2), which binds B7-H3 and costimulates activation of CD8 T cells in particular. TLT-2 is a member of the TREM receptor family (5, 6), which includes TREM-1, -2, and -3, as well as TLT-1 and -2. B7-H3 is the first ligand to be identified for the TREM … ¶To whom correspondence should be addressed. E-mail: xzang{at}aecom.yu.edu

SummaryT cell activity is controlled by a combination of antigen-dependent signaling through the T cell receptor and a set of auxiliary signals delivered through antigen-independent interactions, including the recognition of the B7 family of ligands. B7-H3 is a recently identified B7 family member that is strongly overexpressed in a range of cancers and correlates with poor prognosis. We report the crystal structure of murine B7-H3 at a 3 Å resolution, which provides a model for the organization of the IgV and IgC domains within the ectodomain. We demonstrate that B7-H3 inhibits T cell proliferation and show that the FG loop of the IgV domain plays a critical role in this function. B7-H3 crystallized as an unusual dimer arising from the exchange of the G strands in the IgV domains of partner molecules. This arrangement, in combination with previous reports, highlights the dynamic nature and plasticity of the immunoglobulin fold.