Hypoxia and hypoxia-inducible factor signals regulate the development, metabolism, and function of B cells

Epstein-Barr Virus-Driven B-Cell Transformation under Germinal Center Hypoxia Requires External Unsaturated Fatty Acids

Epstein-Barr virus (EBV) contributes to over 200,000 cancers annually, predominantly aggressive lymphomas originating from hypoxic germinal centers (< 1% O2). However, conventional models fail to recapitulate the physiologically relevant hypoxic microenvironment which profoundly influences B-cell metabolic remodeling during transformation. Here, we establish an ex vivo model of EBV-driven B-cell transformation under 1% O2, demonstrating robust transformation and super-enhancer activation of oncogenic regulators, including MYC. Multi-omic analyses reveal distinct metabolic adaptations to hypoxia. Unlike normoxic B-cells, which rely on fatty acid desaturases and oxidation to mitigate lipotoxicity, hypoxically transformed B-cells suppress fatty acid synthesis while upregulating glycerophospholipid metabolism and lipid droplet formation to buffer excess saturated lipids. Consequently, these cells exhibit heightened dependence on external unsaturated fatty acids to support proliferation. Our findings provide the first physiologically relevant ex vivo model of EBV-driven B-cell transformation under hypoxia, uncovering metabolic vulnerabilities that could inform targeted therapeutic strategies for EBV-associated malignancies.

Single cell transcriptome profiling of immune tissues from germ-free and specific pathogen-free piglet

The commensal microbiota provides immunomodulatory signals during the development, differentiation and activation of immune cells, and is crucial for maintaining host immune homeostasis. However, the systematic effects of commensal microbiota on host immunity based on large animal model at the single-cell level remain to be resolved. Here, we utilized single-cell RNA sequencing (scRNA-seq) to analyze the transcriptome profiling containing 57,720 cells from three important immune tissues [Peyer's patches (PP), mesenteric lymph node (MLN), and spleen] of germ-free (GF) and specific pathogen-free (SPF) piglet. We presented detailed description of the dataset and preliminarily identified the major cell types including immune and non-immune cells, and further annotated the immune cell subsets. This dataset provides a data mining resource for researchers involved in microbe-host interactions, and enables in-depth analysis of cell map alterations caused by the microbiota colonization during early immune development. As the first single-cell transcriptomics dataset for immune tissue of GF and SPF piglet, this provides a valuable data resource for the study of commensal microbe-host immunity regulation.

Immune Checkpoints in B Cells: Unlocking New Potentials in Cancer Treatment

B cells are crucial component of humoral immunity, and their role in the tumor immune microenvironment (TME) has garnered significant attention in recent years. These cells hold great potential and application prospects in the field of tumor immunotherapy. Research has demonstrated that the TME can remodel various B cell functions, including proliferation, differentiation, antigen presentation, and antibody production, thereby invalidating the anti-tumor effects of B cells. Concurrently, numerous immune checkpoints (ICs) on the surface of B cells are upregulated. Aberrant B-cell IC signals not only impair the function of B cells themselves, but also modulate the tumor-killing effects of other immune cells, ultimately fostering an immunosuppressive TME and facilitating tumor immune escape. Blocking ICs on B cells is beneficial for reversing the immunosuppressive TME and restoring anti-tumor immune responses. In this paper, the intricate connection between B-cell ICs and the TME is delved into, emphasizing the critical role of targeting B-cell ICs in anti-tumor immunity, which may provide valuable insights for the future development of tumor immunotherapy based on B cells.

Changes in immune cell populations during acclimatization to high altitude

The immune response to acute hypoxemia may play a critical role in high-altitude acclimatization and adaptation. However, if not properly controlled, hypoxemia-induced inflammation may exacerbate high-altitude pathologies, such as acute mountain sickness (AMS), or other hypoxia-related clinical conditions. Several studies report changes in immune cell subsets at high altitude. However, the mechanisms underlying these changes, and if these alterations are beneficial or maladaptive, remains unknown. To address this, we performed multiparameter flow cytometry on peripheral blood mononuclear cells (PBMCs) collected throughout 3 days of high-altitude acclimatization in healthy sea-level residents (n = 20). Additionally, we conducted in vitro stimulation assays to test if high-altitude hypoxia exposure influences responses of immune cells to subsequent inflammatory stimuli. We found several immune populations were altered at high altitude, including monocytes, T cells, and B cells. Some changes in immune cell populations are potentially correlated with AMS incidence and severity. In vitro high-altitude PBMC cultures stimulated with lipopolysaccharide (LPS) showed no changes in pro-inflammatory cytokine production after 1 day at high-altitude. However, by day three pro-inflammatory cytokine production in response to LPS decreased significantly. These results indicate that high-altitude exposure may initiate an inflammatory response that encompasses innate immune sensitization, with adaptive immune suppression following acclimatization.

Increased peritoneal B1-like cells during acute phase of human septic peritonitis

Sepsis is a life-threatening condition caused by dysregulated host responses to infection. Myeloid cell accumulation and lymphocyte decline are widely recognized phenomena in septic patients. However, the fate of specific immune cells remains unclear. Here, we report the results of a human explorative study of patients with septic peritonitis and patients undergoing abdominal surgery without sepsis. We analyzed pairwise peritoneal fluid and peripheral blood taken 24 h after surgery to characterize immediate immune cell changes. Our results show that myeloid cell expansion and lymphocyte loss occur in all patients undergoing open abdominal surgery, indicating that these changes are not specific to sepsis. However, B1-like lymphocytes were specifically increased in the peritoneal fluid of septic patients, correlating positively with sequential organ failure assessment (SOFA) and acute physiology and chronic health evaluation II (APACHE-II) clinical severity scores. In support of this notion, we identified an accumulation of peritoneal B1b lymphocytes in septic mice.

Circumventing B Cell Responses to Allow for Redosing of Adeno-Associated Virus Vectors

Adeno-associated virus (AAV)-mediated gene therapy has made significant progress in the last few decades. Nevertheless, challenges imposed by the immune system remain. The very high doses of AAV vectors used for some disorders have resulted in serious adverse events (SAEs) or even deaths, demonstrating that AAV vector doses that can safely be injected into patients are limited and for some indications below the therapeutic dose. Currently used immunosuppressive drugs have not prevented the SAEs, indicating that it may be prudent to treat patients with repeated transfer of moderate doses rather than a single injection of high doses of AAV vectors. The former approach has been avoided as AAV vectors elicit neutralizing antibodies that prevent successful reapplication of serologically crossreactive vectors. Immunosuppressive regimens that block B cell responses to AAV vectors or treatments that remove AAV neutralizing antibodies thus need to be developed to allow for a shift from toxic single-dose injections of AAV vectors to repeated treatments with more moderate and safe doses. Preventing or blocking antibody responses would also allow for redosing of patients with declining transgene product expression, or for effective AAV-mediated gene transfer into patients with the pre-existing neutralizing antibodies.

Hypoxic tumor microenvironment: Destroyer of natural killer cell function

In recent years, immunotherapy has made remarkable progress in treating certain tumors and hematological malignancies. However, the efficacy of natural killer (NK) cells, which are an important subset of innate lymphocytes used in anticancer immunotherapy, remains limited. Hypoxia, a critical characteristic of the tumor microenvironment (TME), is involved in tumor development and resistance to radiotherapy, chemotherapy, and immunotherapy. Moreover, hypoxia contributes to the impairment of NK cell function and may be a significant factor that limits their therapeutic effects. Targeted hypoxia therapy has emerged as a promising research area for enhancing the efficacy of NK cell therapy. Therefore, understanding how the hypoxic TME influences NK cell function is crucial for improving antitumor treatment outcomes.

Deficiency of factor-inhibiting HIF creates a tumor-promoting immune microenvironment

Hypoxia signaling influences tumor development through both cell-intrinsic and -extrinsic pathways. Inhibiting hypoxia-inducible factor (HIF) function has recently been approved as a cancer treatment strategy. Hence, it is important to understand how regulators of HIF may affect tumor growth under physiological conditions. Here we report that in aging mice factor-inhibiting HIF (FIH), one of the most studied negative regulators of HIF, is a haploinsufficient suppressor of spontaneous B cell lymphomas, particular pulmonary B cell lymphomas. FIH deficiency alters immune composition in aged mice and creates a tumor-supportive immune environment demonstrated in syngeneic mouse tumor models. Mechanistically, FIH-defective myeloid cells acquire tumor-supportive properties in response to signals secreted by cancer cells or produced in the tumor microenvironment with enhanced arginase expression and cytokine-directed migration. Together, these data demonstrate that under physiological conditions, FIH plays a key role in maintaining immune homeostasis and can suppress tumorigenesis through a cell-extrinsic pathway.

Metabolic imbalance driving immune cell phenotype switching in autoimmune disorders: Tipping the balance of T- and B-cell interactions

The interplay between the immune system and the metabolic state of a cell is intricate. In all phases of an immune response, the corresponding metabolic changes shall occur to support its modulation, in addition to the signalling through the cytokine environment and immune receptor stimulation. While autoimmune disorders may develop because of a metabolic imbalance that modulates switching between T-cell phenotypes, the effects that the interaction between T and B cells have on one another's cellular metabolism are yet to be understood in disease context. Here, we propose a perspective which highlights the potential of targeting metabolism to modulate T- and B-cell subtypes populations as well as T-B and B-T cell interactions to successfully treat autoimmune disorders. Specifically, we envision how metabolic changes can tip the balance of immune cells interactions, through definite mechanisms in both health and disease, to explain phenotype switches of B and T cells. Within this scenario, we highlight targeting metabolism that link inflammation, immunometabolism, epigenetics and ageing, is critical to understand inflammatory disorders. The combination of treatments targeting immune cells that cause (T/B) cell phenotype imbalances, and the metabolic pathways involved, may increase the effectiveness of treatment of autoimmune disorders, and/or ameliorate their symptoms to improve patients' quality of life.

Microbiota-dependent indole production stimulates the development of collagen-induced arthritis in mice

Altered tryptophan catabolism has been identified in inflammatory diseases like rheumatoid arthritis (RA) and spondyloarthritis (SpA), but the causal mechanisms linking tryptophan metabolites to disease are unknown. Using the collagen-induced arthritis (CIA) model, we identified alterations in tryptophan metabolism, and specifically indole, that correlated with disease. We demonstrated that both bacteria and dietary tryptophan were required for disease and that indole supplementation was sufficient to induce disease in their absence. When mice with CIA on a low-tryptophan diet were supplemented with indole, we observed significant increases in serum IL-6, TNF, and IL-1β; splenic RORγt+CD4+ T cells and ex vivo collagen-stimulated IL-17 production; and a pattern of anti-collagen antibody isotype switching and glycosylation that corresponded with increased complement fixation. IL-23 neutralization reduced disease severity in indole-induced CIA. Finally, exposure of human colonic lymphocytes to indole increased the expression of genes involved in IL-17 signaling and plasma cell activation. Altogether, we propose a mechanism by which intestinal dysbiosis during inflammatory arthritis results in altered tryptophan catabolism, leading to indole stimulation of arthritis development. Blockade of indole generation may present a unique therapeutic pathway for RA and SpA.

Microbiota-dependent indole production is required for the development of collagen-induced arthritis

Altered tryptophan catabolism has been identified in inflammatory diseases like rheumatoid arthritis (RA) and spondyloarthritis (SpA), but the causal mechanisms linking tryptophan metabolites to disease are unknown. Using the collagen-induced arthritis (CIA) model we identify alterations in tryptophan metabolism, and specifically indole, that correlate with disease. We demonstrate that both bacteria and dietary tryptophan are required for disease, and indole supplementation is sufficient to induce disease in their absence. When mice with CIA on a low-tryptophan diet were supplemented with indole, we observed significant increases in serum IL-6, TNF, and IL-1β; splenic RORγt+CD4+ T cells and ex vivo collagen-stimulated IL-17 production; and a pattern of anti-collagen antibody isotype switching and glycosylation that corresponded with increased complement fixation. IL-23 neutralization reduced disease severity in indole-induced CIA. Finally, exposure of human colon lymphocytes to indole increased expression of genes involved in IL-17 signaling and plasma cell activation. Altogether, we propose a mechanism by which intestinal dysbiosis during inflammatory arthritis results in altered tryptophan catabolism, leading to indole stimulation of arthritis development. Blockade of indole generation may present a novel therapeutic pathway for RA and SpA.

Crosstalk between hypoxic cellular micro-environment and the immune system: a potential therapeutic target for infectious diseases

There are overwhelming reports on the promotional effect of hypoxia on the malignant behavior of various forms of cancer cells. This has been proposed and tested exhaustively in the light of cancer immunotherapy. However, there could be more interesting functions of a hypoxic cellular micro-environment than malignancy. There is a highly intricate crosstalk between hypoxia inducible factor (HIF), a transcriptional factor produced during hypoxia, and nuclear factor kappa B (NF-κB) which has been well characterized in various immune cell types. This important crosstalk shares common activating and inhibitory stimuli, regulators, and molecular targets. Impaired hydroxylase activity contributes to the activation of HIFs. Inflammatory ligands activate NF-κB activity, which leads to the expression of inflammatory and anti-apoptotic genes. The eventual sequelae of the interaction between these two molecular players in immune cells, either bolstering or abrogating functions, is largely cell-type dependent. Importantly, this holds promise for interesting therapeutic interventions against several infectious diseases, as some HIF agonists have helped prevent immune-related diseases. Hypoxia and inflammation are common features of infectious diseases. Here, we highlighted the role of this crosstalk in the light of functional immunity against infection and inflammation, with special focus on various innate and adaptive immune cells. Particularly, we discussed the bidirectional effects of this crosstalk in the regulation of immune responses by monocytes/macrophages, dendritic cells, neutrophils, B cells, and T cells. We believe an advanced understanding of the interplay between HIFs and NF-kB could reveal novel therapeutic targets for various infectious diseases with limited treatment options.

Optimal AID expression and efficient immunoglobulin class switch recombination are dependent on the hypoxia-inducible factor

During immune responses, B cells engaging a cognate antigen are recruited to GCs in secondary lymphoid organs where they will diversify their BCR to generate highly specific and adapted humoral responses. They do so, by inducing the expression of activation-induced cytidine deaminase (AID), which initiates somatic hypermutation (SHM) and class switch recombination (CSR). AID deaminates cytosines in ss DNA, generating U:G mismatches that are processed to induce ds DNA break intermediates during CSR that result in the expression of a different antibody isotype. Interestingly, hypoxia regions have been reported in GCs and suggesting that hypoxia could modulate the humoral response. Furthermore, hypoxia inducible transcription factor (HIF) can bind to the AID promoter and induce AID expression in a non-B-cell setting, suggesting that it might be involved in the transcriptional induction of AID in B cells, hence, regulating SHM and CSR. We, thus, hypothesized that HIF could regulate the efficiency of CSR. Here, we show that the inactivation of both the HIF-1α and HIF-1β subunits of the HIF transcription factor in murine CH12 B cells results in defective CSR and that this is due to the suboptimal induction of AID expression.