Regulation of immune responses by L-arginine metabolism

Tumor-Released Products Promote Bone Marrow-Derived Macrophage Survival and Proliferation

Macrophages play a central role within the tumor microenvironment, with relevant implications for tumor progression. The modulation of their phenotype is one of the mechanisms used by tumors to escape from effective immune responses. This study was designed to analyze the influence of soluble products released by tumors, here represented by the tumor-conditioned media of two tumor cell lines (3LL from Lewis lung carcinoma and MN/MCA from fibrosarcoma), on murine macrophage differentiation and polarization in vitro. Data revealed that tumor-conditioned media stimulated macrophage differentiation but influenced the expression levels of macrophage polarization markers, cytokine production, and microRNAs of relevance for macrophage biology. Interestingly, tumor-derived soluble products supported the survival and proliferation rate of bone marrow precursor cells, an effect observed even with mature macrophages in the presence of M2 but not M1 inducers. Despite presenting low concentrations of macrophage colony-stimulating factor (M-CSF), tumor-conditioned media alone also supported the proliferation of cells to a similar extent as exogenous M-CSF. This effect was only evident in cells positive for the expression of the M-CSF receptor (CD115) and occurred preferentially within the CD16⁺ subset. Blocking CD115 partially reversed the effect on proliferation. These results suggest that tumors release soluble products that not only promote macrophage development from bone marrow precursors but also stimulate the proliferation of cells with specific phenotypes that could support protumoral functions.

Bias of the Immune Response to Pneumocystis murina Does Not Alter the Ability of Neonatal Mice to Clear the Infection

Newborn mice are unable to clear Pneumocystis (PC) infection with the same efficiency as adults due, in part, to their inability to develop a robust immune response to infection until three weeks of age. It is known that infants tend develop a Th2 skewed response to antigen so we sought to determine whether a biased cytokine response altered the clearance of PC infection in neonatal mice. P. murina infection in neonatal mice resulted in increased IL-4 expression by CD4 T cells and myeloid cells, augmented IL-13 secretion within the airways and increased arginase activity in the airways, indicative of Th2-type responses. P. murina-infected IL-4Rα^-/- neonates had a shift towards Th1 cytokine production and increased numbers of CD4 and CD8 T cells within the lung as well as elevated levels of P. murina-specific IgG. IFNγ^-/- and IL-23 p19^-/- mice had altered CD4-T cell-dependent cytokine and cell responses. Though we could alter the T helper cell environment in neonatal knockout mice, there was no loss in the ability of these pups to clear infection. It is possible that the Th2 phenotype normally seen in neonatal mice protects the developing lung from pro-inflammatory immune responses without compromising host defense against P. murina.

Rational Design of Immunomodulatory Hydrogels for Chronic Wound Healing

With all the advances in tissue engineering for construction of fully functional skin tissue, complete regeneration of chronic wounds is still challenging. Since immune reaction to the tissue damage is critical in regulating both the quality and duration of chronic wound healing cascade, strategies to modulate the immune system are of importance. Generally, in response to an injury, macrophages switch from pro-inflammatory to an anti-inflammatory phenotype. Therefore, controlling macrophages' polarization has become an appealing approach in regenerative medicine. Recently, hydrogels-based constructs, incorporated with various cellular and molecular signals, have been developed and utilized to adjust immune cell functions in various stages of wound healing. Here, the current state of knowledge on immune cell functions during skin tissue regeneration is first discussed. Recent advanced technologies used to design immunomodulatory hydrogels for controlling macrophages' polarization are then summarized. Rational design of hydrogels for providing controlled immune stimulation via hydrogel chemistry and surface modification, as well as incorporation of cell and molecules, are also dicussed. In addition, the effects of hydrogels' properties on immunogenic features and the wound healing process are summarized. Finally, future directions and upcoming research strategies to control immune responses during chronic wound healing are highlighted.

Nanoparticles Targeting Innate Immune Cells in Tumor Microenvironment

A variety of innate immune cells such as macrophages, dendritic cells, myeloid-derived suppressor cells, natural killer cells, and neutrophils in the tumor microenvironments, contribute to tumor progression. However, while several recent reports have studied the use of immune checkpoint-based cancer immunotherapy, little work has focused on modulating the innate immune cells. This review focuses on the recent studies and challenges of using nanoparticles to target innate immune cells. In particular, we also examine the immunosuppressive properties of certain innate immune cells that limit clinical benefits. Understanding the cross-talk between tumors and innate immune cells could contribute to the development of strategies for manipulating the nanoparticles targeting tumor microenvironments.

Myeloid-Derived Suppressor Cells in Trypanosoma cruzi Infection

Myeloid-derived suppressor cells (MDSCs) are immature heterogeneous myeloid cells that expand in pathologic conditions as cancer, trauma, and infection. Although characterization of MDSCs is continuously revisited, the best feature is their suppressor activity. There are many markers for MDSC identification, it is distinctive that they express inducible nitric oxide synthase (iNOS) and arginase 1, which can mediate immune suppression. MDSCs can have a medullary origin as a result of emergency myelopoiesis, but also can have an extramedullary origin. Early studies on Trypanosoma cruzi infection showed severe immunosuppression, and several mechanisms involving parasite antigens and host cell mediators were described as inhibition of IL-2 and IL-2R. Another mechanism of immunosuppression involving tumor necrosis factor/interferon γ-dependent nitric oxide production by inducible nitric oxide synthase was also described. Moreover, other studies showed that nitric oxide was produced by CD11b⁺ Gr-1⁺ MDSCs in the spleen, and later iNOS and arginase 1 expressed in CD11b⁺Ly6C⁺Ly6G^lo monocytic MDSC were found in spleen and heart of T. cruzi infected mice that suppressed T cell proliferation. Uncontrolled expansion of monocytic MDSCs leads to L-arginine depletion which hinders nitric oxide production leading to death. Supplement of L-arginine partially reverts L-arginine depletion and survival, suggesting that L-arginine could be administered along with anti-parasitical drugs. On the other hand, pharmacological inhibition of MDSCs leads to death in mice, suggesting that some expansion of MDSCs is needed for an efficient immune response. The role of signaling molecules mediating immune suppression as reactive oxygen species, reactive nitrogen species, as well as prostaglandin E2, characteristics of MDSCs, in T. cruzi infection is not fully understood. We review and discuss the role of these reactive species mediators produced by MDSCs. Finally, we discuss the latest results that link the SLAMF1 immune receptor with reactive oxygen species. Interaction of the parasite with the SLAMF1 modulates parasite virulence through myeloid cell infectivity and reactive oxygen species production. We discuss the possible strategies for targeting MDSCs and SLAMF1 receptor in acute Trypanosoma cruzi infection in mice, to evaluate a possible translational application in human acute infections.

Cutting edge: Metabolic immune reprogramming, reactive oxygen species, and cancer

A recently proposed term "immunometabolism" points to the functional intracellular metabolic changes that occur within different immune cells. Recent findings suggest that immune responses can be determined by the metabolic status of immune cells and metabolic reprogramming is an important feature of immune cell activation. Metabolic reprogramming is also well known for cancer cells and has been suggested as a major sign of cancer progression. Metabolic reprogramming of immune cells is also seen in the tumor microenvironment. In the past decade, immunometabolism has progressively become an extraordinarily vibrant and productive area of study in immunology because of its importance for immunotherapy. Understanding the immunometabolic situation of T cells and other immune cells along with the metabolic behavior of cancer cells can help us design new therapeutic approaches against cancers. Here, we have the aim to review the cutting-edge findings on the immunometabolic situation in immune and tumor cells. We discuss new findings on signaling pathways during metabolic reprogramming, its regulation, and the participation of reactive oxygen species in these processes.

GB1275, a first-in-class CD11b modulator: rationale for immunotherapeutic combinations in solid tumors

Resistance to immune checkpoint inhibitors (ICI) and other anticancer therapies is often associated with the accumulation of myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) in the tumor microenvironment (TME). Therefore, targeting MDSC recruitment or function is of significant interest as a strategy to treat patients with ICI-resistant cancer. The migration and recruitment of MDSCs to the TME is mediated in part by the CD11b/CD18 integrin heterodimer (Mac-1; α_Mβ₂), expressed on both MDSCs and TAMs. However, inhibition or blockade of CD11b/CD18 has had limited success in clinical trials to date, likely since saturation of CD11b requires doses that are not clinically tolerable with the agents tested so far. Interestingly, activation of CD11b with leukadherin-1 was found to reduce macrophage and neutrophil migration in animal models of inflammatory conditions. Preclinical studies with GB1275, a salt form of leukadherin-1, demonstrated that activation of CD11b improves the antitumor immune response and enhances the response to immunotherapy in mouse models of pancreatic adenocarcinoma, breast cancer and lung cancer. Based on the promising results from preclinical studies, a phase 1/2 clinical study (NCT04060342) of GB1275 in patients with advanced solid tumor types known to be resistant or less likely responsive to immuno-oncology therapies, including pancreatic, breast, prostate, and microsatellite-stable colorectal cancer, is ongoing. In this review, we examine targeting MDSCs as a therapeutic approach in cancer therapy, with a special focus on GB1275 preclinical studies laying the rationale for the phase 1/2 clinical study.

Immune-metabolic interactions between Leishmania and macrophage host

Manipulation of host metabolic fluxes by Leishmania represents a strategy to circumvent host immune response leading to long-term parasite survival and playing an important role in the pathology of infection. Specific Leishmania-dependent metabolic alterations in infected macrophages have been associated with resistance or susceptibility to infection. Thus, deciphering the multilevel interactions between metabolism and function on innate immune cells during infection offers considerable therapeutic or prophylactic promise. In this review, we provide an overview of recent literature highlighting Leishmania-macrophage interactions and discuss the potential of metabolic targeted therapies to shift the balance of dysfunctional, damaging, or non-productive responses to protective immune reactivity patterns towards pathogen elimination.

Gut microbiome-mediated metabolism effects on immunity in rural and urban African populations

The human gut microbiota is increasingly recognized as an important factor in modulating innate and adaptive immunity through release of ligands and metabolites that translocate into circulation. Urbanizing African populations harbor large intestinal diversity due to a range of lifestyles, providing the necessary variation to gauge immunomodulatory factors. Here, we uncover a gradient of intestinal microbial compositions from rural through urban Tanzanian, towards European samples, manifested both in relative abundance and genomic variation observed in stool metagenomics. The rural population shows increased Bacteroidetes, led by Prevotella copri, but also presence of fungi. Measured ex vivo cytokine responses were significantly associated with 34 immunomodulatory microbes, which have a larger impact on circulating metabolites than non-significant microbes. Pathway effects on cytokines, notably TNF-α and IFN-γ, differential metabolome analysis and enzyme copy number enrichment converge on histidine and arginine metabolism as potential immunomodulatory pathways mediated by Bifidobacterium longum and Akkermansia muciniphila.

The authors profile stool metagenomics and plasma metabolomics in Tanzanian individuals and uncover a gradient of gut microbial profiles, from rural through urban Tanzania towards Western populations. Integration with ex vivo blood microbial stimulations reveals immune responses associated with histidine and arginine pathways, mediated by Bifidobacterium longum and Akkermansia muciniphila.

Sevoflurane preconditioning protects experimental ischemic stroke by enhancing anti-inflammatory microglia/macrophages phenotype polarization through GSK-3β/Nrf2 pathway

Aims

Sevoflurane preconditioning (SPC) results in cerebral ischemic tolerance; however, the mechanism remains unclear. Promoting microglia/macrophages polarization from pro‐inflammatory state to anti‐inflammatory phenotype has been indicated as a potential treatment target against ischemic stroke. In this study, we aimed to assess the effect of SPC on microglia polarization after stroke and which signaling pathway was involved in this transition.

Methods

Mouse primary microglia with SPC were challenged by oxygen‐glucose deprivation (OGD) or lipopolysaccharide (LPS), and mice with SPC were subjected to middle cerebral artery occlusion (MCAO). Then, the mRNA and protein levels of pro‐inflammatory/anti‐inflammatory factors were analyzed. GSK‐3β phosphorylation and Nrf2 nuclear translocation were measured. The mRNA and protein expression of pro‐inflammatory/anti‐inflammatory factors, neurological scores, infarct volume, cellular apoptosis, the proportion of pro‐inflammatory/anti‐inflammatory microglia/macrophages, and the generation of super‐oxidants were examined after SPC or GSK‐3β inhibitor TDZD treatment with or without Nrf2 deficiency.

Results

Sevoflurane preconditioning promoted anti‐inflammatory and inhibited pro‐inflammatory microglia/macrophages phenotype both in vitro and in vivo. GSK‐3β phosphorylation at Ser9 was increased after SPC. Both SPC and TDZD administration enhanced Nrf2 nuclear translocation, reduced pro‐inflammatory microglia/macrophages markers expression, promoted anti‐inflammatory markers level, and elicited a neuroprotective effect. Nrf2 deficiency abolished the promoted anti‐inflammatory microglia/macrophages polarization and ischemic tolerance induced by TDZD treatment. The reduced percentage of pro‐inflammatory positive cells and super‐oxidants generation induced by SFC or TDZD was also reversed by Nrf2 knockdown.

Conclusions

Our results indicated that SPC exerts brain ischemic tolerance and promotes anti‐inflammatory microglia/macrophages polarization by GSK‐3β‐dependent Nrf2 activation, which provides a novel mechanism for SPC‐induced neuroprotection.

Decoding the Myeloid-Derived Suppressor Cells in Lymphoid Malignancies

Myeloid-derived suppressor cells (MDSCs) are immature myeloid precursors which emerged as a potent regulator of the immune system, exerting suppressive properties in diverse disease settings. In regards to cancer, MDSCs have an established role in solid tumors; however, their contribution to immune regulation during hematologic malignancies and particularly in lymphomas remains ill-defined. Herein focused on lymphoma, we discuss the literature on MDSC cells in all histologic types, and we also refer to lessons learned by animal models of lymphoma. Furthermore, we elaborate on future directions and unmet needs and challenges in the MDSC field related to lymphoma malignancies which may shed light on the complex nature of the immune system in malignancies.

Plasma amino acid levels in individuals with bacterial pneumonia and healthy controls

BACKGROUND & AIMS

Amino acids play an important role in immune responses and as neurotransmitters. During the course of a bacterial pneumonia episode, from the onset to the recovery phase, immune responses dramatically change, as does the metabolism of amino acids, a concept referred to as immuno-nutrition. We investigated the differences in plasma amino acid levels (PAA) between the acute and recovery phases in individuals with community-acquired pneumonia (CAP) and healthy controls.

METHODS

Two groups of participants were recruited: Healthy adults aged over 60 years and patients hospitalized with CAP. Samples were collected on Day 0 (the day of admission) and Day 7 (after 6-8 days treatment).

RESULTS

A total of 93 healthy adults and 60 patients with CAP participated in the study. Of those with CAP, 43 had their amino acids measured on Day 7. Patients with CAP had markedly decreased PAA of 12 amino acids on Day 0. Citrulline, histidine, and tryptophan remained low in male, while aspartic acid, asparagine, ornithine, proline, and threonine were higher on Day 7 in both males and females. Phenylalanine increased at Day 0 and Day7.

CONCLUSIONS

The findings suggest that the host response against bacterial infection changed the plasma amino acid levels. PAA on Day 7 (representing convalescence) continued to display an amino acid profile distinct from that observed in healthy individuals. Based on these findings, reconsideration for providing amino acids to patients with bacterial pneumonia should be needed depending on stage of the pneumonia from the perspective of immuno-nutrition.

Severe COVID-19: Immunosuppression or Hyperinflammation?

ABSTRACT

The ongoing coronavirus disease 2019 (COVID-19) pandemic has swept over the world and causes thousands of deaths. Although the clinical features of COVID-19 become much clearer than before, there are still further problems with the pathophysiological process and treatments of severe patients. One primary problem is with the paradoxical immune states in severe patients with COVID-19. Studies indicate that Severe Acute Respiratory Syndrome Coronavirus 2 can attack the immune system, manifested as a state of immunosuppression with a decrease in lymphocytes, whereas a state of hyperinflammation, presenting as elevated cytokine levels, is also detected in COVID-19. Therefore, discussing the specific status of immunity in COVID-19 will contribute to the understanding of its pathophysiology and the search for appropriate treatments. Here, we review all the available literature concerning the different immune states in COVID-19 and the underlying pathophysiological mechanisms. In addition, the association between immune states and the development and severity of disease as well as the impact on the selection of immunotherapy strategies are discussed in our review.

Could metabolomics drive the fate of COVID-19 pandemic? A narrative review on lights and shadows

Human Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2) infection activates a complex interaction host/virus, leading to the reprogramming of the host metabolism aimed at the energy supply for viral replication. Alterations of the host metabolic homeostasis strongly influence the immune response to SARS-CoV-2, forming the basis of a wide range of outcomes, from the asymptomatic infection to the onset of COVID-19 and up to life-threatening acute respiratory distress syndrome, vascular dysfunction, multiple organ failure, and death. Deciphering the molecular mechanisms associated with the individual susceptibility to SARS-CoV-2 infection calls for a system biology approach; this strategy can address multiple goals, including which patients will respond effectively to the therapeutic treatment. The power of metabolomics lies in the ability to recognize endogenous and exogenous metabolites within a biological sample, measuring their concentration, and identifying perturbations of biochemical pathways associated with qualitative and quantitative metabolic changes. Over the last year, a limited number of metabolomics- and lipidomics-based clinical studies in COVID-19 patients have been published and are discussed in this review. Remarkable alterations in the lipid and amino acid metabolism depict the molecular phenotype of subjects infected by SARS-CoV-2; notably, structural and functional data on the lipids-virus interaction may open new perspectives on targeted therapeutic interventions. Several limitations affect most metabolomics-based studies, slowing the routine application of metabolomics. However, moving metabolomics from bench to bedside cannot imply the mere determination of a given metabolite panel; rather, slotting metabolomics into clinical practice requires the conversion of metabolic patient-specific data into actionable clinical applications.

Revisiting the Mechanisms of Immune Evasion Employed by Human Parasites

For the establishment of a successful infection, i.e., long-term parasitism and a complete life cycle, parasites use various diverse mechanisms and factors, which they may be inherently bestowed with, or may acquire from the natural vector biting the host at the infection prelude, or may take over from the infecting host, to outmaneuver, evade, overcome, and/or suppress the host immunity, both innately and adaptively. This narrative review summarizes the up-to-date strategies exploited by a number of representative human parasites (protozoa and helminths) to counteract the target host immune defense. The revisited information should be useful for designing diagnostics and therapeutics as well as vaccines against the respective parasitic infections.

Myeloid Cell Mediated Immune Suppression in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA), the most common pancreatic cancer, is a nearly universally lethal malignancy. PDA is characterized by extensive infiltration of immunosuppressive myeloid cells, including tumor-associated macrophages and myeloid-derived suppressor cells. Myeloid cells in the tumor microenvironment inhibit cytotoxic T-cell responses promoting carcinogenesis. Immune checkpoint therapy has not been effective in PDA, most likely because of this robust immune suppression, making it critical to elucidate mechanisms behind this phenomenon. Here, we review myeloid cell infiltration and cellular crosstalk in PDA progression and highlight current therapeutic approaches to target myeloid cell-driven immune suppression.

Sex Matters: Physiological Abundance of Immuno-Regulatory CD71+ Erythroid Cells Impair Immunity in Females

Mature erythrocytes are the major metabolic regulators by transporting oxygen throughout the body. However, their precursors and progenitors defined as CD71+ Erythroid Cells (CECs) exhibit a wide range of immunomodulatory properties. Here, we uncover pronounced sexual dimorphism in CECs. We found female but not male mice, both BALB/c and C57BL/6, and human females were enriched with CECs. CECs, mainly their progenitors defined as CD45+CECs expressed higher levels of reactive oxygen species (ROS), PDL-1, VISTA, Arginase II and Arginase I compared to their CD45- counterparts. Consequently, CECs by the depletion of L-arginine suppress T cell activation and proliferation. Expansion of CECs in anemic mice and also post-menstrual cycle in women can result in L-arginine depletion in different microenvironments in vivo (e.g. spleen) resulting in T cell suppression. As proof of concept, we found that anemic female mice and mice adoptively transferred with CECs from anemic mice became more susceptible to Bordetella pertussis infection. These observations highlight the role of sex and anemia-mediated immune suppression in females. Notably, enriched CD45+CECs may explain their higher immunosuppressive properties in female BALB/c mice. Finally, we observed significantly more splenic central macrophages in female mice, which can explain greater extramedullary erythropoiesis and subsequently abundance of CECs in the periphery. Thus, sex-specific differences frequency in the frequency of CECs might be imprinted by differential erythropoiesis niches and hormone-dependent manner.

Age-related expansion and increased osteoclastogenic potential of myeloid-derived suppressor cells

Aging is associated with excessive bone loss that is not counteracted with the development of new bone. However, the mechanisms underlying age-related bone loss are not completely clear. Myeloid-derived suppressor cells (MDSCs) are a population of heterogenous immature myeloid cells with immunosuppressive functions that are known to stimulate tumor-induced bone lysis. In this study, we investigated the association of MDSCs and age-related bone loss in mice. Our results shown that aging increased the accumulation of MDSCs in the bone marrow and spleen, while in the meantime potentiated the osteoclastogenic activity of the CD11b⁺Ly6C^hiLy6G⁺ monocytic subpopulation of MDSCs. In addition, CD11b⁺Ly6C^hiLy6G⁺ MDSCs from old mice exhibited increased expression of c-fms compared to young mice, and were more sensitive to RANKL-induced osteoclast gene expression. On the other hand, old mice showed elevated production of IL-6 and receptor activator of nuclear factor kappa-B ligand (RANKL) in the circulation. Furthermore, IL-6 and RANKL were able to induce the proliferation of CD11b⁺Ly6C^hiLy6G⁺ MDSCs and up-regulate c-fms expression. Moreover, CD11b⁺Ly6C^hiLy6G⁺ MDSCs obtained from old mice showed increased antigen-specific T cell suppressive function, pStat3 expression, and cytokine production in response to inflammatory stimulation, compared to those cells obtained from young mice. Our findings suggest that CD11b⁺Ly6C^hiLy6G⁺ MDSCs are a source of osteoclast precursors that together with the presence of persistent, low-grade inflammation, contribute to age-associated bone loss in mice.

Arginine Signaling and Cancer Metabolism

Arginine is an amino acid critically involved in multiple cellular processes including the syntheses of nitric oxide and polyamines, and is a direct activator of mTOR, a nutrient-sensing kinase strongly implicated in carcinogenesis. Yet, it is also considered as a non- or semi-essential amino acid, due to normal cells' intrinsic ability to synthesize arginine from citrulline and aspartate via ASS1 (argininosuccinate synthase 1) and ASL (argininosuccinate lyase). As such, arginine can be used as a dietary supplement and its depletion as a therapeutic strategy. Strikingly, in over 70% of tumors, ASS1 transcription is suppressed, rendering the cells addicted to external arginine, forming the basis of arginine-deprivation therapy. In this review, we will discuss arginine as a signaling metabolite, arginine's role in cancer metabolism, arginine as an epigenetic regulator, arginine as an immunomodulator, and arginine as a therapeutic target. We will also provide a comprehensive summary of ADI (arginine deiminase)-based arginine-deprivation preclinical studies and an update of clinical trials for ADI and arginase. The different cell killing mechanisms associated with various cancer types will also be described.

Immune checkpoint blockade in triple negative breast cancer influenced by B cells through myeloid-derived suppressor cells

Triple negative breast cancer holds a dismal clinical outcome and as such, patients routinely undergo aggressive, highly toxic treatment regimens. Clinical trials for TNBC employing immune checkpoint blockade in combination with chemotherapy show modest prognostic benefit, but the percentage of patients that respond to treatment is low, and patients often succumb to relapsed disease. Here, we show that a combination immunotherapy platform utilizing low dose chemotherapy (FEC) combined with oncolytic virotherapy (oHSV-1) increases tumor-infiltrating lymphocytes, in otherwise immune-bare tumors, allowing 60% of mice to achieve durable tumor regression when treated with immune checkpoint blockade. Whole-tumor RNA sequencing of mice treated with FEC + oHSV-1 shows an upregulation of B cell receptor signaling pathways and depletion of B cells prior to the start of treatment in mice results in complete loss of therapeutic efficacy and expansion of myeloid-derived suppressor cells. Additionally, RNA sequencing data shows that FEC + oHSV-1 suppresses genes associated with myeloid-derived suppressor cells, a key population of cells that drive immune escape and mediate therapeutic resistance. These findings highlight the importance of tumor-infiltrating B cells as drivers of antitumor immunity and their potential role in the regulation of myeloid-derived suppressor cells.

Therapeutic Potential of Targeting Stromal Crosstalk-Mediated Immune Suppression in Pancreatic Cancer

The stroma-rich, immunosuppressive microenvironment is a hallmark of pancreatic ductal adenocarcinoma (PDA). Tumor cells and other cellular components of the tumor microenvironment, such as cancer associated fibroblasts, CD4+ T cells and myeloid cells, are linked by a web of interactions. Their crosstalk not only results in immune evasion of PDA, but also contributes to pancreatic cancer cell plasticity, invasiveness, metastasis, chemo-resistance, immunotherapy-resistance and radiotherapy-resistance. In this review, we characterize several prevalent populations of stromal cells in the PDA microenvironment and describe how the crosstalk among them drives and maintains immune suppression. We also summarize therapeutic approaches to target the stroma. With a better understanding of the complex cellular and molecular networks in PDA, strategies aimed at sensitizing PDA to chemotherapy or immunotherapy through re-programing the tumor microenvironment can be designed, and in turn lead to improved clinical treatment for pancreatic cancer patients.

Metabolomics in Bone Research

Identifying the changes in endogenous metabolites in response to intrinsic and extrinsic factors has excellent potential to obtain an understanding of cells, biofluids, tissues, or organisms' functions and interactions with the environment. The advantages provided by the metabolomics strategy have promoted studies in bone research fields, including an understanding of bone cell behaviors, diagnosis and prognosis of diseases, and the development of treatment methods such as implanted biomaterials. This review article summarizes the metabolism changes during osteogenesis, osteoclastogenesis, and immunoregulation in hard tissue. The second section of this review is dedicated to describing and discussing metabolite changes in the most relevant bone diseases: osteoporosis, bone injuries, rheumatoid arthritis, and osteosarcoma. We consolidated the most recent finding of the metabolites and metabolite pathways affected by various bone disorders. This collection can serve as a basis for future metabolomics-driven bone research studies to select the most relevant metabolites and metabolic pathways. Additionally, we summarize recent metabolic studies on metabolomics for the development of bone disease treatment including biomaterials for bone engineering. With this article, we aim to provide a comprehensive summary of metabolomics in bone research, which can be helpful for interdisciplinary researchers, including material engineers, biologists, and clinicians.

Multifunctional Nanodrug Mediates Synergistic Photodynamic Therapy and MDSCs-Targeting Immunotherapy of Colon Cancer

An ideal tumor treatment is supposed to eliminate the primary tumor and simultaneously trigger the host antitumor immune responses to prevent tumor recurrence and metastasis. Herein, a liposome encapsulating phosphoinositide 3-kinase gamma (PI3Kγ) inhibitor IPI-549 and photosensitizer chlorin e6 (Ce6), denoted by LIC, is prepared for colon cancer treatment. LIC internalized into CT26 cells generates reactive oxygen species (ROS) under laser irradiation to cause immunogenic tumor cell death, during which immunostimulatory signals such as calreticulin are released to further induce T lymphocyte-mediated tumor cell killing. Meanwhile, IPI-549 transported by liposome can inhibit PI3Kγ in the myeloid-derived suppressive cells (MDSCs), resulting in downregulation of arginase 1 (Arg-1) and ROS to promote MDSCs apoptosis and reduce their immunosuppressive activity to CD8⁺ T cells. LIC-mediated immunogenic photodynamic therapy synergizes with MDSCs-targeting immunotherapy, which significantly inhibits tumor growth via facilitating the dendritic cell maturation and tumor infiltration of CD8⁺ T cells while decreasing the tumor infiltration of immunosuppressive regulatory T cells, MDSCs, and M2-like tumor-associated macrophages. Moreover, the synergistic therapy increases the number of effector memory T cells (T_EM ) in spleen, which suggests a favorable immune memory to prevent tumor recurrence and metastasis. The Ce6 and IPI-549-coloaded multifunctional nanodrug demonstrates high efficacy in colon cancer treatment.

Doxorubicin, L-arginine, or their combination as a prophylactic agent against hepatic carcinoma in mice

Hepatocellular carcinoma (HCC) is one of the ten most commonly diagnosed cancers. Doxorubicin is an antibiotic used in cancer treatment protocols that has several side effects. L-Arginine is a non-essential amino acid that is used as immune system activation and antitumor drugs. Therefore, the current study was designed to compare using doxorubicin, L-arginine, or their combination as a prophylactic agent against hepatic carcinoma induced by hepatocellular carcinoma cells (HepG2) injection in mice. The mice were divided into five groups: normal mice and mice that received HepG2, doxorubicin and HepG2, L-arginine and HepG2, and doxorubicin, L-Arginine, and HepG2, respectively. Liver function test as, aspartate transaminase (AST) and alanine transaminase (ALT), and alpha-fetoprotein (AFP), caspase 3, interleukin 6 (IL-6), tumor necrotic factor (TNF), lipid peroxidation (NDA), and some antioxidant parameters were determined. A significant increase in AST and ALT, α-fetoprotein, TNF-α, and cytokines IL6 and MDA and a significant decrease in the serum caspase and liver catalase were determined in HepG2-injected mice. Moreover, some large hyperchromatic heptocytes were observed and the percentage of the positive area/field of HepPar-1, the most specific HCC marker, was 9.56%. Interestingly, mice that received doxorubicin, L-arginine, or their combination showed an improvement in some of the previous parameters. The improvement was more prominent with L-arginine administration.

Arginine-dependent immune responses

A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.

The Role of Amino Acids in the Crosstalk Between Mesenchymal Stromal Cells and Neoplastic Cells in the Hematopoietic Niche

Within the bone marrow hematopoietic cells are in close connection with mesenchymal stromal cells (MSCs), which influence the behavior and differentiation of normal or malignant lymphoid and myeloid cells. Altered cell metabolism is a hallmark of cancer, and changes in nutrient pools and fluxes are important components of the bidirectional communication between MSCs and hematological cancer cells. Among nutrients, amino acids play a significant role in cancer progression and chemo-resistance. Moreover, selected types of cancer cells are extremely greedy for glutamine, and significantly deplete the extracellular pool of the amino acid. As a consequence, this influences the behavior of MSCs in terms of either cytokine/chemokine secretion or differentiation potential. Additionally, a direct nutritional interaction exists between MSCs and immune cells. In particular, selected subpopulations of lymphocytes are dependent upon selected amino acids, such as arginine and tryptophan, for full differentiation and competence. This review describes and discusses the nutritional interactions existing in the neoplastic bone marrow niche between MSCs and other cell types, with a particular emphasis on cancer cells and immune cells. These relationships are discussed in the perspective of potential novel therapeutic strategies based on the interference on amino acid metabolism or intercellular fluxes.

Metabolism and function of polyamines in cancer progression

Polyamines are essential for the proliferation, differentiation, and development of eukaryotes. They include spermine, spermidine, and the diamine precursor putrescine, and are low-molecular-weight, organic polycations with more than two amino groups. Their intracellular concentrations are strictly maintained within a specific physiological range through several regulatory mechanisms in normal cells. In contrast, polyamine metabolism is dysregulated in many neoplastic states, including cancer. In various types of cancer, polyamine levels are elevated, and crosstalk occurs between polyamine metabolism and oncogenic pathways, such as mTOR and RAS pathways. Thus, polyamines might have potential as therapeutic targets in the prevention and treatment of cancer. The molecular mechanisms linking polyamine metabolism to carcinogenesis must be unraveled to develop novel inhibitors of polyamine metabolism. This overview describes the nature of polyamines, their association with carcinogenesis, the development of polyamine inhibitors and their potential, and the findings of clinical trials.

Serum Amyloid A Proteins and Their Impact on Metastasis and Immune Biology in Cancer

Simple Summary

The liver responds to systemic inflammation and injury in a coordinated manner, called the acute phase response. While this normal physiological response aims to restore homeostasis, malignant transformation coopts this biology to increase the risk for metastasis, immune evasion, and therapeutic resistance. In this Review, we discuss the importance of acute phase response proteins in regulating cancer biology and treatment efficacy. We also consider potential strategies to intervene on acute phase biology as an approach to improve outcomes in cancer.

Abstract

Cancer triggers the systemic release of inflammatory molecules that support cancer cell metastasis and immune evasion. Notably, this biology shows striking similarity to an acute phase response that is coordinated by the liver. Consistent with this, a role for the liver in defining cancer biology is becoming increasingly appreciated. Understanding the mechanisms that link acute phase biology to metastasis and immune evasion in cancer may reveal vulnerable pathways and novel therapeutic targets. Herein, we discuss a link between acute phase biology and cancer with a focus on serum amyloid A proteins and their involvement in regulating the metastatic cascade and cancer immunobiology.

Hampering Stromal Cells in the Tumor Microenvironment as a Therapeutic Strategy to Destem Cancer Stem Cells

Cancer stem cells (CSCs) within the tumor bulk play crucial roles in tumor initiation, recurrence and therapeutic resistance. In addition to intrinsic regulation, a growing body of evidence suggests that the phenotypes of CSCs are also regulated extrinsically by stromal cells in the tumor microenvironment (TME). Here, we discuss the current knowledge of the interplay between stromal cells and cancer cells with a special focus on how stromal cells drive the stemness of cancer cells and immune evasive mechanisms of CSCs. Knowledge gained from the interaction between CSCs and stromal cells will provide a mechanistic basis for the development of novel therapeutic strategies for the treatment of cancers.

Amino acid metabolism and signalling pathways: potential targets in the control of infection and immunity

Defences to pathogens such as SarCoV2 in mammals involves interactions between immune functions and metabolic pathways to eradicate infection while preventing hyperinflammation. Amino acid metabolic pathways represent with other antimicrobial agent potential targets for therapeutic strategies. iNOS-mediated production of NO from Arg is involved in the innate inflammatory response to pathogens and NO overproduction can induce hyperinflammation. The two Arg- and Trp-catabolising enzymes Arg1 and IDO1 reduce the hyperinflammation by an immunosuppressive effect via either Arg starvation (for Arg1) or via the immunoregulatory activity of the Trp-derived metabolites Kyn (for IDO1). In response to amino acid abundance mTOR activates the host protein translation and Coronaviruses use this machinery for their own protein synthesis and replication. In contrast GCN2, the sensor of amino acid starvation, activates pathways that restrict inflammation and viral replication. Gln depletion alters the immune response that become more suppressive, by favouring a regulatory T phenotype rather than a Th1 phenotype. Proliferating activated immune cells are highly dependent on Ser, activation and differentiation of T cells need enough Ser and dietary Ser restriction can inhibit their proliferation. Cys is strictly required for T-cell proliferation because they cannot convert Met to Cys. Restricting Met inhibits both viral RNA cap methylation and replication, and the proliferation of infected cells with an increased requirement for Met. Phe catabolism produces antimicrobial metabolites resulting in the inhibition of microbial growth and an immunosuppressive activity towards T lymphocytes.

Amino acid metabolism and signalling pathways: potential targets in the control of infection and immunity

Defences to pathogens such as SarCoV2 in mammals involves interactions between immune functions and metabolic pathways to eradicate infection while preventing hyperinflammation. Amino acid metabolic pathways represent with other antimicrobial agent potential targets for therapeutic strategies. iNOS-mediated production of NO from Arg is involved in the innate inflammatory response to pathogens and NO overproduction can induce hyperinflammation. The two Arg-catabolising enzymes Arg1 and IDO1 reduce the hyperinflammation by an immunosuppressive effect via either Arg starvation (for Arg1) or via the immunoregulatory activity of the Arg-derived metabolites Kyn (for IDO1). In response to amino acid abundance mTOR activates the host protein translation and Coronaviruses use this machinery for their own protein synthesis and replication. In contrast GCN2, the sensor of amino acid starvation, activates pathways that restrict inflammation and viral replication. Gln depletion alters the immune response that become more suppressive, by favouring a regulatory T phenotype rather than a Th1 phenotype. Proliferating activated immune cells are highly dependent on Ser, activation and differentiation of T cells need enough Ser and dietary Ser restriction can inhibit their proliferation. Cys is strictly required for T-cell proliferation because they cannot convert Met to Cys. Restricting Met inhibits both viral RNA cap methylation and replication, and the proliferation of infected cells with an increased requirement for Met. Phe catabolism produces antimicrobial metabolites resulting in the inhibition of microbial growth and an immunosuppressive activity towards T lymphocytes.

Tumor-Associated Macrophages as Multifaceted Regulators of Breast Tumor Growth

Breast cancer is the most commonly occurring cancer in women of Western countries and is the leading cause of cancer-related mortality. The breast tumor microenvironment contains immune cells, fibroblasts, adipocytes, mesenchymal stem cells, and extracellular matrix. Among these cells, macrophages or tumor-associated macrophages (TAMs) are the major components of the breast cancer microenvironment. TAMs facilitate metastasis of the breast tumor and are responsible for poor clinical outcomes. High TAM density was also found liable for the poor prognosis of breast cancer. These observations make altering TAM function a potential therapeutic target to treat breast cancer. The present review summarizes the origin of TAMs, mechanisms of macrophage recruitment and polarization in the tumor, and the contributions of TAMs in tumor progression. We have also discussed our current knowledge about TAM-targeted therapies and the roles of miRNAs and exosomes in re-educating TAM function.

Metabolic regulation in the immune response to cancer

Metabolic reprogramming in tumor‐immune interactions is emerging as a key factor affecting pro‐inflammatory carcinogenic effects and anticancer immune responses. Therefore, dysregulated metabolites and their regulators affect both cancer progression and therapeutic response. Here, we describe the molecular mechanisms through which microenvironmental, systemic, and microbial metabolites potentially influence the host immune response to mediate malignant progression and therapeutic intervention. We summarized the primary interplaying factors that constitute metabolism, immunological reactions, and cancer with a focus on mechanistic aspects. Finally, we discussed the possibility of metabolic interventions at multiple levels to enhance the efficacy of immunotherapeutic and conventional approaches for future anticancer treatments.

Aspects of the Tumor Microenvironment Involved in Immune Resistance and Drug Resistance

The tumor microenvironment (TME) is a complex and ever-changing "rogue organ" composed of its own blood supply, lymphatic and nervous systems, stroma, immune cells and extracellular matrix (ECM). These complex components, utilizing both benign and malignant cells, nurture the harsh, immunosuppressive and nutrient-deficient environment necessary for tumor cell growth, proliferation and phenotypic flexibility and variation. An important aspect of the TME is cellular crosstalk and cell-to-ECM communication. This interaction induces the release of soluble factors responsible for immune evasion and ECM remodeling, which further contribute to therapy resistance. Other aspects are the presence of exosomes contributed by both malignant and benign cells, circulating deregulated microRNAs and TME-specific metabolic patterns which further potentiate the progression and/or resistance to therapy. In addition to biochemical signaling, specific TME characteristics such as the hypoxic environment, metabolic derangements, and abnormal mechanical forces have been implicated in the development of treatment resistance. In this review, we will provide an overview of tumor microenvironmental composition, structure, and features that influence immune suppression and contribute to treatment resistance.

Complex Roles of Neutrophils during Arboviral Infections

Arboviruses are known to cause large-scale epidemics in many parts of the world. These arthropod-borne viruses are a large group consisting of viruses from a wide range of families. The ability of their vector to enhance viral pathogenesis and transmission makes the development of treatments against these viruses challenging. Neutrophils are generally the first leukocytes to be recruited to a site of infection, playing a major role in regulating inflammation and, as a result, viral replication and dissemination. However, the underlying mechanisms through which neutrophils control the progression of inflammation and disease remain to be fully understood. In this review, we highlight the major findings from recent years regarding the role of neutrophils during arboviral infections. We discuss the complex nature of neutrophils in mediating not only protection, but also augmenting disease pathology. Better understanding of neutrophil pathways involved in effective protection against arboviral infections can help identify potential targets for therapeutics.

All-trans-retinoic acid restores CD4+ T cell response after sepsis by inhibiting the expansion and activation of myeloid-derived suppressor cells

BACKGROUND

Patients are susceptible to immunosuppression in late-stage of sepsis, in which myeloid-derived suppressor cells (MDSCs) is an important contributor. This study aims to investigate whether all-trans-retinoic acid (ATRA), which has been proved to inhibit MDSCs generation in cancer, will ameliorate sepsis-induced immuno-suppression through modulating MDSCs.

METHODS

A clinically relevant "two-hit'' model of sepsis, the cecal ligation and puncture (CLP) model and secondary pneumonia model, were established in mice. The effects of ATRA on the mortality, the bacterial burden, the expansion and activity of CLP-induced MDSCs, as well as the function of CD4+ T cells were evaluated.

RESULTS

In CLP model, ATRA was found to reduce frequency of MDSCs in spleen of mice and inhibit activity of MDSCs by regulating the generation and activity of arginase-1 and iNOS, and the secretion of immune-supressive cytokines. ATRA administration eventually reduced mortality of secondary infection by Legionella pneumophila in CLP-surviving mice, which might be associated with the restoration of CD4+ T cells proliferating and secreting activity.

CONCLUSION

ATRA can restore CD4+ T cells dysfunction in sepsis by modulating the expansion and function of MDSCs and therefore provides a potential therapy that targets the immunosuppressive state of sepsis.

Immune Responses against Disseminated Tumor Cells

Most cancer-related deaths are a consequence of metastases, a series of linear events, notably the invasion-metastasis cascade. The current understanding of cancer immune surveillance derives from studies in primary tumors, but disseminated cancer cells acquire mutations and, in some cases, appear to progress independently after spreading from primary sites. An early step in this process is micrometastatic dissemination. As such, the equilibrium between the immune system and disseminated cancer cells controls the fate of the cancer. Immune checkpoint inhibitors (ICIs) exhibit significant clinical activity in patients, but the efficacy of ICIs depends on both the tumor and its microenvironment. Data often suggest that disseminated cancer cells are not adequately targeted by the immune system. In this review, we summarize the main basic findings of immune responses against disseminated tumor cells and their organ-specific characteristics. Such studies may provide new directions for cancer immune therapy.

Increased Arginase1 expression in tumor microenvironment promotes mammary carcinogenesis via multiple mechanisms

Arginine metabolism plays a significant role in regulating cell function, affecting tumor growth and metastatization. To study the effect of the arginine-catabolizing enzyme Arginase1 (ARG1) on tumor microenvironment, we generated a mouse model of mammary carcinogenesis by crossbreeding a transgenic mouse line overexpressing ARG1 in macrophages (FVBArg+/+) with the MMTV-Neu mouse line (FVBNeu+/+). This double transgenic line (FVBArg+/-;Neu+/+) showed a significant shortening in mammary tumor latency, and an increase in the number of mammary nodules. Transfer of tumor cells from FVBNeu+/+ into either FVB wild type or FVBArg+/+ mice resulted in increase regulatory T cells in the tumor infiltrate, suggestive of an impaired antitumor immune response. However, we also found increased frequency of tumor stem cells in tumors from FVBArg+/-;Neu+/+ transgenic compared with FVBNeu+/+ mice, suggesting that increased arginine metabolism in mammary tumor microenvironment may supports the cancer stem cells niche. We provide in vivo evidence of a novel, yet unexploited, mechanism through which ARG1 may contribute to tumor development.

Chinese Herbal Prescription Fu-Zheng-Qu-Xie Prevents Recurrence and Metastasis of Postoperative Early-Stage Lung Adenocarcinoma: A Prospective Cohort Study Followed with Potential Mechanism Exploration

Chinese herbal Fu-Zheng-Qu-Xie (FZQX) prescription has been found to improve the immune function and survival of patients with early-stage lung cancer. However, the therapeutic efficacy needs to be evaluated objectively, and the precise mechanism remains unclear. In the present study, a double-center, prospective cohort study was carried out to assess the clinical efficacy of the FZQX prescription in preventing the recurrence and metastasis of postoperative early-stage lung adenocarcinoma. Our results indicated that the FZQX prescription could significantly reduce the 3-year postoperative recurrence rate and improve the life quality. Moreover, the peripheral blood indices showed that the positive immune index (CD4 +T/CD8 +T) increased and the negative immune indices (CD8 +T, Myeloid-derived suppressor cells (MDSCs), Treg) decreased after treatment with the FZQX prescription. Since the positive regulatory effect of the FZQX prescription on immune function, a series of experiments were conducted to verify the tumor-suppressive effect and elucidate the underlying mechanisms. Through the MDSC clearance xenograft model, we confirmed that the FZQX prescription could effectively suppress tumor growth with lesser side effects in vivo, and MDSCs may be involved in the biological process of the FZQX prescription's intervention in lung cancer progression. By establishing the coculture system of MDSCs/LLC to simulate the immune microenvironment of lung cancer, the tumor suppression effect of the FZQX prescription was further validated by in vitro experiments. Besides, it was confirmed that the FZQX prescription could regulate MDSCs to remodel the immunosuppressive tumor microenvironment, thus exerting its preventive effect on relapse of lung cancer. Finally, the pathway activator and inhibitor were further used to explore the potential molecular mechanism. Results demonstrated that the IL-1β/NF-κB signaling pathway was one of the critical signaling pathways of FZQX prescription regulating MDSCs to prevent the recurrence and metastasis of lung adenocarcinoma.

Transforming growth factor-beta and liver injury in an arginine vasopressin-induced pregnant rat model

Objective

Approximately 30% of preeclamptic pregnancies exhibit abnormal liver function tests. We assessed liver injury-associated enzyme levels and circulating transforming growth factor beta (TGF-β) levels in an arginine vasopressin (AVP)-induced pregnant Sprague-Dawley rat model.

Methods

Pregnant and non-pregnant Sprague-Dawley rats (n=24) received AVP (150 ng/hr) subcutaneously via mini-osmotic pumps for 18 days. Blood pressure was measured, urine samples were collected, and all animals were euthanized via isoflurane. Blood was collected to measure circulating levels of TGF-β1-3 isomers and liver injury enzymes in pregnant AVP (PAVP), pregnant saline (PS), non-pregnant AVP (NAVP), and non-pregnant saline (NS) rats.

Results

The PAVP group showed significantly higher systolic and diastolic blood pressure than both saline-treated groups. The weight per pup was significantly lower in the AVP-treated group than in the saline group (p<0.05). Circulating TGF-β1-3 isomer levels were significantly higher in the PAVP rats than in the NS rats. However, similar TGF-β1 and TGF-β3 levels were noted in the PS and PAVP rats, while TGF-β2 levels were significantly higher in the PAVP rats. Circulating liver-type arginase-1 and 5'-nucleotidase levels were higher in the PAVP rats than in the saline group.

Conclusion

This is the first study to demonstrate higher levels of TGF-β2, arginase, and 5'-nucleotidase activity in PAVP than in PS rats. AVP may cause vasoconstriction and increase peripheral resistance and blood pressure, thereby elevating TGF-β and inducing the preeclampsia-associated inflammatory response. Future studies should explore the mechanisms through which AVP dysregulates liver injury enzymes and TGF-β in pregnant rats.

Chromatin accessibility governs the differential response of cancer and T cells to arginine starvation

Depleting the microenvironment of important nutrients such as arginine is a key strategy for immune evasion by cancer cells. Many tumors overexpress arginase, but it is unclear how these cancers, but not T cells, tolerate arginine depletion. In this study, we show that tumor cells synthesize arginine from citrulline by upregulating argininosuccinate synthetase 1 (ASS1). Under arginine starvation, ASS1 transcription is induced by ATF4 and CEBPβ binding to an enhancer within ASS1. T cells cannot induce ASS1, despite the presence of active ATF4 and CEBPβ, as the gene is repressed. Arginine starvation drives global chromatin compaction and repressive histone methylation, which disrupts ATF4/CEBPβ binding and target gene transcription. We find that T cell activation is impaired in arginine-depleted conditions, with significant metabolic perturbation linked to incomplete chromatin remodeling and misregulation of key genes. Our results highlight a T cell behavior mediated by nutritional stress, exploited by cancer cells to enable pathological immune evasion.

Immunosuppressive Effects of Myeloid-Derived Suppressor Cells in Cancer and Immunotherapy

The primary function of myeloid cells is to protect the host from infections. However, during cancer progression or states of chronic inflammation, these cells develop into myeloid-derived suppressor cells (MDSCs) that play a prominent role in suppressing anti-tumor immunity. Overcoming the suppressive effects of MDSCs is a major hurdle in cancer immunotherapy. Therefore, understanding the mechanisms by which MDSCs promote tumor growth is essential for improving current immunotherapies and developing new ones. This review explores mechanisms by which MDSCs suppress T-cell immunity and how this impacts the efficacy of commonly used immunotherapies.

CD4+ T-cell differentiation and function: Unifying glycolysis, fatty acid oxidation, polyamines NAD mitochondria

The progression through different steps of T-cell development, activation, and effector function is tightly bound to specific cellular metabolic processes. Previous studies established that T-effector cells have a metabolic bias toward aerobic glycolysis, whereas naive and regulatory T cells mainly rely on oxidative phosphorylation. More recently, the field of immunometabolism has drifted away from the notion that mitochondrial metabolism holds little importance in T-cell activation and function. Of note, T cells possess metabolic promiscuity, which allows them to adapt their nutritional requirements according to the tissue environment. Altogether, the integration of these metabolic pathways culminates in the generation of not only energy but also intermediates, which can regulate epigenetic programs, leading to changes in T-cell fate. In this review, we discuss the recent literature on how glycolysis, amino acid catabolism, and fatty acid oxidation work together with the tricarboxylic acid cycle in the mitochondrion. We also emphasize the importance of the electron transport chain for T-cell immunity. We also discuss novel findings highlighting the role of key enzymes, accessory pathways, and posttranslational protein modifications that distinctively regulate T-cell function and might represent prominent candidates for therapeutic purposes.

Host immune response against leishmaniasis and parasite persistence strategies: A review and assessment of recent research

Leishmaniasis, a neglected parasitic disease caused by a unicellular protozoan of the genus Leishmania, is transmitted through the bite of a female sandfly. The disease remains a major public health problem and is linked to tropical and subtropical regions, with an endemic picture in several regions, including East Africa, the Mediterranean basin and South America. The different causative species display a diversity of clinical presentations; therefore, the immunological data on leishmaniasis are both scarce and controversial for the different forms and infecting species of the parasite. The present review highlights the main immune parameters associated with leishmaniasis that might contribute to a better understanding of the pathogenicity of the parasite and the clinical outcomes of the disease. Our aim was to provide a concise overview of the immunobiology of the disease and the factors that influence it, as this knowledge may be helpful in developing novel chemotherapeutic and vaccine strategies.

Potential biomarkers of immune protection in human leishmaniasis

Leishmaniasis is a vector-borne neglected tropical disease endemic in over 100 countries around the world. Available control measures are not always successful, therapeutic options are limited, and there is no vaccine available against human leishmaniasis, although several candidate antigens have been evaluated over the last decades. Plenty of studies have aimed to evaluate the immune response development and a diverse range of host immune factors have been described to be associated with protection or disease progression in leishmaniasis; however, to date, no comprehensive biomarker(s) have been identified as surrogate marker of protection or exacerbation, and lack of enough information remains a barrier for vaccine development. Most of the current understanding of the role of different markers of immune response in leishmaniasis has been collected from experimental animal models. Although the data generated from the animal models are crucial, it might not always be extrapolated to humans. Here, we briefly review the events during Leishmania invasion of host cells and the immune responses induced against Leishmania in animal models and humans and their potential role as a biomarker of protection against human leishmaniasis.

Tumor-related stress regulates functional plasticity of MDSCs

Myeloid-derived suppressor cells (MDSCs) impair protective anti-tumor immunity and remain major obstacles that stymie the effectiveness of promising cancer therapies. Diverse tumor-derived stressors galvanize the differentiation, intra-tumoral expansion, and immunomodulatory function of MDSCs. These tumor-associated 'axes of stress' underwrite the immunosuppressive programming of MDSCs in cancer and contribute to the phenotypic/functional heterogeneity that characterize tumor-MDSCs. This review discusses various tumor-associated axes of stress that direct MDSC development, accumulation, and immunosuppressive function, as well as current strategies aimed at overcoming the detrimental impact of MDSCs in cancer. To better understand the constellation of signals directing MDSC biology, we herein summarize the pivotal roles, signaling mediators, and effects of reactive oxygen/nitrogen species-related stress, chronic inflammatory stress, hypoxia-linked stress, endoplasmic reticulum stress, metabolic stress, and therapy-associated stress on MDSCs. Although therapeutic targeting of these processes remains mostly pre-clinical, intercepting signaling through the axes of stress could overcome MDSC-related immune suppression in tumor-bearing hosts.

HDAC11 regulates expression of C/EBPβ and immunosuppressive molecules in myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) constitute a heterogeneous population of immature myeloid cells derived from bone marrow and negatively regulate both innate and adaptive immunity in the tumor microenvironment. Previously we have demonstrated that MDSCs lacking histone deacetylase 11 (HDAC11) displayed an increased suppressive activity against CD8+ T-cells. However, the mechanisms of HDAC11 that contribute to the suppressive function of MDSCs remain unclear. Here, we show that arginase activity and NO production is significantly higher in HDAC11 knockout MDSCs when compared with wild-type (WT) controls. In the absence of HDAC11, elevated arginase level and enzymatic activity were observed preferentially in the tumor-infiltrated granulocytic MDSCs, whereas iNOS expression and NO production were increased in the tumor-infiltrated monocytic MDSCs. Of note and for the first time, we demonstrated an association between the elevated expression of immunosuppressive molecules with up-regulation of the transcription factor C/EBPβ in MDSCs lacking HDAC11. Interestingly, the highest expression of C/EBPβ was observed among CD11b+ Gr-1+ MDSCs isolated from tumor-bearing mice. The additional demonstration that HDAC11 is recruited to the promoter region of C/EBPβ in WT MDSCs suggests a novel molecular mechanism by which HDAC11 influence the expression of immunosuppressive molecules in MDSCs through regulation of C/EBPβ gene expression.

Type I collagen deletion in αSMA+ myofibroblasts augments immune suppression and accelerates progression of pancreatic cancer

Stromal desmoplastic reaction in pancreatic ductal adenocarcinoma (PDAC) involves significant accumulation of type I collagen (Col1). However, the precise molecular and mechanistic contribution of Col1 in PDAC progression remains unknown. Activated pancreatic stellate cells/αSMA+ myofibroblasts are major contributors of Col1 in the PDAC stroma. We use a dual-recombinase genetic mouse model of spontaneous PDAC to delete Col1 specifically in myofibroblasts. This results in significant reduction of total stromal Col1 content and accelerates the emergence of PanINs and PDAC, decreasing overall survival. Col1 deletion leads to Cxcl5 upregulation in cancer cells via SOX9. Increase in Cxcl5 is associated with recruitment of myeloid-derived suppressor cells and suppression of CD8+ T cells, which can be attenuated with combined targeting of CXCR2 and CCR2 to restrain accelerated PDAC progression in the setting of stromal Col1 deletion. Our results unravel the fundamental role of myofibroblast-derived Co1l in regulating tumor immunity and restraining PDAC progression.

L-Citrulline: A Non-Essential Amino Acid with Important Roles in Human Health

L-Arginine (Arg) has been widely used due to its functional properties as a substrate for nitric oxide (NO) generation. However, L-citrulline (CIT), whose main natural source is watermelon, is a non-essential amino acid but which has important health potential. This review provides a comprehensive approach to different studies of the endogenous synthesis of CIT, metabolism, pharmacokinetics, and pharmacodynamics as well as its ergogenic effect in exercise performance. The novel aspect of this paper focuses on the different effects of CIT, citrulline malate and CIT from natural sources such as watermelon on several topics, including cardiovascular diseases, diabetes, erectile dysfunction, cancer, and exercise performance. CIT from watermelon could be a natural food-sourced substitute for pharmacological products and therefore the consumption of this fruit is promoted.