Dass S. Vinay

Differences in Gastric Carcinoma Microenvironment Stratify According to EBV Infection Intensity: Implications for Possible Immune Adjuvant Therapy

Epstein-Barr virus (EBV) is associated with roughly 10% of gastric carcinomas worldwide (EBVaGC). Although previous investigations provide a strong link between EBV and gastric carcinomas, these studies were performed using selected EBV gene probes. Using a cohort of gastric carcinoma RNA-seq data sets from The Cancer Genome Atlas (TCGA), we performed a quantitative and global assessment of EBV gene expression in gastric carcinomas and assessed EBV associated cellular pathway alterations. EBV transcripts were detected in 17% of samples but these samples varied significantly in EBV coverage depth. In four samples with the highest EBV coverage (hiEBVaGC – high EBV associated gastric carcinoma), transcripts from the BamHI A region comprised the majority of EBV reads. Expression of LMP2, and to a lesser extent, LMP1 were also observed as was evidence of abortive lytic replication. Analysis of cellular gene expression indicated significant immune cell infiltration and a predominant IFNG response in samples expressing high levels of EBV transcripts relative to samples expressing low or no EBV transcripts. Despite the apparent immune cell infiltration, high levels of the cytotoxic T-cell (CTL) and natural killer (NK) cell inhibitor, IDO1, was observed in the hiEBVaGCs samples suggesting an active tolerance inducing pathway in this subgroup. These results were confirmed in a separate cohort of 21 Vietnamese gastric carcinoma samples using qRT-PCR and on tissue samples using in situ hybridization and immunohistochemistry. Lastly, a panel of tumor suppressors and candidate oncogenes were expressed at lower levels in hiEBVaGC versus EBV-low and EBV-negative gastric cancers suggesting the direct regulation of tumor pathways by EBV.

4-1BB Triggering Ameliorates Experimental Autoimmune Encephalomyelitis by Modulating the Balance between Th17 and Regulatory T Cells

Agonistic anti–4-1BB Ab is known to ameliorate experimental autoimmune encephalomyelitis. 4-1BB triggering typically leads to the expansion of CD8+ T cells, which produce abundant IFN-γ, and this in turn results in IDO-dependent suppression of autoimmune responses. However, because neutralization of IFN-γ or depletion of CD8+ T cell only partially abrogates the effect of 4-1BB triggering, we sought to identify an additional mechanism of 4-1BB–triggered suppression of autoimmune responses using IFN-γ- or IFN-γR–deficient mice. 4-1BB triggering inhibited the generation of Th17 cells that is responsible for experimental autoimmune encephalomyelitis induction and progression, and increased Foxp3+CD4+ regulatory T (Treg) cells, particularly among CD4+ T cells. This was not due to a direct effect of 4-1BB signaling on CD4+ T cell differentiation: 4-1BB signaling not only reduced Th17 cells and increased Treg cells in wild-type mice, which could be due to IFN-γ production by the CD8+ T cells, but also did so in IFN-γ–deficient mice, in that case by downregulating IL-6 production. These results show that although secondary suppressive mechanisms evoked by 4-1BB triggering are usually masked by the strong effects of IFN-γ, 4-1BB signaling seems to modulate autoimmune responses by a number of mechanisms, and modulation of the Th17 versus Treg cell balance is one of those mechanisms.

TNF superfamily: costimulation and clinical applications.

The molecules concerned with costimulation belong either to the immunoglobulin (Ig) or tumor necrosis factor (TNF) superfamily. The tumor necrosis superfamily comprises molecules capable of providing both costimulation and cell death. In this review we briefly summarize certain TNF superfamily receptor–ligand pairs that are endowed with costimulatory properties and their importance in health and disease.

Targeting TNF superfamily members for therapeutic intervention in rheumatoid arthritis

Rheumatoid arthritis (RA) is an inflammatory disease is one of the most serious medical problems, affecting ∼1% of all people worldwide, irrespective of race. The disease is autoimmune in nature and characterized by chronic inflammation of the synovial tissues in multiple joints that leads to joint destruction. Although T cells are central players in RA development, B cells are required for full penetrance of disease largely via their production of autoantibodies against Fc domain of IgG rheumatoid factor (RF). Treatment options for RA are limited and if any, are inadequate due to associated side effects. Members of the tumor necrosis factor (TNF) superfamily play important roles in a number of autoimmune diseases, including RA. In this review, we briefly summarize key features of the superfamily, we will consider how the well-characterized members concerned with immune regulation are coordinated and their roles in rheumatoid arthritis.

Origins and functional basis of regulatory CD11c+CD8+ T cells

Previously, we showed that CD11c defines a novel subset of CD8+ T cells whose in vivo activity is therapeutic for arthritis; however, the mechanisms directing their development, identity of their precursors, and basis of their effector function remain unknown. Here, we show that the novel subset develops from CD11csurface−CD8+ T cells and undergoes robust expansion in an antigen‐ and 4‐1BB (CD137)‐dependent manner. CD11c+CD8+ T cells exist in naïve mice (<3%) with limited suppressive activity. Once activated, they suppress CD4+ T cells in vivo and in vitro. Suppression of CD4+ by CD11c+CD8+ T cells is related to an increase in IDO activity induced in competent cells via the general control non‐derepressible‐2 pathway. CD11c+CD8+ T cells are refractory to the effect of IDO but constrict in a novel 1‐methyl D,L‐tryptophan‐dependent mechanism resulting in reversal of their suppressive effects. Thus, our data uncover, for the first time, the origin, development, and basis of the suppressive function of this novel CD11c+CD8+ T‐cell subpopulation that has many signature features of Treg.

PDCA Expression by B Lymphocytes Reveals Important Functional Attributes

We have demonstrated in this study the existence of a PDCA-expressing functional B cell population (PDCA+ B lymphocytes), which differentiates from activated conventional B (PDCA−IgM+) lymphocytes. Stimulation with anti-μ, LPS, CpG oligodeoxynucleotide, HSV-1, or CTLA-4 Ig activates the PDCA+ B lymphocytes, leading to cell division and induction of type I IFNs and IDO. Notably, the PDCA+ B lymphocytes are capable of Ag-specific Ab production and Ig class switching, which is corroborated by transfer experiments in B- and PDCA+ B lymphocyte-deficient μMT mice. Importantly, in lupus-prone MRL-Faslpr mice, PDCA+ B lymphocytes remain the principal source of autoantibodies. The PDCA+ B lymphocytes have phenotypes with plasmacytoid dendritic cells, but are a distinct cell population in that they develop from C-kit+B220+ pro-B precursors. Thus, our data suggest that not all PDCA+ cells are dendritic cell-derived plasmacytoid dendritic cells and that a significant majority is the PDCA+ B lymphocyte population having distinct phenotype and function.

CD11c+CD8+ T cells: Two-faced adaptive immune regulators

Regulatory cells, important controllers of immune homeostasis, carry out a multi-pronged attack by deleting overactive pathogenic immune cells, by supporting anergy, and by blocking effector functions, thereby contributing to the amelioration of disease. CD8+ T cells co-expressing CD11c are a new addition to the growing list of regulatory cells. Naïve mice harbor CD11c-expressing CD8+ T cells (<3%) that expand further in an antigen-dependent manner. Although activated CD11c+CD8+ T cells express suppressive cytokines such as IL-10 and TGF-beta, their production of IFN-gamma is central to their immune suppressive potential. The CD11c+CD8+ T cells target pathogenic CD4+ T cells in a cell-cell contact dependent manner via IDO- and GCN2-dependent mechanisms. Adoptive transfer of activated CD11c+CD8+ T cells halts the progression of autoimmune rheumatoid arthritis and colitis. However, in certain virus and cancer models the CD11c+CD8+ T cells assume the role of immune effectors, boosting immune potential. This seemingly dual nature of these cells--exerting regulatory vs. effector activities--makes them an attractive therapeutic target. In this review, we discuss the discovery, origins and developmental requirements of CD11c+CD8+cells, and the basis of their immuno-suppressive and effector potentials.

4–1BB signal stimulates the activation, expansion, and effector functions of γδ T cells in mice and humans

We show here that the expression of 4–1BB is rapidly induced in γδ T cells following antigenic stimulation in both mice and humans, and ligation of the newly acquired 4–1BB with an agonistic anti‐4–1BB augments cell division and cytokine production. We further demonstrate that γδ rather than αβ T cells protect mice from Listeria monocytogenes (LM) infection and 4–1BB stimulation enhances the γδ T‐cell activities in the acute phase of LM infection. IFN‐γ produced from γδ T cells was the major soluble factor regulating LM infection. Vγ1+ T cells were expanded in LM‐infected mice and 4–1BB signal triggered an exclusive expansion of Vγ1+ T cells and induced IFN‐γ in these Vγ1+ T cells. Similarly, 4–1BB was induced on human γδ T cells and shown to be fully functional. Combination treatment with human γδ T cells and anti‐hu4–1BB effectively protected against LM infection in human γδ T cell‐transferred NOD‐SCID mice. Taken together, these data provide evidence that the 4–1BB signal is an important regulator of γδ T cells and induces robust host defense against LM infection.

Exposure of a distinct PDCA-1+ (CD317) B cell population to agonistic anti-4-1BB (CD137) inhibits T and B cell responses both in vitro and in vivo.

4-1BB (CD137) is an important T cell activating molecule. Here we report that it also promotes development of a distinct B cell subpopulation co-expressing PDCA-1. 4-1BB is expressed constitutively, and its expression is increased when PDCA-1+ B cells are activated. We found that despite a high level of surface expression of 4-1BB on PDCA-1+ B cells, treatment of these cells with agonistic anti-4-1BB mAb stimulated the expression of only a few activation markers (B7-2, MHC II, PD-L2), cytokines (IL-12p40/p70), and chemokines (MCP-1, RANTES), as well as sTNFR1, and the immunosuppressive enzyme, IDO. Although the PDCA-1+ B cells stimulated by anti-4-1BB expressed MHC II at high levels and took up antigens efficiently, Ig class switching was inhibited when they were pulsed with T-independent (TI) or T-dependent (TD) Ags and adoptively transferred into syngeneic recipients. Furthermore, when anti-4-1BB-treated PDCA-1+ B cells were pulsed with OVA peptide and combined with Vα2+CD4+ T cells, Ag-specific cell division was inhibited both in vitro and in vivo. Our findings suggest that the 4-1BB signal transforms PDCA-1+ B cells into propagators of negative immune regulation, and establish an important role for 4-1BB in PDCA-1+ B cell development and function.

Therapeutic potential of anti-CD137 (4-1BB) monoclonal antibodies

Introduction: 4-1BB (CD137) is an important T-cell stimulating molecule. The 4-1BB mAb or its variants have shown remarkable therapeutic activity against autoimmunity, viral infections, and cancer. Antibodies to 4-1BB have recently entered clinical trials for the treatment of cancer with favorable toxicity profile. In this article, we present a review documenting the efficacy and pitfalls of 4-1BB therapy. Areas covered: An extensive literature search has been made on 4-1BB, spanning two decades, and a comprehensive report is presented here highlighting the origins, biological effects, therapeutic potential, and mechanistic basis of targeting 4-1BB as well as the side effects associated with such therapy. Expert opinion: Research so far indicates that 4-1BB is highly protective against various pathological conditions including cancer. However, a few important side effects of 4-1BB therapy such as liver toxicity, thrombocytopenia, anemia, and suppressive effects on certain immune competent cells should be taken into consideration before it is used for human therapy.