IL-7-Induced Glycerol Transport and TAG Synthesis Promotes Memory CD8+ T Cell Longevity.

Memory T cells are critical for long-term immunity against reinfection and require interleukin-7 (IL-7), but the mechanisms by which IL-7 controls memory T cell survival, particularly metabolic fitness, remain elusive. We discover that IL-7 induces expression of the glycerol channel aquaporin 9 (AQP9) in virus-specific memory CD8+ T cells, but not naive cells, and that AQP9 is vitally required for their long-term survival. AQP9 deficiency impairs glycerol import into memory CD8+ T cells for fatty acid esterification and triglyceride (TAG) synthesis and storage. These defects can be rescued by ectopic expression of TAG synthases, which restores lipid stores and memory T cell survival. Finally, we find that TAG synthesis is a central component of IL-7-mediated survival of human and mouse memory CD8+T cells. This study uncovers the metabolic mechanisms by which IL-7 tailors the metabolism of memory T cells to promote their longevity and fast response to rechallenge.

The Interleukin-2-mTORc1 Kinase Axis Defines the Signaling, Differentiation, and Metabolism of T Helper 1 and Follicular B Helper T Cells.

The differentiation of CD4(+) helper T cell subsets with diverse effector functions is accompanied by changes in metabolism required to meet their bioenergetic demands. We find that follicular B helper T (Tfh) cells exhibited less proliferation, glycolysis, and mitochondrial respiration, accompanied by reduced mTOR kinase activity compared to T helper 1 (Th1) cells in response to acute viral infection. IL-2-mediated activation of the Akt kinase and mTORc1 signaling was both necessary and sufficient to shift differentiation away from Tfh cells, instead promoting that of Th1 cells. These findings were not the result of generalized signaling attenuation in Tfh cells, because they retained the ability to flux calcium and activate NFAT-transcription-factor-dependent cytokine production. These data identify the interleukin-2 (IL-2)-mTORc1 axis as a critical orchestrator of the reciprocal balance between Tfh and Th1 cell fates and their respective metabolic activities after acute viral infection.

Multi-Omics Characterization of Colon Mucosa and Submucosa/Wall from Crohn's Disease Patients.

Crohn's disease (CD) is a subtype of inflammatory bowel disease (IBD) characterized by transmural disease. The concept of transmural healing (TH) has been proposed as an indicator of deep clinical remission of CD and as a predictor of favorable treatment endpoints. Understanding the pathophysiology involved in transmural disease is critical to achieving these endpoints. However, most studies have focused on the intestinal mucosa, overlooking the contribution of the intestinal wall in Crohn's disease. Multi-omics approaches have provided new avenues for exploring the pathogenesis of Crohn's disease and identifying potential biomarkers. We aimed to use transcriptomic and proteomic technologies to compare immune and mesenchymal cell profiles and pathways in the mucosal and submucosa/wall compartments to better understand chronic refractory disease elements to achieve transmural healing. The results revealed similarities and differences in gene and protein expression profiles, metabolic mechanisms, and immune and non-immune pathways between these two compartments. Additionally, the identification of protein isoforms highlights the complex molecular mechanisms underlying this disease, such as decreased RTN4 isoforms (RTN4B2 and RTN4C) in the submucosa/wall, which may be related to the dysregulation of enteric neural processes. These findings have the potential to inform the development of novel therapeutic strategies to achieve TH.

Transcription factor STAT3 and type I interferons are corepressive insulators for differentiation of follicular helper and T helper 1 cells.

Follicular helper T (Tfh) cells are required for the establishment of T-dependent B cell memory and high affinity antibody-secreting cells. We have revealed herein opposing roles for signal transducer and activator of transcription 3 (STAT3) and type I interferon (IFN) signaling in the differentiation of Tfh cells following viral infection. STAT3-deficient CD4(+) T cells had a profound defect in Tfh cell differentiation, accompanied by decreased germinal center (GC) B cells and antigen-specific antibody production during acute infection with lymphocytic choriomeningitis virus. STAT3-deficient Tfh cells had strikingly increased expression of a number of IFN-inducible genes, in addition to enhanced T-bet synthesis, thus adopting a T helper 1 (Th1) cell-like effector phenotype. Conversely, IFN-αß receptor blockade restored Tfh and GC B cell phenotypes in mice containing STAT3-deficient CD4(+) T cells. These data suggest mutually repressive roles for STAT3 and type I IFN signaling pathways in the differentiation of Tfh cells following viral infection.

The transcription factor FoxO1 sustains expression of the inhibitory receptor PD-1 and survival of antiviral CD8(+) T cells during chronic infection.

Protein kinase B (also known as AKT) and the mechanistic target of rapamycin (mTOR) are central regulators of T cell differentiation, proliferation, metabolism, and survival. Here, we show that during chronic murine lymphocytic choriomeningitis virus infection, activation of AKT and mTOR are impaired in antiviral cytotoxic T lymphocytes (CTLs), resulting in enhanced activity of the transcription factor FoxO1. Blockade of inhibitory receptor programmed cell death protein 1 (PD-1) in vivo increased mTOR activity in virus-specific CTLs, and its therapeutic effects were abrogated by the mTOR inhibitor rapamycin. FoxO1 functioned as a transcriptional activator of PD-1 that promoted the differentiation of terminally exhausted CTLs. Importantly, FoxO1-null CTLs failed to persist and control chronic viral infection. Collectively, this study shows that CTLs adapt to persistent infection through a positive feedback pathway (PD-1?FoxO1?PD-1) that functions to both desensitize virus-specific CTLs to antigen and support their survival during chronic viral infection.

The interface between transcriptional and epigenetic control of effector and memory CD8⁺ T-cell differentiation.

Immunity to many intracellular pathogens requires the proliferation, differentiation, and function of CD8(+) cytotoxic T lymphocytes (CTLs). While the majority of effector CTLs die upon clearance of the pathogen, a small proportion of them survive to become long-lived memory CTLs. Memory CTLs can provide protective immunity against re-exposure to the same pathogen and are the principle motivation behind T-cell- based vaccine design. While a large body of cellular immunologic research has proven invaluable to define effector and memory CTLs by their different phenotypes and functions, an emerging focus in the field has been to understand how environmental cues regulate CTL differentiation on a genomic level. Genome-wide studies to profile transcriptional and epigenetic changes during infection have revealed that dynamic changes in DNA methylation patterns and histone modifications accompany transcriptional signatures that define and regulate CTL differentiation states. In this review, we emphasize the importance of epigenetic regulation of CD8(+) T-cell differentiation and the likely role that transcription factors play in this process.

A functional subset of CD8+ T cells during chronic exhaustion is defined by SIRPα expression.

Prolonged exposure of CD8+ T cells to antigenic stimulation, as in chronic viral infections, leads to a state of diminished function termed exhaustion. We now demonstrate that even during exhaustion there is a subset of functional CD8+ T cells defined by surface expression of SIRPα, a protein not previously reported on lymphocytes. On SIRPα+ CD8+ T cells, expression of co-inhibitory receptors is counterbalanced by expression of co-stimulatory receptors and it is only SIRPα+ cells that actively proliferate, transcribe IFNγ and show cytolytic activity. Furthermore, target cells that express the ligand for SIRPα, CD47, are more susceptible to CD8+ T cell-killing in vivo. SIRPα+ CD8+ T cells are evident in mice infected with Friend retrovirus, LCMV Clone 13, and in patients with chronic HCV infections. Furthermore, therapeutic blockade of PD-L1 to reinvigorate CD8+ T cells during chronic infection expands the cytotoxic subset of SIRPα+ CD8+ T cells.

Potent and conditional redirected T cell killing of tumor cells using Half DVD-Ig.

Novel biologics that redirect cytotoxic T lymphocytes (CTLs) to kill tumor cells bearing a tumor associated antigen hold great promise in the clinic. However, the ability to safely and potently target CD3 on CTL toward tumor associated antigens (TAA) expressed on tumor cells remains a challenge of both technology and biology. Herein we describe the use of a Half DVD-Ig format that can redirect CTL to kill tumor cells. Notably, Half DVD-Ig molecules that are monovalent for each specificity demonstrated reduced non-specific CTL activation and conditional CTL activation upon binding to TAA compared to intact tetravalent DVD-Ig molecules that are bivalent for each specificity, while maintaining good drug like properties and appropriate PK properties.

The transforming growth factor beta signaling pathway is critical for the formation of CD4 T follicular helper cells and isotype-switched antibody responses in the lung mucosa.

T follicular helper cells (Tfh) are crucial for the initiation and maintenance of germinal center (GC) reactions and high affinity, isotype-switched antibody responses. In this study, we demonstrate that direct TGF-ß signaling to CD4 T cells is important for the formation of influenza-specific Tfh cells, GC reactions, and development of isotype-switched, flu-specific antibody responses. Early during infection, TGF-ß signaling suppressed the expression of the high affinity IL-2 receptor α chain (CD25) on virus-specific CD4 T cells, which tempered IL-2 signaling and STAT5 and mammalian target of rapamycin (mTOR) activation in Tfh precursor CD4 T cells. Inhibition of mTOR allowed for the differentiation of Tfh cells in the absence of TGF-ßR signaling, suggesting that TGF-ß insulates Tfh progenitor cells from IL-2-delivered mTOR signals, thereby promoting Tfh differentiation during acute viral infection. These findings identify a new pathway critical for the generation of Tfh cells and humoral responses during respiratory viral infections.

Prostaglandin E2 and programmed cell death 1 signaling coordinately impair CTL function and survival during chronic viral infection.

More than 10% of the world's population is chronically infected with HIV, hepatitis C virus (HCV) or hepatitis B virus (HBV), all of which can cause severe disease and death. These viruses persist in part because continuous antigenic stimulation causes the deterioration of virus-specific cytotoxic T lymphocyte (CTL) function and survival. Additionally, antiviral CTLs autonomously suppress their responses to limit immunopathology by upregulating inhibitory receptors such as programmed cell death 1 (PD-1). Identification and blockade of the pathways that induce CTL dysfunction may facilitate the clearance of chronic viral infections. We found that the prostaglandin E2 (PGE2) receptors EP2 and EP4 were upregulated on virus-specific CTLs during chronic lymphocytic choriomeningitis virus (LCMV) infection and suppressed CTL survival and function. We show that the combined blockade of PGE2 and PD-1 signaling was therapeutic in terms of improving viral control and augmenting the numbers of functional virus-specific CTLs. Thus, PGE2 inhibition is both an independent candidate therapeutic target and a promising adjunct therapy to PD-1 blockade for the treatment of HIV and other chronic viral infections.

Chronic viral infection promotes sustained Th1-derived immunoregulatory IL-10 via BLIMP-1.

During the course of many chronic viral infections, the antiviral T cell response becomes attenuated through a process that is regulated in part by the host. While elevated expression of the immunosuppressive cytokine IL-10 is involved in the suppression of viral-specific T cell responses, the relevant cellular sources of IL-10, as well as the pathways responsible for IL-10 induction, remain unclear. In this study, we traced IL-10 production over the course of chronic lymphocytic choriomeningitis virus (LCMV) infection in an IL-10 reporter mouse line. Using this model, we demonstrated that virus-specific T cells with reduced inflammatory function, particularly Th1 cells, display elevated and sustained IL-10 expression during chronic LCMV infection. Furthermore, ablation of IL-10 from the T cell compartment partially restored T cell function and reduced viral loads in LCMV-infected animals. We found that viral persistence is needed for sustained IL-10 production by Th1 cells and that the transcription factor BLIMP-1 is required for IL-10 expression by Th1 cells. Restimulation of Th1 cells from LCMV-infected mice promoted BLIMP-1 and subsequent IL-10 expression, suggesting that constant antigen exposure likely induces the BLIMP-1/IL-10 pathway during chronic viral infection. Together, these data indicate that effector T cells self-limit their responsiveness during persistent viral infection via an IL-10-dependent negative feedback loop.