Acidosis improves uptake of antigens and MHC class I-restricted presentation by dendritic cells

Personalizing electrolytes in the dialysis prescription: what, why and how?

Maintenance hemodialysis patients suffer from multiple comorbidities and treatment-related complications. A personalized approach to hemodialysis prescription could reduce some of these burdens by preventing complications such as excessive changes in blood pressure, arrhythmias, post-dialysis fatigue and decreased quality of life. A patient-centered approach to dialysate electrolyte concentrations represents one such opportunity. In addition to modifications in dialysate electrolyte concentrations, consideration of individual factors such as patients' serum concentrations, medication profiles, nutritional status and comorbidities is critical to tailoring hemodialysis prescriptions to optimize patient outcomes. The development of personalized dialysis treatment depends on the collection of comprehensive patient data, advances in technology, resource allocation and patient involvement in decision-making. This review discusses how the treatment of maintenance hemodialysis patients could benefit from individualized changes in certain dialysis fluid components.

Unveiling cytokine charge disparity as a potential mechanism for immune regulation

Cytokines are small signaling proteins that regulate the immune responses to infection and tissue damage. Surface charges of cytokines determine their in vivo fate in immune regulation, e.g., half-life and distribution. The overall negative charges in the extracellular microenvironment and the acidosis during inflammation and infection may differentially impact cytokines with different surface charges for fine-tuned immune regulation via controlling tissue residential properties. However, the trend and role of cytokine surface charges has yet to be elucidated in the literature. Interestingly, we have observed that most pro-inflammatory cytokines have a negative charge, while most anti-inflammatory cytokines and chemokines have a positive charge. In this review, we extensively examined the surface charges of all cytokines and chemokines, summarized the pharmacokinetics and tissue adhesion of major cytokines, and analyzed the link of surface charge with cytokine biodistribution, activation, and function in immune regulation. Additionally, we identified that the general trend of charge disparity between pro- and anti-inflammatory cytokines represents a unique opportunity to develop precise immune modulation approaches, which can be applied to many inflammation-associated diseases including solid tumors, chronic wounds, infection, and sepsis.

Metabolic reprogramming in the tumor microenvironment: unleashing T cell stemness for enhanced cancer immunotherapy

T cells play a pivotal role in the immune system by distinguishing between various harmful pathogens and cancerous cells within the human body and initiating an immune response. Within the tumor microenvironment (TME), immune effector T cells encounter both immunosuppressive cells and factors that hinder their functionality. Additionally, they endure robust and persistent antigenic stimulation, often leading to exhaustion and apoptosis. However, the stemness of T cells, characterized by their ability to survive and self-renew over extended periods, represents a primary target in immune checkpoint therapies such as anti-PD-1 therapy. T cell stemness encompasses specific memory T cell subsets and progenitor-exhausted T cells with stem cell-like properties. Therefore, understanding the impact of the TME on T cell stemness, including factors like K+, lactate, and H+, holds significant importance and can facilitate the mitigation of terminal T-cell depletion, the identification of potential resilient biomarkers or therapeutic targets resistant to immune checkpoint therapies, and ultimately lead to sustained anti-tumor effects. Thus, it offers a novel perspective for advancing tumor immunotherapy.

How protons pave the way to aggressive cancers

Cancers undergo sequential changes to proton (H+) concentration and sensing that are consequences of the disease and facilitate its further progression. The impact of protonation state on protein activity can arise from alterations to amino acids or their titration. Indeed, many cancer-initiating mutations influence pH balance, regulation or sensing in a manner that enables growth and invasion outside normal constraints as part of oncogenic transformation. These cancer-supporting effects become more prominent when tumours develop an acidic microenvironment owing to metabolic reprogramming and disordered perfusion. The ensuing intracellular and extracellular pH disturbances affect multiple aspects of tumour biology, ranging from proliferation to immune surveillance, and can even facilitate further mutagenesis. As a selection pressure, extracellular acidosis accelerates disease progression by favouring acid-resistant cancer cells, which are typically associated with aggressive phenotypes. Although acid-base disturbances in tumours often occur alongside hypoxia and lactate accumulation, there is now ample evidence for a distinct role of H+-operated responses in key events underpinning cancer. The breadth of these actions presents therapeutic opportunities to change the trajectory of disease.

pH sensing at the intersection of tissue homeostasis and inflammation

pH is tightly maintained at cellular, tissue, and systemic levels, and altered pH - particularly in the acidic range - is associated with infection, injury, solid tumors, and physiological and pathological inflammation. However, how pH is sensed and regulated and how it influences immune responses remain poorly understood at the tissue level. Applying conceptual frameworks of homeostatic and inflammatory circuitries, we categorize cellular and tissue components engaged in pH regulation, drawing parallels from established cases in physiology. By expressing various intracellular (pHi) and extracellular pH (pHe)-sensing receptors, the immune system may integrate information on tissue and cellular states into the regulation of homeostatic and inflammatory programs. We introduce the novel concept of resistance and adaptation responses to rationalize pH-dependent immunomodulation intertwined with homeostatic equilibrium and inflammatory control. We discuss emerging challenges and opportunities in understanding the immunological roles of pH sensing, which might reveal new strategies to combat inflammation and restore tissue homeostasis.

Impaired function of dendritic cells within the tumor microenvironment

Dendritic cells (DCs), a class of professional antigen-presenting cells, are considered key factors in the initiation and maintenance of anti-tumor immunity due to their powerful ability to present antigen and stimulate T-cell responses. The important role of DCs in controlling tumor growth and mediating potent anti-tumor immunity has been demonstrated in various cancer models. Accordingly, the infiltration of stimulatory DCs positively correlates with the prognosis and response to immunotherapy in a variety of solid tumors. However, accumulating evidence indicates that DCs exhibit a significantly dysfunctional state, ultimately leading to an impaired anti-tumor immune response due to the effects of the immunosuppressive tumor microenvironment (TME). Currently, numerous preclinical and clinical studies are exploring immunotherapeutic strategies to better control tumors by restoring or enhancing the activity of DCs in tumors, such as the popular DC-based vaccines. In this review, an overview of the role of DCs in controlling tumor progression is provided, followed by a summary of the current advances in understanding the mechanisms by which the TME affects the normal function of DCs, and concluding with a brief discussion of current strategies for DC-based tumor immunotherapy.

Acidosis significantly alters immune checkpoint expression profiles of T cells from oesophageal adenocarcinoma patients

Tumour acidosis contributes to cancer progression by inhibiting anti-tumour immunity. However, the effect of acidosis on anti-tumour T cell phenotypes in oesophageal adenocarcinoma (OAC) is unknown. Therefore, this study investigated the effect of acidosis on anti-tumour T cell profiles and if immune checkpoint blockade (ICB) could enhance anti-tumour T cell immunity under acidosis. Acidic conditions substantially altered immune checkpoint expression profiles of OAC patient-derived T cells, upregulating TIM-3, LAG-3 and CTLA-4. Severe acidosis (pH 5.5) significantly decreased the percentage of central memory CD4⁺ T cells, an effect that was attenuated by ICB treatment. ICB increased T cell production of IFN-γ under moderate acidosis (pH 6.6) but not severe acidosis (pH 5.5) and decreased IL-10 production by T cells under severe acidic conditions only. A link between lactate and metastasis was also depicted; patients with nodal metastasis had higher serum lactate levels (p = 0.07) which also positively correlated with circulating levels of pro-angiogenic factor Tie-2. Our findings establish that acidosis-induced upregulation of immune checkpoints on T cells may potentially contribute to immune evasion and disease progression in OAC. However, acidic conditions curtailed ICB efficacy, supporting a rationale for utilizing systemic oral buffers to neutralize tumour acidity to improve ICB efficacy. Study schematic-PBMCs were isolated from OAC patients (A) and expanded ex vivo for 7 days using anti-CD3/28 +IL-2 T cell activation protocol (B) and further cultured for 48 h under increasing acidic conditions in the absence or presence of immune checkpoint blockade (nivolumab, ipilimumab or dual nivolumab + ipilimumab) (C). Immunophenotyping was then carried out to assess immune checkpoint expression profiles and anti-tumour T cell phenotypes (D). Serum lactate was assessed in OAC patients (E-F) and levels were correlated with patient demographics (G) and the levels of circulating immune/pro-angiogenic cytokines that were determined by multiplex ELISA (H). Key Findings-severe acidic conditions upregulated multiple immune checkpoints on T cells (I). Efficacy of ICB was curtailed under severe acidic conditions (J). Circulating lactate levels positively correlated with circulating levels of pro-angiogenic factor tie-2 and higher serum lactate levels were found in patients who had nodal metastasis (K).

Nucleic acid-triggered tumoral immunity propagates pH-selective therapeutic antibodies through tumor-driven epitope spreading

Important roles of humoral tumor immunity are often pointed out; however, precise profiles of dominant antigens and developmental mechanisms remain elusive. We systematically investigated the humoral antigens of dominant intratumor immunoglobulin clones found in human cancers. We found that approximately half of the corresponding antigens were restricted to strongly and densely negatively charged polymers, resulting in simultaneous reactivities of the antibodies to both densely sulfated glycosaminoglycans (dsGAGs) and nucleic acids (NAs). These anti-dsGAG/NA antibodies matured and expanded via intratumoral immunological driving force of innate immunity via NAs. These human cancer-derived antibodies exhibited acidic pH-selective affinity across both antigens and showed specific reactivity to diverse spectrums of human tumor cells. The antibody-drug conjugate exerted therapeutic effects against multiple cancers in vivo by targeting cell surface dsGAG antigens. This study reveals that intratumoral immunological reactions propagate tumor-oriented immunoglobulin clones and demonstrates a new therapeutic modality for the universal treatment of human malignancies.

Tumor acidity: From hallmark of cancer to target of treatment

Tumor acidity is one of the cancer hallmarks and is associated with metabolic reprogramming and the use of glycolysis, which results in a high intracellular lactic acid concentration. Cancer cells avoid acid stress major by the activation and expression of proton and lactate transporters and exchangers and have an inverted pH gradient (extracellular and intracellular pHs are acid and alkaline, respectively). The shift in the tumor acid–base balance promotes proliferation, apoptosis avoidance, invasiveness, metastatic potential, aggressiveness, immune evasion, and treatment resistance. For example, weak-base chemotherapeutic agents may have a substantially reduced cellular uptake capacity due to “ion trapping”. Lactic acid negatively affects the functions of activated effector T cells, stimulates regulatory T cells, and promotes them to express programmed cell death receptor 1. On the other hand, the inversion of pH gradient could be a cancer weakness that will allow the development of new promising therapies, such as tumor-targeted pH-sensitive antibodies and pH-responsible nanoparticle conjugates with anticancer drugs. The regulation of tumor pH levels by pharmacological inhibition of pH-responsible proteins (monocarboxylate transporters, H⁺-ATPase, etc.) and lactate dehydrogenase A is also a promising anticancer strategy. Another idea is the oral or parenteral use of buffer systems, such as sodium bicarbonate, to neutralize tumor acidity. Buffering therapy does not counteract standard treatment methods and can be used in combination to increase effectiveness. However, the mechanisms of the anticancer effect of buffering therapy are still unclear, and more research is needed. We have attempted to summarize the basic knowledge about tumor acidity.

Norcantharidin Induces Immunogenic Cell Death of Bladder Cancer Cells through Promoting Autophagy in Acidic Culture

The acidic tumor microenvironment stands as a major obstacle to the efficient elimination of tumor cells. Norcantharidin (NCTD) is a powerful antitumor agent with multiple bioactivities. However, the effect of NCTD under acidic conditions is still unclear. Here, we report that NCTD can efficiently kill bladder cancer (BC) cells in acidic culture, and more intriguingly, NCTD can induce immunogenic cell death (ICD), thereby promoting antitumor immunity. In NCTD-treated BC cells, the surface-exposed calreticulin (ecto-CALR) was significantly increased. Consistently, co-culture with these cells promoted dendritic cell (DC) maturation. The NCTD-induced ICD is autophagy dependent, as autophagy inhibition completely blocked the NCTD-induced ecto-CALR and DC maturation. In addition, the DC showed a distinct maturation phenotype (CD80^high CD86^low) in acidic culture, as compared to that in physiological pH (CD⁸⁰ high CD86^high). Finally, the NCTD-induced ICD was validated in a mouse model. NCTD treatment significantly increased the tumor-infiltrating T lymphocytes in MB49 bladder cancer mice. Immunizing mice with NCTD-treated MB49 cells significantly increased tumor-free survival as compared to control. These findings demonstrate that NCTD could induce ICD in an acidic environment and suggest the feasibility to combine NCTD with anticancer immunotherapy to treat BC.

Lipid-Laden Macrophages and Inflammation in Atherosclerosis and Cancer: An Integrative View

Atherosclerotic arterial plaques and malignant solid tumors contain macrophages, which participate in anaerobic metabolism, acidosis, and inflammatory processes inherent in the development of either disease. The tissue-resident macrophage populations originate from precursor cells derived from the yolk sac and from circulating bone marrow-derived monocytes. In the tissues, they differentiate into varying functional phenotypes in response to local microenvironmental stimulation. Broadly categorized, the macrophages are activated to polarize into proinflammatory M1 and anti-inflammatory M2 phenotypes; yet, noticeable plasticity allows them to dynamically shift between several distinct functional subtypes. In atherosclerosis, low-density lipoprotein (LDL)-derived cholesterol accumulates within macrophages as cytoplasmic lipid droplets thereby generating macrophage foam cells, which are involved in all steps of atherosclerosis. The conversion of macrophages into foam cells may suppress the expression of given proinflammatory genes and thereby initiate their transcriptional reprogramming toward an anti-inflammatory phenotype. In this particular sense, foam cell formation can be considered anti-atherogenic. The tumor-associated macrophages (TAMs) may become polarized into anti-tumoral M1 and pro-tumoral M2 phenotypes. Mechanistically, the TAMs can regulate the survival and proliferation of the surrounding cancer cells and participate in various aspects of tumor formation, progression, and metastasis. The TAMs may accumulate lipids, but their type and their specific roles in tumorigenesis are still poorly understood. Here, we discuss how the phenotypic and functional plasticity of macrophages allows their multifunctional response to the distinct microenvironments in developing atherosclerotic lesions and in developing malignant tumors. We also discuss how the inflammatory reactions of the macrophages may influence the development of atherosclerotic plaques and malignant tumors, and highlight the potential therapeutic effects of targeting lipid-laden macrophages in either disease.

Acid Microenvironment in Bone Sarcomas

Simple Summary

Although rare, malignant bone sarcomas have devastating clinical implications for the health and survival of young adults and children. To date, efforts to identify the molecular drivers and targets have focused on cancer cells or on the interplay between cancer cells and stromal cells in the tumour microenvironment. On the contrary, in the current literature, the role of the chemical-physical conditions of the tumour microenvironment that may be implicated in sarcoma aggressiveness and progression are poorly reported and discussed. Among these, extracellular acidosis is a well-recognized hallmark of bone sarcomas and promotes cancer growth and dissemination but data presented on this topic are fragmented. Hence, we intended to provide a general and comprehensive overview of the causes and implications of acidosis in bone sarcoma.

Abstract

In bone sarcomas, extracellular proton accumulation is an intrinsic driver of malignancy. Extracellular acidosis increases stemness, invasion, angiogenesis, metastasis, and resistance to therapy of cancer cells. It reprograms tumour-associated stroma into a protumour phenotype through the release of inflammatory cytokines. It affects bone homeostasis, as extracellular proton accumulation is perceived by acid-sensing ion channels located at the cell membrane of normal bone cells. In bone, acidosis results from the altered glycolytic metabolism of bone cancer cells and the resorption activity of tumour-induced osteoclasts that share the same ecosystem. Proton extrusion activity is mediated by extruders and transporters located at the cell membrane of normal and transformed cells, including vacuolar ATPase and carbonic anhydrase IX, or by the release of highly acidic lysosomes by exocytosis. To date, a number of investigations have focused on the effects of acidosis and its inhibition in bone sarcomas, including studies evaluating the use of photodynamic therapy. In this review, we will discuss the current status of all findings on extracellular acidosis in bone sarcomas, with a specific focus on the characteristics of the bone microenvironment and the acid-targeting therapeutic approaches that are currently being evaluated.

From Pinocytosis to Methuosis-Fluid Consumption as a Risk Factor for Cell Death

The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV is incorporated within an hour and membrane area equivalent to the cell's surface within 30 min. Since neither fluid uptake nor membrane consumption leads to swelling or shrinkage, cells must be equipped with potent volume regulatory mechanisms. Normally, cells respond to outwardly or inwardly directed osmotic gradients by a volume decrease and increase, respectively, i.e., they shrink or swell but then try to recover their CV. However, when a cell death (CD) pathway is triggered, CV persistently decreases in isotonic conditions in apoptosis and it increases in necrosis. One type of CD associated with cell swelling is due to a dysfunctional pinocytosis. Methuosis, a non-apoptotic CD phenotype, occurs when cells accumulate too much fluid by macropinocytosis. In contrast to functional pinocytosis, in methuosis, macropinosomes neither recycle nor fuse with lysosomes but with each other to form giant vacuoles, which finally cause rupture of the plasma membrane (PM). Understanding methuosis longs for the understanding of the ionic mechanisms of cell volume regulation (CVR) and vesicular volume regulation (VVR). In nascent macropinosomes, ion channels and transporters are derived from the PM. Along trafficking from the PM to the perinuclear area, the equipment of channels and transporters of the vesicle membrane changes by retrieval, addition, and recycling from and back to the PM, causing profound changes in vesicular ion concentrations, acidification, and-most importantly-shrinkage of the macropinosome, which is indispensable for its proper targeting and cargo processing. In this review, we discuss ion and water transport mechanisms with respect to CVR and VVR and with special emphasis on pinocytosis and methuosis. We describe various aspects of the complex mutual interplay between extracellular and intracellular ions and ion gradients, the PM and vesicular membrane, phosphoinositides, monomeric G proteins and their targets, as well as the submembranous cytoskeleton. Our aim is to highlight important cellular mechanisms, components, and processes that may lead to methuotic CD upon their derangement.

The antagonistic effect of magnesium hydroxide particles on vascular endothelial activation induced by acidic PLGA degradation products

Although drug-eluting stents (DESs) are mainly coated with biodegradable polymers such as PLGA and PLLA, their acidic degradation products can alter the local microenvironment and affect the homeostasis of adjacent tissue. Previously, we developed anti-inflammatory PLGA-based materials including magnesium hydroxide (MH) to relieve the side effects caused by PLGA degradation. However, the underlying molecular mechanism of its protective effects has not yet been clarified. Here, we demonstrated the pathological mechanism of vascular endothelial activation caused by PLGA by-products. The PLGA by-products accumulated in HCAECs through MCT1, followed by oxidative stress and the activation of the MAPK/NF-κB signaling pathway. Finally, the PLGA by-products increased the expression of VCAM-1 as well as the secretion of proinflammatory cytokines. However, the addition of MH particles significantly diminished the activation of this molecular pathway and the expression of inflammation-related factors induced by acidic PLGA degradation products. Furthermore, Mg2+ released from MH particles restored endothelial function in both intracellular and extracellular spaces. Taken together, MH particles prevent the accumulation of PLGA degradation products in HCAECs, thereby repressing the associated vascular endothelial activation. These findings on the biochemical mechanisms are expected to provide important clues for addressing the safety issues in nearly all biodegradable polymer-based implants.

Therapeutic vaccination against leukaemia via the sustained release of co-encapsulated anti-PD-1 and a leukaemia-associated antigen

Therapeutic leukaemia vaccines have shown modest potency. Here, we show that the co-encapsulation of a leukaemia-associated epitope peptide highly expressed in leukaemia patients and of the immune checkpoint inhibitor anti-programmed-cell-death-protein-1 (anti-PD-1) in degradable poly(lactic acid) microcapsules resulted in the sustained release of the peptide and of the antibody, which led to the recruitment of activated antigen-presenting cells to the injection site, their uptake of the peptide and the transportation of the anti-PD-1 antibody to lymph nodes, enhancing the expansion of epitope-specific T cells and the activation of cytotoxic T cells. After single subcutaneous injections of vaccine formulations with different epitope peptides, mice bearing leukaemia xenografts derived from humanized cell lines or from primary cells from patients showed better therapeutic outcomes than mice receiving repeated injections of free antigen, antibody and a commercial adjuvant. The sustained release of a tumour-associated peptide and of anti-PD-1 may represent a generalizable strategy for boosting antitumour immune responses to leukaemia.

Bicarbonate enhances the inflammatory response by activating JAK/STAT signalling in LPS + IFN-γ-stimulated macrophages

Macrophages, which develop by changing their functions according to various environmental conditions and stimuli, defend against the pathogens and play roles in homoeostasis and disease states. Bicarbonate (HCO3-) is important in the maintenance of intracellular and extracellular pH in the body. However, the effects of bicarbonate on macrophage function have not been examined. In this study, we investigated the effects of bicarbonate on macrophage activation in lipopolysaccharide (LPS) and interferon (IFN)-γ (LPS + IFN-γ)-stimulated murine macrophage-like RAW264.7 cells. The expression of the interleukin (IL)-6, inducible nitric oxide (NO) synthase and cyclooxygenase-2 genes was enhanced by sodium bicarbonate (NaHCO3) in a concentration-dependent manner in LPS + IFN-γ-stimulated RAW264.7 cells. The production of IL-6, NO2- and prostaglandin E2 was also increased by treatment with NaHCO3 in these cells. Moreover, NaHCO3-mediated elevation of inflammatory gene expression was abrogated by solute carrier (SLC) transporter inhibitors. Furthermore, its NaHCO3-mediated activation was negated by a JAK inhibitor , tofacitinib. NaHCO3-enhanced phosphorylation of STAT1, and its enhancement was abrogated by pre-treating with SLC transporter inhibitors in LPS + IFN-γ-stimulated RAW264.7 cells. In addition, similar results were obtained in murine bone marrow-derived macrophages. These results indicate that bicarbonate enhanced the inflammatory response through the JAK/STAT signalling in LPS + IFN-γ-stimulated macrophages.

The oncogenic and clinical implications of lactate induced immunosuppression in the tumour microenvironment

The tumour microenvironment is of critical importance in cancer development and progression and includes the surrounding stromal and immune cells, extracellular matrix, and the milieu of metabolites and signalling molecules in the intercellular space. To support sustained mitotic activity cancer cells must reconfigure their metabolic phenotype. Lactate is the major by-product of such metabolic alterations and consequently, accumulates in the tumour. Lactate actively contributes to immune evasion, a hallmark of cancer, by directly inhibiting immune cell cytotoxicity and proliferation. Furthermore, lactate can recruit and induce immunosuppressive cell types, such as regulatory T cells, tumour-associated macrophages, and myeloid-derived suppressor cells which further suppress anti-tumour immune responses. Given its roles in oncogenesis, measuring intratumoural and systemic lactate levels has shown promise as a both predictive and prognostic biomarker in several cancer types. The efficacies of many anti-cancer therapies are limited by an immunosuppressive TME in which lactate is a major contributor, therefore, targeting lactate metabolism is a priority. Developing inhibitors of key proteins in lactate metabolism such as GLUT1, hexokinase, LDH, MCT and HIF have shown promise in preclinical studies, however there is a corresponding lack of success in human trials so far. This may be explained by a weakness of preclinical models that fail to reproduce the complexities of metabolic interactions in natura. The future of these therapies may be as an adjunct to more conventional treatments.

Motility and Mechanical Properties of Dendritic Cells Deteriorated by Extracellular Acidosis

Dendritic cells (DCs) are the most powerful antigen-presenting cells known to date and play an important role in initiating and amplifying both innate and adaptive immune responses. Extracellular acidosis is an important hallmark of a variety of inflammatory processes and solid tumors. However, few studies have focused on the effect of extracellular acidosis on DCs and their functions. Cellular mechanical properties reflect the relationship between cell structure and function, including cytoskeleton (especially F-actin organization), membrane negative charges, membrane fluidity, and osmotic fragility. The study investigated the effects of extracellular acidosis on the DCs functions from the perspective of cellular migration and mechanical properties. The results showed that migration ability, F-actin contents, and membrane negative charges of DCs were reduced by extracellular acidosis no matter whether LPS stimulated its maturation or not. And these functions could not return to normal after removing acidic microenvironment, which revealed that the function impairment induced by extracellular acidosis might be irreversible. In addition, the proliferation capacity of stimulated allogeneic T cells was impaired by extracellular acidosis. Our results suggest extracellular acidosis may play an immunosuppressive role in DCs-mediated immune process.

Lactate Exposure Promotes Immunosuppressive Phenotypes in Innate Immune Cells

Introduction

Lactate secreted by tumors is not just a byproduct, but rather an active modulator of immune cells. There are few studies aimed at investigating the true effect of lactate, which is normally confounded by pH. Such a knowledge gap needs to be addressed. Herein, we studied the immunomodulatory effects of lactate on dendritic cells (DCs) and macrophages (MΦs).

Methods

Bone marrow-derived innate immune cells were treated with 50 mM sodium lactate (sLA) and incubated for 2 days or 5 days at 37 °C. Controls included media, lipopolysaccharide (LPS), MCT inhibitors (α-cyano-4-hydroxycinnamic acid and AR-C15585). Flow cytometric analysis of immune phenotypes were performed by incubating cells with specific marker antibodies and viability dye. Differential expression analyses were conducted on R using limma-voom and adjusted p-values were generated using the Bejamini-Hochberg Procedure.

Results

Lactate exposure attenuated DC maturation through the downregulation of CD80 and MHCII expression under LPS stimulation. For MΦs, lactate exposure resulted in M2 polarization as evidenced by the reduction of M1 markers (CD38 and iNOS), and the increase in expression of CD163 and Arg1. We also revealed the role of monocarboxylate transporters (MCTs) in mediating lactate effect in MΦs. MCT4 inhibition significantly boosted lactate M2 polarization, while blocking of MCT1/2 failed to reverse the immunosuppressive effect of lactate, correlating with the result of gene expression that lactate increased MCT4 expression, but downregulated the expression of MCT1/2.

Conclusions

This research provides valuable insight on the influence of metabolic products on tumor immunity and will help to identify novel metabolic targets for augmenting cancer immunotherapies.

Role of microenvironmental acidity and tumor exosomes in cancer immunomodulation

Tumor microenvironment (TME) is a complex milieu in which tumor grows, develops and progresses through a complex bi-directional cross-talk with immune-, stromal cells, and the extracellular matrix (ECM). In this context, tumor-derived exosomes (TE) drive the fate of tumor cells through a stimulatory or inhibitory role on immune system. In fact, TE can induce the apoptosis of cells of the immune surveillance, and enhance the proliferation and survival of stromal cells that sustain tumor development. However, depending on the molecular cargo, TE are also able to stimulate anti-tumor immune response. TME is mainly characterized by the acidic pH that contributes to tumor development, through multiple mechanisms. Among these, the impairment of tumor immune surveillance does occur within acidic TME, and is directly mediated by acidic pH or by molecular cargo carried by TE. Little is known about the role of TE in immunomodulation in acidic conditions. The present review summarizes the studies describing the role of microenvironmental acidity and TE in immune system modulation.

T-cells produce acidic niches in lymph nodes to suppress their own effector functions

The acidic pH of tumors profoundly inhibits effector functions of activated CD8 + T-cells. We hypothesize that this is a physiological process in immune regulation, and that it occurs within lymph nodes (LNs), which are likely acidic because of low convective flow and high glucose metabolism. Here we show by in vivo fluorescence and MR imaging, that LN paracortical zones are profoundly acidic. These acidic niches are absent in athymic Nu/Nu and lymphodepleted mice, implicating T-cells in the acidifying process. T-cell glycolysis is inhibited at the low pH observed in LNs. We show that this is due to acid inhibition of monocarboxylate transporters (MCTs), resulting in a negative feedback on glycolytic rate. Importantly, we demonstrate that this acid pH does not hinder initial activation of naïve T-cells by dendritic cells. Thus, we describe an acidic niche within the immune system, and demonstrate its physiological role in regulating T-cell activation.

Environmental and Endogenous Acids Can Trigger Allergic-Type Airway Reactions

Inflammatory allergic and nonallergic respiratory disorders are spreading worldwide and often coexist. The root cause is not clear. This review demonstrates that, from a biochemical point of view, it is ascribable to protons (H+) released into cells by exogenous and endogenous acids. The hypothesis of acids as the common cause stems from two considerations: (a) it has long been known that exogenous acids present in air pollutants can induce the irritation of epithelial surfaces, particularly the airways, inflammation, and bronchospasm; (b) according to recent articles, endogenous acids, generated in cells by phospholipases, play a key role in the biochemical mechanisms of initiation and progression of allergic-type reactions. Therefore, the intracellular acidification and consequent Ca2+ increase, induced by protons generated by either acid pollutants or endogenous phospholipases, may constitute the basic mechanism of the multimorbidity of these disorders, and environmental acidity may contribute to their spread.

Protonation-Activity Relationship of Bioinspired Ionizable Glycomimetics for the Growth Inhibition of Bacteria

Variations in physiological parameters (i.e., pH, redox potential, and ions) for distinct types of diseases make them attractive targets. Ionizable groups capable of pH-dependent charge conversion impart pH-switchable materials under acid condition through the protonation effect, which stimulates the emergence of various pH-inspired materials. However, it is confusing to distinguish preferable groups for high-efficiency drug-delivery vehicles attributing to the lack of perceiving the relationship between protonation and activity. Herein, we developed a series of bioinspired ionizable glycomimetics responses to the ambient variation from physiological environment (pH 7.4) to bacterial infectious acidic microenvironment (pH 6.0) to explore the protonation-activity relationship of various ionizable groups. The nanoparticles are coated with bacterial adhesion molecules galactose and fucose to target Pseudomonas aeruginosa. Moreover, the particle cores were composed of ionizable polymers responding to acidic microenvironment changes and entrapped antibiotic payload. Ionizable glyconanoparticles targeted bacteria and local cues as triggers to transfer payloads in on-demand patterns for the inhibition of bacteria-related infection. Significantly, we find that the nanoparticles with the pH-sensitive block of ionizable poly(2-(diisopropylamino)ethyl methacrylate) (pDPA) exhibit predominant bacterial adhesion and killing and growth inhibition of biofilm in acid environment (pH 6.0) due to the ionizable polymer protonation effect with more positive charge cooperated with the lectin-targeted effect of polysaccharide causing a huge bacterial aggregation and a highly favorable germicidal effect. The nanoparticles with poly(2-(hexamethyleneimino)ethyl methacrylate) (pHMEMA) have suboptimal antibacterial activity but advanced protonation at pH 6.3 compared to pDPA at 6.1, suggesting its selection as an applicable pH-switchable group for a slightly higher acid microenvironment like tumor (pH 6.9-6.5) because of the efficient performance after protonation than at deprotonation. On the other hand, the glycomimetic containing poly(2-(dibutylamino)ethyl methacrylate) (pDBA) as a pH-sensitive moiety displayed weak antimicrobial activity and superior stability before protonation (pH 4.7), which make it possible to prevent premature drug leakage, suggesting that pDBA is a good candidate to be applied to construct pH-sensitive drug-delivery carriers for the treatment of bacteria-related infection with a low acidic microenvironment. Overall, the structure-activity relationship of ionizable glycomimetics for the inhibition of bacteria signifies not only the development of a drug-delivery system but also the mechanism-dependent treatment of nanomedicine for infectious diseases.

Association Between Severity of Diabetic Ketoacidosis at Diagnosis and Multiple Autoimmunity in Children With Type 1 Diabetes Mellitus: A Study From a Greek Tertiary Centre

OBJECTIVES

Type 1 diabetes mellitus is a chronic disorder associated with development of autoimmunity. In this work, we studied the relationship between severity of acidosis at diagnosis and future risk for autoimmunity development in children with type 1 diabetes.

METHODS

We investigated the presence of associated autoimmunity in 144 children with type 1 diabetes (mean ± standard deviation: age, 12.44±4.76 years; diabetes duration, 4.41±3.70 years). We identified the presence of thyroid disease, celiac disease, autoimmune gastritis and adrenal autoimmunity, and retrospectively reviewed the files for presence of diabetic ketoacidosis at diagnosis.

RESULTS

Autoimmunity prevalence was 16.7% for thyroid autoimmunity, 9.5% for celiac disease, 5% for gastric autoimmunity and 8.0% for multiple autoimmunities. There were strong associations between severe acidosis at diabetes diagnosis (pH<7.10) and development of thyroid autoimmunity (odds ratio [OR], 5.34; 95% confidence interval [CI], 1.90‒15.1; p<0.001), celiac disease (OR, 5.83; 95% CI, 1.19‒28.6; p=0.013), gastric autoimmunity (OR, 13.1; 95% CI, 1.22‒140; p=0.006) and multiple autoimmunity (OR, 26.7; 95% CI, 2.36‒301; p<0.01). The associations persisted after adjustment for sex, age at diabetes diagnosis, age at assessment, time since diabetes diagnosis and antiglutamic acid decarboxylase autoantibody status.

CONCLUSIONS

The severity of acidosis at diagnosis is strongly associated with the development of associated autoimmune diseases in children with type 1 diabetes and could act as a predictive factor for multiple autoimmunity development. This association can be either due to effect of acidosis on immune system or to the presence of a more aggressive diabetes endotype.

Self-healing microcapsules synergetically modulate immunization microenvironments for potent cancer vaccination

Therapeutic cancer vaccines that harness the immune system to reject cancer cells have shown great promise for cancer treatment. Although a wave of efforts have spurred to improve the therapeutic effect, unfavorable immunization microenvironment along with a complicated preparation process and frequent vaccinations substantially compromise the performance. Here, we report a novel microcapsule-based formulation for high-performance cancer vaccinations. The special self-healing feature provides a mild and efficient paradigm for antigen microencapsulation. After vaccination, these microcapsules create a favorable immunization microenvironment in situ, wherein antigen release kinetics, recruited cell behavior, and acid surrounding work in a synergetic manner. In this case, we can effectively increase the antigen utilization, improve the antigen presentation, and activate antigen presenting cells. As a result, effective T cell response, potent tumor inhibition, antimetastatic effects, and prevention of postsurgical recurrence are achieved with various types of antigens, while neoantigen was encapsuled and evaluated in different tumor models.

The Acidic Tumor Microenvironment as a Driver of Cancer

Acidic metabolic waste products accumulate in the tumor microenvironment because of high metabolic activity and insufficient perfusion. In tumors, the acidity of the interstitial space and the relatively well-maintained intracellular pH influence cancer and stromal cell function, their mutual interplay, and their interactions with the extracellular matrix. Tumor pH is spatially and temporally heterogeneous, and the fitness advantage of cancer cells adapted to extracellular acidity is likely particularly evident when they encounter less acidic tumor regions, for instance, during invasion. Through complex effects on genetic stability, epigenetics, cellular metabolism, proliferation, and survival, the compartmentalized pH microenvironment favors cancer development. Cellular selection exacerbates the malignant phenotype, which is further enhanced by acid-induced cell motility, extracellular matrix degradation, attenuated immune responses, and modified cellular and intercellular signaling. In this review, we discuss how the acidity of the tumor microenvironment influences each stage in cancer development, from dysplasia to full-blown metastatic disease.

ASIC1a induces synovial inflammation via the Ca2+/NFATc3/ RANTES pathway

Rationale: Synovial inflammation is one of the main pathological features of rheumatoid arthritis (RA) and is a key factor leading to the progression of RA. Understanding the regulatory mechanism of synovial inflammation is crucial for the treatment of RA. Acid-sensing ion channel 1a (ASIC1a) is an H+-gated cation channel that promotes the progression of RA, but the role of ASIC1a in synovial inflammation is unclear. This study aimed to investigate whether ASIC1a is involved in the synovial inflammation and explore the underlying mechanisms in vitro and in vivo. Methods: The expression of ASIC1a and nuclear factor of activated T cells (NFATs) were analyzed by Western blotting, immunofluorescence, and immunohistochemistry both in vitro and in vivo. The Ca2+ influx mediated by ASIC1a was detected by calcium imaging and flow cytometry. The role of ASIC1a in inflammation was studied in rats with adjuvant-induced arthritis (AA). Inflammatory cytokine profile was analyzed by protein chip in RA synovial fibroblasts (RASF) and verified by a magnetic multi-cytokine assay and ELISA. The NFATc3-regulated RANTES (Regulated upon activation, normal T cell expressed and secreted) gene transcription was investigated by ChIP-qPCR and dual-luciferase reporter assay. Results: The expression of ASIC1a was significantly increased in human RA synovial tissues and primary human RASF as well as in ankle synovium of AA rats. Activated ASIC1a mediated Ca2+ influx to increase [Ca2+]i in RASF. The activation/overexpression of ASIC1a in RASF up-regulated the expression of inflammatory cytokines RANTES, sTNF RI, MIP-1a, IL-8, sTNF RII, and ICAM-1 among which RANTES was increased most remarkably. In vivo, ASIC1a promoted inflammation, synovial hyperplasia, articular cartilage, and bone destruction, leading to the progression of AA. Furthermore, activation of ASIC1a upregulated the nuclear translocation of NFATc3, which bound to RANTES promoter and directly regulated gene transcription to enhance RANTES expression. Conclusion: ASIC1a induces synovial inflammation, which leads to the progression of RA. Our study reveals a novel RA inflammation regulatory mechanism and indicates that ASIC1a might be a potential therapeutic target for RA.

Tumor Microenvironment: A Metabolic Player that Shapes the Immune Response

Immune cells survey and patrol throughout the body and sometimes take residence in niche environments with distinct cellular subtypes and nutrients that may fluctuate from those in which they matured. Rooted in immune cell physiology are metabolic pathways and metabolites that not only deliver substrates and energy for growth and survival, but also instruct effector functions and cell differentiation. Unlike cancer cells, immune cells are not subject to a "Darwinian evolutionary pressure" that would allow them to adapt to developing tumors but are often irrevocably affected to local nutrient deprivation. Thus, immune cells must metabolically adapt to these changing conditions in order to perform their necessary functions. On the other hand, there is now a growing appreciation that metabolic changes occurring in cancer cells can impact on immune cell functionality and contribute to tumor immune evasion, and as such, there is a considerable and growing interest in developing techniques that target metabolism for immunotherapy. In this review, we discuss the metabolic plasticity displayed by innate and adaptive immune cells and highlight how tumor-derived lactate and tumor acidity restrict immunity. To our knowledge, this review outlines the most recent insights on how tumor microenvironment metabolically instructs immune responsiveness.

Intelligent Metal-Phenolic Metallogels as Dressings for Infected Wounds

In this study, we report a metallogel developed based on metal-phenolic coordination of natural low-cost polyphenolic molecule and metal ions. Gelation occurs by mixing tannic acid (TA) and group (IV) titanium ions (Ti^IV) to form TA-Ti^IV gel. The TA-Ti^IV gel exhibits good capability to incorporate diverse metal ions by in situ co-gelation. Herein, five antimicrobial metal ions, i.e. ferric (Fe^III), copper (Cu^II), zinc (Zn^II), cobalt (Co^II) and nickel (Ni^II) ions, were employed to include in TA-Ti^IV gels for developing intelligent dressings for infected wounds. The chemical and coordinative structures of TA-Ti^IV metallogels were characterized by UV-Vis and Fourier-transform infrared (FT-IR) spectroscopies. Cytotoxicity of antimicrobial metallogels was explored by MTT assay with NIH 3T3 fibroblasts. The release of metal ions was evaluated by inductively coupled plasma mass spectrometry (ICP-MS), indicating the different releasing profiles upon the coordinative interactions of metal ions with TA. The formation and disassembly of metallogels are sensitive to the presence of acid and an oxidizer, H₂O₂, which are substances spontaneously generated in infected wounds due to the metabolic activity of bacteria and the intrinsic immune response. The Cu^II releasing rates of TA-Ti^IV-Cu^II metallogels at different pH values of 5.5, 7.4 and 8.5 have been studied. In addition, addition of H₂O₂ trigger fast release of Cu^II as a result of oxidation of galloyl groups in TA. Consequently, the antimicrobial potency of TA-Ti^IV-Cu^II metallogels can be simultaneously activated while the wounds are infected and healing. The antimicrobial property of metallogels against Gram-negative Escherichia coli, and Gram-positive Methicillin-Resistant Staphylococcus aureus (USA300) and Staphylococcus epidermidis has been investigated by agar diffusion test. In an animal model, the TA-Ti^IV-Cu^II metallogels were applied as dressings for infected wounds, indicating faster recovery in the wound area and extremely lower amount of bacteria around the wounds, compared to TA-Ti^IV gels and gauze. Accordingly, the intelligent nature derived metallogels is a promising and potential materials for medical applications.

Spatiotemporal pH Heterogeneity as a Promoter of Cancer Progression and Therapeutic Resistance

Dysregulation of pH in solid tumors is a hallmark of cancer. In recent years, the role of altered pH heterogeneity in space, between benign and aggressive tissues, between individual cancer cells, and between subcellular compartments, has been steadily elucidated. Changes in temporal pH-related processes on both fast and slow time scales, including altered kinetics of bicarbonate-CO₂ exchange and its effects on pH buffering and gradual, progressive changes driven by changes in metabolism, are further implicated in phenotypic changes observed in cancers. These discoveries have been driven by advances in imaging technologies. This review provides an overview of intra- and extracellular pH alterations in time and space reflected in cancer cells, as well as the available technology to study pH spatiotemporal heterogeneity.

Pro-metastatic functions of lipoproteins and extracellular vesicles in the acidic tumor microenvironment

Although the overall mortality in cancer is steadily decreasing, major groups of patients still respond poorly to available treatments. The key clinical challenge discussed here relates to the inherent capacity of cancer cells to metabolically adapt to hypoxic and acidic stress, resulting in treatment resistance and a pro-metastatic behavior. Hence, a detailed understanding of stress adaptive responses is critical for the design of more rational therapeutic strategies for cancer. We will focus on the emerging role of extracellular vesicles (EVs) and lipoprotein particles in cancer cell metabolic stress adaptation and how these pathways may constitute potential Achilles' heels of the cancer cell machinery and alternative treatment targets of metastasis. In this context, common extracellular lipid uptake mechanisms, involving specific cell-surface receptors and endocytic pathways, may operate during remodeling of acidic atherosclerotic plaques as well as the tumor microenvironment. The role of endocytosis in regulating the cellular response to hypoxic and acidic stress through spatial coordination of receptor proteins may be exploited for therapeutic purposes. As a consequence, molecular mechanisms of endocytosis have attracted increasing attention as potential targets for tumor specific delivery of therapeutic substances, such as antibody-drug conjugates. The identification of internalizing surface proteins specific to the acidic tumor niche remains an unmet need of high clinical relevance. Among the currently explored, acidosis-related, internalizing target proteins, we will focus on the cell-surface proteoglycan carbonic anhydrase 9.

Unravelling the Interplay between Extracellular Acidosis and Immune Cells

The development of an acidic tissue environment is a hallmark of a variety of inflammatory processes and solid tumors. However, little attention has been paid so far to analyze the influence exerted by extracellular pH on the immune response. Tissue acidosis (pH 6.0 to 7.0) is usually associated with the course of infectious processes in peripheral tissues. Moreover, it represents a prominent feature of solid tumors. In fact, values of pH ranging from 5.7 to 7.0 are usually found in a number of solid tumors such as breast cancer, brain tumors, sarcomas, malignant melanoma, squamous cell carcinomas, and adenocarcinomas. Both the innate and adaptive arms of the immune response appear to be finely regulated by extracellular acidosis in the range of pH values found at inflammatory sites and tumors. Low pH has been shown to delay neutrophil apoptosis, promoting their differentiation into a proangiogenic profile. Acting on monocytes and macrophages, it induces the activation of the inflammasome and the production of IL-1β, while the exposure of conventional dendritic cells to low pH promotes the acquisition of a mature phenotype. Overall, these observations suggest that high concentrations of protons could be recognized by innate immune cells as a danger-associated molecular pattern (DAMP). On the other hand, by acting on T lymphocytes, low pH has been shown to suppress the cytotoxic response mediated by CD8+ T cells as well as the production of IFN-γ by TH1 cells. Interestingly, modulation of tumor microenvironment acidity has been shown to be able not only to reverse anergy in human and mouse tumor-infiltrating T lymphocytes but also to improve the antitumor immune response induced by checkpoint inhibitors. Here, we provide an integrated view of the influence exerted by low pH on immune cells and discuss its implications in the immune response against infectious agents and tumor cells.

Novel Hydrogel-Forming Microneedle Array for Intradermal Vaccination in Mice Using Ovalbumin as a Model Protein Antigen

Global vaccination strategies have traditionally relied on the hypodermic needle and syringe model. However, to facilitate increased immunization coverage and reduce costs, novel methods of vaccine delivery are warranted. Dissolving microneedle arrays (MNs) have been proposed as an alternative approach to the hypodermic needle, offering the prospect for self-vaccination and increased immunogenicity via direct targeting of skin dendritic cells. This study, for the first time, compares the use of novel hydrogel-forming MNs and dissolving MNs for the delivery of a model protein antigen ovalbumin (OVA). We provide comparative data on both MN types in terms of in vitro characteristics and in vivo immunogenicity. Herein, both MN platforms were tested and characterized in terms of mechanical integrity and insertion properties using a validated skin insertion model. A comparative in vivo vaccination study in BALB/c mice was conducted, whereby anti-OVA specific IgG was used as a measure of delivery efficacy and subsequent immune response. While vaccination of mice with both MN platforms resulted in IgG responses, those vaccinated with dissolving MNs had significantly higher IgG titers ( p < 0.0149), despite the quantity of OVA delivered being significantly less. This study highlights the importance of MN design and the potential impact of dissolving MN polymers on the immune response to vaccine antigens. Furthermore, detailed studies are therefore required to elucidate the effects of polymer-vaccine interactions and their subsequent effect on immune responses.

Cancer Cell Metabolism: Implications for X-ray and Particle Radiation Therapy

Advances in radiation delivery technologies and immunotherapy have improved effective cancer treatments and long-term outcomes. Experimental and clinical trials have demonstrated the benefit of a combination of radiation therapy and immunotherapy for tumor eradication. Despite precise radiation dose delivery that is achievable by particle therapy and benefits from reactivating the antitumor immune response, resistance to both therapeutic strategies is frequently observed in patients. Understanding the biological origins of such resistance will create new opportunities for improved cancer treatment. Cancer metabolism and especially a high rate of aerobic glycolysis leading to overproduction and release of lactate is one such biological process favoring tumor progression and treatment resistance. Because of their known protumor effects, aerobic glycolysis and lactate production are potential targets for increased efficacy of radiation alone or in combination with immunotherapy. In the following review, we present an overview of the interplay of cancer cell lactate metabolism with the tumor microenvironment and immune cells. We discuss how a deeper understanding and careful modulation of lactate metabolism and radiation therapy might exploit this interplay for improved therapeutic outcome.

Targeting tumor-associated acidity in cancer immunotherapy

Checkpoint inhibitors, such as cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) and programmed cell death-1 (PD-1) monoclonal antibodies have changed profoundly the treatment of melanoma, renal cell carcinoma, non-small cell lung cancer, Hodgkin lymphoma, and bladder cancer. Currently, they are tested in various tumor entities as monotherapy or in combination with chemotherapies or targeted therapies. However, only a subgroup of patients benefit from checkpoint blockade (combinations). This raises the question, which all mechanisms inhibit T cell function in the tumor environment, restricting the efficacy of these immunotherapeutic approaches. Serum activity of lactate dehydrogenase, likely reflecting the glycolytic activity of the tumor cells and thus acidity within the tumor microenvironment, turned out to be one of the strongest markers predicting response to checkpoint inhibition. In this review, we discuss the impact of tumor-associated acidity on the efficacy of T cell-mediated cancer immunotherapy and possible approaches to break this barrier.

Microneedle arrays for vaccine delivery: the possibilities, challenges and use of nanoparticles as a combinatorial approach for enhanced vaccine immunogenicity

INTRODUCTION

Vaccination is one of the greatest breakthroughs of modern preventative medicine. Despite this, there remain problems surrounding delivery, efficacy and compliance. Thus, there is a pressing need to develop cost-effective vaccine delivery systems that could expand the use of vaccines, particularly within developing countries. Microneedle (MN) arrays, given their ease of use, painlessness and ability to target skin antigen presenting cells, provide an attractive platform for improved vaccine delivery and efficacy. Studies have demonstrated enhanced immunogenicity with the use of MN in comparison to conventional needle. More recently, dissolving MN have been used for efficient delivery of nanoparticles (NP), as a means to enhance antigen immunogenicity.

AREAS COVERED

This review introduces the fields of MN technology and nanotechnology, highlighting the recent advances which have been made with these two technologies combined for enhanced vaccine delivery and efficacy. Some key questions that remain to be addressed for adoption of MN in a clinical setting are also evaluated.

EXPERT OPINION

MN-mediated vaccine delivery holds potential for expanding access to vaccines, with individuals in developing countries likely to be the principal beneficiaries. The combinatorial approach of utilizing MN coupled with NP, provides opportunities to enhance the immunogenicity of vaccine antigens.

Hypoxia and acidosis: immune suppressors and therapeutic targets

Due to imbalances between vascularity and cellular growth patterns, the tumour microenvironment harbours multiple metabolic stressors including hypoxia and acidosis, which have significant influences on remodelling both tumour and peritumoral tissues. These stressors are also immunosuppressive and can contribute to escape from immune surveillance. Understanding these effects and characterizing the pathways involved can identify new targets for therapy and may redefine our understanding of traditional anti-tumour therapies. In this review, the effects of hypoxia and acidosis on tumour immunity will be summarized, and how modulating these parameters and their sequelae can be a useful tool for future therapeutic interventions is discussed.

Low pH impairs complement-dependent cytotoxicity against IgG-coated target cells

Local acidosis is a common feature of allergic, vascular, autoimmune, and cancer diseases. However, few studies have addressed the effect of extracellular pH on the immune response. Here, we analyzed whether low pH could modulate complement-dependent cytotoxicity (CDC) against IgG-coated cells. Using human serum as a complement source, we found that extracellular pH values of 5.5 and 6.0 strongly inhibit CDC against either B lymphoblast cell lines coated with the chimeric anti-CD20 mAb rituximab or PBMCs coated with the humanized anti-CD52 mAb alemtuzumab. Suppression of CDC by low pH was observed either in cells suspended in culture medium or in whole blood assays. Interestingly, not only CDC against IgG-coated cells, but also the activation of the complement system induced by the alternative and lectin pathways was prevented by low pH. Tumor-targeting mAbs represent one of the most successful tools for cancer therapy, however, the use of mAb monotherapy has only modest effects on solid tumors. Our present results suggest that severe acidosis, a hallmark of solid tumors, might impair complement-mediated tumor destruction directed by mAb.

Temperature/pH-Sensitive Nanoantibiotics and Their Sequential Assembly for Optimal Collaborations between Antibacterial and Immunoregulation

Treatment of bacterial infections due to the fast emergence of drug-resistant bacteria is a significant challenge faced in modern medicine. Here the authors report a drug-induced self-assembly nanoantibiotic for treating bacterial infection, with temperature/pH-sensitivity, synergistic antibacterial effect of silver and antibiotics, and immunoregulatory effect. In this nanoantibiotic, smart polymer p(N-isopropylacrylamide-b-acrylic acid) triblock polymer (PNA) utilized to encapsulate the drugs provides convenience in preparing this structure simply through drug-induced self-assembly and controllable release profile by changing the sequence of addition of different drugs. The polymer also allows the nanoantibiotic to be responsive to multiple external stimuli such as pH, temperature, and ionic strength. The silver and antibiotics codelivered in this nanoantibiotic can exert a synergistic antibacterial effect due to the different antibacterial mechanisms. More importantly, macrophages can be activated into an M2 phenotype to promote tissue repair by this nanoantibiotic for the negative surface charge and the antibiotics contained. The self-assembly nanoantibiotic exhibited great promise to be applied in the treatment of bacterial infection and provide favorable utility for inflammation treatment, tissue engineering, and targeted therapy.

Modulation of Dendritic Cell Apoptosis and CD8+ Cytotoxicity by Histamine: Role of Protein Kinase C

Dendritic cells (DC) are able to present extracellular antigens associated with the molecules of the major histocompatibility complex class I. In a previous work, we demonstrated that the histamine (HIS), acting through H1/H4 receptors, increases the cross-presentation of soluble ovalbumin by murine DC and can enhance the recruitment of specific CD8⁺ T lymphocytes during the development of chronic inflammatory responses. Here, we studied in more depth the mechanisms underlying this enhancement. We showed that the cytotoxicity of specific CD8⁺ lymphocytes is increased in HIS-treated DC and it is lost by inhibition of vacuolar-ATPase that prevents endosome acidification. It is known that HIS acts through G protein-coupled receptors. The H1/H4 receptors are associated with a G_q subunit, which involves PKC signaling, a pathway related to the apoptotic process. Interestingly, we demonstrated for the first time that HIS prevents DC apoptosis induced by heat shock through the inhibition of caspase-3, a mechanism dependent on PKC activation, since it is reversed by its inhibition. By contrast, cytolytic activity of T lymphocytes induced by HIS-stimulated DC was independent of PKC pathway.

Collagen I enhances the efficiency and anti-tumor activity of dendritic-tumor fusion cells

Low fusion efficiency and nominal activity of fusion cells (FCs) restrict the clinical application of dendritic cell (DC)/tumor fusion cells. Collagen I (Col I) is an interstitial collagen with a closely-knit structure used to repair damaged cell membranes. This study evaluated whether Col I could improve the fusion efficiency of polyethylene glycol (PEG)-induction and enhance the immunogenicity of fusion vaccine. DC/B16 melanoma and controlled DC/H22 hepatoma cell fusions were induced by PEG with or without Col I. Col I/PEG treatment increased the levels of DC surface molecules and the secretion of lactate, pro- and anti-inflammatory cytokines in fusion cells. Col I/PEG-treated FCs enhanced T-cell proliferation and cytotoxic T lymphocyte activity. The Col I-prepared fusion vaccine obviously suppressed tumor growth and prolonged mice survival time. Thus Col I treatment could significantly improve the efficiency of PEG-induced DC/tumor fusion and enhance the anticancer activity of the fusion vaccine. This novel fusion strategy might promote the clinical application of DC/tumor fusion immunotherapy.

B. abortus RNA is the component involved in the down-modulation of MHC-I expression on human monocytes via TLR8 and the EGFR pathway

Despite eliciting a potent CD8⁺ T cell response, Brucella abortus is able to persist and establish a chronic infection inside its host. We have previously reported that the infection of human monocytes/macrophages with B. abortus inhibits the IFN-γ-induced MHC-I cell surface expression down-modulating cytotoxic CD8⁺ T cell responses. MHC-I down-modulation depends on bacterial viability and results from the capacity of B. abortus to retain the MHC-I molecules within the Golgi apparatus. Furthermore, we recently demonstrated that epidermal growth factor receptor (EGFR) pathway is involved in this phenomenon and that this is an early event during infection. However, the components and mechanisms whereby B. abortus is able to down-modulate MHC-I remained to be elucidated. In this study we demonstrated that the down-modulation of MHC-I expression is not mediated by well-known Brucella virulence factors but instead by B. abortus RNA, a PAMP associated to viability (vita-PAMP). Surprisingly, completely degraded RNA was also able to inhibit MHC-I expression to the same extent as intact RNA. Accordingly, B. abortus RNA and its degradation products were able to mimic the MHC-I intracellular retention within the Golgi apparatus observed upon infection. We further demonstrated that TLR8, a single-stranded RNA and RNA degradation products sensor, was involved in MHC-I inhibition. On the other hand, neutralization of the EGFR reversed the MHC-I inhibition, suggesting a connection between the TLR8 and EGFR pathways. Finally, B. abortus RNA-treated macrophages display diminished capacity of antigen presentation to CD8⁺ T cells. Overall, our results indicate that the vita-PAMP RNA as well as its degradation products constitute novel virulence factors whereby B. abortus, by a TLR8-dependent mechanism and through the EGFR pathway, inhibits the IFN-γ-induced MHC-I surface expression on human monocytes/macrophages. Thus, bacteria can hide within infected cells and avoid the immunological surveillance of cytotoxic CD8⁺ T cells.

Brucella abortus is one of the intracellular bacterial species that cause brucellosis, a zoonotic worldwide disease. An intricate enigma of Brucella immunity is its long-term persistence inside host despite a vigorous and specific immune response. Our study describes a novel immune evasion strategy exploited by B. abortus: the down-modulation of the IFN-γ-induced expression of the molecules responsible for antigen presentation to CD8⁺ T cells on the surface of monocytes, Major Histocompatibility Complex Class I (MHC-I) molecules. We found that the bacterial component responsible for this phenomenon is its RNA, a component associated with bacterial viability itself. Specifically, we demonstrated that not only does intact RNA down-modulate MHC-I but also the RNA degradation products. Bacterial RNA is sensed by pattern recognition receptors (PRRs), among which TLRs family has gained more attention. In this study, we demonstrated that the receptor involved in this phenomenon is TLR8, a single-stranded RNA and RNA degradation products sensor. By means of this mechanism, Brucella impairs antigen presentation to CD8⁺ T cells, hiding within infected cells and avoiding the immunological surveillance of cytotoxic cells. On balance, these results provide new evidence to understand how B. abortus can survive inside the host and persist chronically.

Cancer acidity: An ultimate frontier of tumor immune escape and a novel target of immunomodulation

The link between cancer metabolism and immunosuppression, inflammation and immune escape has generated major interest in investigating the effects of low pH on tumor immunity. Indeed, microenvironmental acidity may differentially impact on diverse components of tumor immune surveillance, eventually contributing to immune escape and cancer progression. Although the molecular pathways underlying acidity-related immune dysfunctions are just emerging, initial evidence indicates that antitumor effectors such as T and NK cells tend to lose their function and undergo a state of mostly reversible anergy followed by apoptosis, when exposed to low pH environment. At opposite, immunosuppressive components such as myeloid cells and regulatory T cells are engaged by tumor acidity to sustain tumor growth while blocking antitumor immune responses. Local acidity could also profoundly influence bioactivity and distribution of antibodies, thus potentially interfering with the clinical efficacy of therapeutic antibodies including immune checkpoint inhibitors. Hence tumor acidity is a central regulator of cancer immunity that orchestrates both local and systemic immunosuppression and that may offer a broad panel of therapeutic targets. This review outlines the fundamental pathways of acidity-driven immune dysfunctions and sheds light on the potential strategies that could be envisaged to potentiate immune-mediated tumor control in cancer patients.

Hydrogel degradation triggered by pH for the smart release of antibiotics to combat bacterial infection

pH-Triggered smart drug release for the treatment of bacterial infection.

Keratin mediates the recognition of apoptotic and necrotic cells through dendritic cell receptor DEC205/CD205

Clearance of dead cells is critical for maintaining homeostasis and prevents autoimmunity and inflammation. When cells undergo apoptosis and necrosis, specific markers are exposed and recognized by the receptors on phagocytes. DEC205 (CD205) is an endocytotic receptor on dendritic cells with antigen presentation function and has been widely used in immune therapies for vaccine generation. It has been shown that human DEC205 recognizes apoptotic and necrotic cells in a pH-dependent fashion. However, the natural ligand(s) of DEC205 remains unknown. Here we find that keratins are the cellular ligands of human DEC205. DEC205 binds to keratins specifically at acidic, but not basic, pH through its N-terminal domains. Keratins form intermediate filaments and are important for maintaining the strength of cells and tissues. Our results suggest that keratins also function as cell markers of apoptotic and necrotic cells and mediate a pH-dependent pathway for the immune recognition of dead cells.

The choice of dialysate bicarbonate: do different concentrations make a difference?

Metabolic acidosis is a common complication of chronic kidney disease; it is typically caused by the accumulation of sulfate, phosphorus, and organic anions. Metabolic acidosis is correlated with several adverse outcomes, such as morbidity, hospitalization, and mortality. Thus, correction of metabolic acidosis is fundamental for the adequate management of many systemic complications of chronic kidney disease. In patients undergoing hemodialysis, acid-base homeostasis depends on many factors including the following: net acid production, amount of alkali given by the dialysate bath, duration of the interdialytic period, and residual diuresis, if any. Recent literature data suggest that the development of metabolic alkalosis after dialysis may contribute to adverse clinical outcomes. Our review is focused on the potential effects of different dialysate bicarbonate concentrations on hard outcomes such as mortality. Unfortunately, no randomized studies exist about this issue. Acid-base equilibrium is a complex and vital system whose regulation is impaired in chronic kidney disease. We await further studies to assess the extent to which acid-base status is a major determinant of overall survival in patients undergoing hemodialysis. For the present, the clinician should understand that target values for predialysis serum bicarbonate concentration have been established primarily based on observational studies and expert opinion. Based on this, we should keep the predialysis serum bicarbonate level at least at 22 mmol/l. Furthermore, a specific focus should be addressed by the attending nephrologist to the clinical and nutritional status of the major outliers on both the acid and alkaline sides of the curve.