Reconstitution of bactericidal activity in chronic granulomatous disease cells by glucose-oxidase-containing liposomes

Staphylococcus aureus senses human neutrophils via PerR to coordinate the expression of the toxin LukAB

Staphylococcus aureus is a gram-positive pathogen that poses a major health concern, in part due to its large array of virulence factors that allow infection and evasion of the immune system. One of these virulence factors is the bicomponent pore-forming leukocidin LukAB. The regulation of lukAB expression is not completely understood, especially in the presence of immune cells such as human polymorphonuclear neutrophils (hPMNs). Here, we screened for transcriptional regulators of lukAB during the infection of primary hPMNs. We uncovered that PerR, a peroxide sensor, is vital for hPMN-mediated induction of lukAB and that PerR upregulates cytotoxicity during the infection of hPMNs. Exposure of S. aureus to hydrogen peroxide (H2O2) alone also results in increased lukAB promoter activity, a phenotype dependent on PerR. Collectively, our data suggest that S. aureus uses PerR to sense the H2O2 produced by hPMNs to stimulate the expression of lukAB, allowing the bacteria to withstand these critical innate immune cells.IMPORTANCEStaphylococcus aureus utilizes a diverse set of virulence factors, such as leukocidins, to subvert human neutrophils, but how these toxins are regulated is incompletely defined. Here, we identified the peroxide-sensitive repressor, PerR, as a required protein involved in the induction of lukAB in the presence of primary human neutrophils, a phenotype directly linked to the ability of PerR to sense H2O2. Thus, we show that S. aureus coordinates sensing and resistance to oxidative stress with toxin production to promote pathogen survival.

Superoxide: The enigmatic chemical chameleon in neutrophil biology

The burst of superoxide produced when neutrophils phagocytose bacteria is the defining biochemical feature of these abundant immune cells. But 50 years since this discovery, the vital role superoxide plays in host defense has yet to be defined. Superoxide is neither bactericidal nor is it just a source of hydrogen peroxide. This simple free radical does, however, have remarkable chemical dexterity. Depending on its environment and reaction partners, superoxide can act as an oxidant, a reductant, a nucleophile, or an enzyme substrate. We outline the evidence that inside phagosomes where neutrophils trap, kill, and digest bacteria, superoxide will react preferentially with the enzyme myeloperoxidase, not the bacterium. By acting as a cofactor, superoxide will sustain hypochlorous acid production by myeloperoxidase. As a substrate, superoxide may give rise to other forms of reactive oxygen. We contend that these interactions hold the key to understanding the precise role superoxide plays in neutrophil biology. State-of-the-art techniques in mass spectrometry, oxidant-specific fluorescent probes, and microscopy focused on individual phagosomes are needed to identify bactericidal mechanisms driven by superoxide. This work will undoubtably lead to fascinating discoveries in host defense and give a richer understanding of superoxide's varied biology.

Pondering neutrophil extracellular traps with healthy skepticism

The authors engage in a dialogue that evaluates critically the state of the study of neutrophil extracellular traps (NETs), a phenomenon currently the object of considerable interest, with the goal of identifying those aspects that merit clarification in order to assign the process its proper place in our current understanding of cell biology. Since the seminal observations in the Zychlinsky laboratory that described the extrusion of filaments of nuclear DNA associated with histones and granule proteins from neutrophils stimulated in vitro, many investigators have examined the phenomenon of NET formation in numerous and diverse settings. However, an overview of work in this rapidly growing field prompts several fundamental questions about NETs, including their precise composition, the mechanisms by which they arise, their clinical relevance, and the interrelationship of those observed in vitro and in vivo. In this discussion, the authors challenge interpretation of data from some experimental settings and provide recommendations for specific studies that would address the concerns raised, improve understanding of the biological relevance of NETs, and strengthen the field.

Neutrophil-generated oxidative stress and protein damage in Staphylococcus aureus

Staphylococcus aureus is a ubiquitous, versatile and dangerous pathogen. It colonizes over 30% of the human population, and is one of the leading causes of death by an infectious agent. During S. aureus colonization and invasion, leukocytes are recruited to the site of infection. To combat S. aureus, leukocytes generate an arsenal of reactive species including superoxide, hydrogen peroxide, nitric oxide and hypohalous acids that modify and inactivate cellular macromolecules, resulting in growth defects or death. When S. aureus colonization cannot be cleared by the immune system, antibiotic treatment is necessary and can be effective. Yet, this organism quickly gains resistance to each new antibiotic it encounters. Therefore, it is in the interest of human health to acquire a deeper understanding of how S. aureus evades killing by the immune system. Advances in this field will have implications for the design of future S. aureus treatments that complement and assist the host immune response. In that regard, this review focuses on how S. aureus avoids host-generated oxidative stress, and discusses the mechanisms used by S. aureus to survive oxidative damage including antioxidants, direct repair of damaged proteins, sensing oxidant stress and transcriptional changes. This review will elucidate areas for studies to identify and validate future antimicrobial targets.

Staphylococcus aureus SaeR/S-regulated factors reduce human neutrophil reactive oxygen species production

Neutrophils are the first line of defense after a pathogen has breached the epithelial barriers, and unimpaired neutrophil functions are essential to clear infections. Staphylococcus aureus is a prevalent human pathogen that is able to withstand neutrophil killing, yet the mechanisms used by S. aureus to inhibit neutrophil clearance remain incompletely defined. The production of reactive oxygen species (ROS) is a vital neutrophil antimicrobial mechanism. Herein, we test the hypothesis that S. aureus uses the SaeR/S two-component gene regulatory system to produce virulence factors that reduce neutrophil ROS production. With the use of ROS probes, the temporal and overall production of neutrophil ROS was assessed during exposure to the clinically relevant S. aureus USA300 (strain LAC) and its isogenic mutant LACΔsaeR/S Our results demonstrated that SaeR/S-regulated factors do not inhibit neutrophil superoxide (O₂^-) production. However, subsequent neutrophil ROS production was significantly reduced during exposure to LAC compared with LACΔsaeR/S In addition, neutrophil H₂O₂ production was reduced significantly by SaeR/S-regulated factors by a mechanism independent of catalase. Consequently, the reduction in neutrophil H₂O₂ resulted in decreased production of the highly antimicrobial agent hypochlorous acid/hypochlorite anion (HOCl/^-OCl). These findings suggest a new evasion strategy used by S. aureus to diminish a vital neutrophil antimicrobial mechanism.

NOX2 As a Target for Drug Development: Indications, Possible Complications, and Progress

SIGNIFICANCE

NOX2 is important for host defense, and yet is implicated in a large number of diseases in which inflammation plays a role in pathogenesis. These include acute and chronic lung inflammatory diseases, stroke, traumatic brain injury, and neurodegenerative diseases, including Alzheimer's and Parkinson's Diseases.

RECENT ADVANCES

Recent drug development programs have targeted several NOX isoforms that are implicated in a variety of diseases. The focus has been primarily on NOX4 and NOX1 rather than on NOX2, due, in part, to concerns about possible immunosuppressive side effects. Nevertheless, NOX2 clearly contributes to the pathogenesis of many inflammatory diseases, and its inhibition is predicted to provide a novel therapeutic approach.

CRITICAL ISSUES

Possible side effects that might arise from targeting NOX2 are discussed, including the possibility that such inhibition will contribute to increased infections and/or autoimmune disorders. The state of the field with regard to existing NOX2 inhibitors and targeted development of novel inhibitors is also summarized.

FUTURE DIRECTIONS

NOX2 inhibitors show particular promise for the treatment of inflammatory diseases, both acute and chronic. Theoretical side effects include pro-inflammatory and autoimmune complications and should be considered in any therapeutic program, but in our opinion, available data do not indicate that they are sufficiently likely to eliminate NOX2 as a drug target, particularly when weighed against the seriousness of many NOX2-related indications. Model studies demonstrating efficacy with minimal side effects are needed to encourage future development of NOX2 inhibitors as therapeutic agents.

Insights into primary immune deficiency from quantitative microscopy

Recent advances in genomics-based technology have resulted in an increase in our understanding of the molecular basis of many primary immune deficiencies. Along with this increased knowledge comes an increased responsibility to understand the underlying mechanism of disease, and thus increasingly sophisticated technologies are being used to investigate the cell biology of human immune deficiencies. One such technology, which has itself undergone a recent explosion in innovation, is that of high-resolution microscopy and image analysis. These advances complement innovative studies that have previously shed light on critical cell biological processes that are perturbed by single-gene mutations in primary immune deficiency. Here we highlight advances made specifically in the following cell biological processes: (1) cytoskeletal-related processes; (2) cell signaling; (3) intercellular trafficking; and (4) cellular host defense.

Neutrophils: Between host defence, immune modulation, and tissue injury

Neutrophils, the most abundant human immune cells, are rapidly recruited to sites of infection, where they fulfill their life-saving antimicrobial functions. While traditionally regarded as short-lived phagocytes, recent findings on long-term survival, neutrophil extracellular trap (NET) formation, heterogeneity and plasticity, suppressive functions, and tissue injury have expanded our understanding of their diverse role in infection and inflammation. This review summarises our current understanding of neutrophils in host-pathogen interactions and disease involvement, illustrating the versatility and plasticity of the neutrophil, moving between host defence, immune modulation, and tissue damage.

Redox reactions and microbial killing in the neutrophil phagosome

SIGNIFICANCE

When neutrophils kill microorganisms, they ingest them into phagosomes and bombard them with a burst of reactive oxygen species.

RECENT ADVANCES

This review focuses on what oxidants are produced and how they kill. The neutrophil NADPH oxidase is activated and shuttles electrons from NADPH in the cytoplasm to oxygen in the phagosomal lumen. Superoxide is generated in the narrow space between the ingested organism and the phagosomal membrane and kinetic modeling indicates that it reaches a concentration of around 20 μM. Degranulation leads to a very high protein concentration with up to millimolar myeloperoxidase (MPO). MPO has many substrates, but its main phagosomal reactions should be to dismutate superoxide and, provided adequate chloride, catalyze efficient conversion of hydrogen peroxide to hypochlorous acid (HOCl). Studies with specific probes have shown that HOCl is produced in the phagosome and reacts with ingested bacteria. The amount generated should be high enough to kill. However, much of the HOCl reacts with phagosomal proteins. Generation of chloramines may contribute to killing, but the full consequences of this are not yet clear.

CRITICAL ISSUES

Isolated neutrophils kill most of the ingested microorganisms rapidly by an MPO-dependent mechanism that is almost certainly due to HOCl. However, individuals with MPO deficiency rarely have problems with infection. A possible explanation is that HOCl provides a frontline response that kills most of the microorganisms, with survivors killed by nonoxidative processes. The latter may deal adequately with low-level infection but with high exposure, more efficient HOCl-dependent killing is required.

FUTURE DIRECTIONS

Better quantification of HOCl and other oxidants in the phagosome should clarify their roles in antimicrobial action.

Myeloperoxidase: a front-line defender against phagocytosed microorganisms

Successful immune defense requires integration of multiple effector systems to match the diverse virulence properties that members of the microbial world might express as they initiate and promote infection. Human neutrophils--the first cellular responders to invading microbes--exert most of their antimicrobial activity in phagosomes, specialized membrane-bound intracellular compartments formed by ingestion of microorganisms. The toxins generated de novo by the phagocyte NADPH oxidase and delivered by fusion of neutrophil granules with nascent phagosomes create conditions that kill and degrade ingested microbes. Antimicrobial activity reflects multiple and complex synergies among the phagosomal contents, and optimal action relies on oxidants generated in the presence of MPO. The absence of life-threatening infectious complications in individuals with MPO deficiency is frequently offered as evidence that the MPO oxidant system is ancillary rather than essential for neutrophil-mediated antimicrobial activity. However, that argument fails to consider observations from humans and KO mice that demonstrate that microbial killing by MPO-deficient cells is less efficient than that of normal neutrophils. We present evidence in support of MPO as a major arm of oxidative killing by neutrophils and propose that the essential contribution of MPO to normal innate host defense is manifest only when exposure to pathogens overwhelms the capacity of other host defense mechanisms.

Clearance of apoptotic neutrophils is diminished in cord blood monocytes and does not lead to reduced IL-8 production

Phagocytosis of apoptotic cells, e.g., neutrophils, by monocytes is essential for resolution of inflammation. Delayed removal leads to secondary necrosis, perpetuating inflammation, and tissue destruction. Common histologic features in neonatal chronic inflammatory disorders are an accumulation of apoptotic cells in inflamed tissues. We hypothesized that apoptotic cell removal by monocytes is compromised in newborns. PKH-26 labeled autologous or allogeneic apoptotic neutrophils were fed to monocytes of adult donors (PBMO) and cord blood (CBMO), and phagocytic activity was analyzed by flow cytometry and confocal microscopy. Relative mRNA-expression levels of 21 surface receptors and bridging molecules relevant for apoptotic cell removal were measured, as was postphagocytic IL-8 production upon LPS-stimulation. Compared with PBMO, CBMO exhibited a significantly diminished phagocytotic competence for autologous and allogeneic apoptotic neutrophils. mRNA-expression levels of milk fat globule-EGF factor 8 and T cell immunoglobulin- and mucin-domain-containing molecule, two crucial members of the phagocytic synapse of apoptotic cell removal, were reduced in CBMO. In PBMO, interaction with autologous apoptotic neutrophils reduced LPS-induced IL-8 production whereas it was enhanced in CBMO. Our data suggest a specific defect in CBMO during clearance of apoptotic neutrophils resulting in impaired anti-inflammatory capacity.

How human neutrophils kill and degrade microbes: an integrated view

Neutrophils constitute the dominant cell in the circulation that mediates the earliest innate immune human responses to infection. The morbidity and mortality from infection rise dramatically in patients with quantitative or qualitative neutrophil defects, providing clinical confirmation of the important role of normal neutrophils for human health. Neutrophil-dependent anti-microbial activity against ingested microbes represents the collaboration of multiple agents, including those prefabricated during granulocyte development in the bone marrow and those generated de novo following neutrophil activation. Furthermore, neutrophils cooperate with extracellular agents as well as other immune cells to optimally kill and degrade invading microbes. This brief review focuses attention on two examples of the integrated nature of neutrophil-mediated anti-microbial action within the phagosome. The importance and complexity of myeloperoxidase-mediated events illustrate a collaboration of anti-microbial responses that are endogenous to the neutrophil, whereas the synergy between the phagocyte NADPH (nicotinamide adenine dinucleotide phosphate) oxidase and plasma-derived group IIA phospholipase A(2) exemplifies the collective effects of the neutrophil with an exogenous factor to achieve degradation of ingested staphylococci.

Liver-homing of purified glucose oxidase: a novel in vivo model of physiological hepatic oxidative stress (H2O2)

BACKGROUND/AIMS

Reactive oxygen species (ROS), such as H2O2, are implicated in normal and pathological liver function. However, due to the lack of suitable in vivo models of ROS generation the (patho) physiological relevance of H2O2 remains controversial.

METHODS

We established a novel model of sustained hepatic H2O2 release using intravenous administration of purified Aspergillus niger glucose oxidase (GOX) in rats.

RESULTS

GOX is rapidly cleared from the blood stream and almost exclusively localizes to Kupffer cells. GOX maintained its ability to generate H2O2 over 24h. While sublethal GOX doses induced hepatocellular necrosis, our morphological and functional studies show that lower levels of GOX which generate H2O2 comparable to release by inflammatory cells are non-toxic and do not induce histological inflammation. However, these non-toxic H2O2 levels increased oxidized glutathione and induced heme oxygenase 1 in the liver. In addition, several hepatocyte transporters were downregulated, while no decrease of bile formation, a sensitive marker of liver function, was observed.

CONCLUSIONS

Our in vivo model allows to study the effects of extracellular H2O2 in the liver as is released by inflammatory cells. Thus analysis of the role of this major ROS in the absence of confounding inflammatory cofactors will be possible.

The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases. These enzymes share the capacity to transport electrons across the plasma membrane and to generate superoxide and other downstream reactive oxygen species (ROS). Activation mechanisms and tissue distribution of the different members of the family are markedly different. The physiological functions of NOX family enzymes include host defense, posttranlational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. NOX enzymes also contribute to a wide range of pathological processes. NOX deficiency may lead to immunosuppresion, lack of otoconogenesis, or hypothyroidism. Increased NOX activity also contributes to a large number or pathologies, in particular cardiovascular diseases and neurodegeneration. This review summarizes the current state of knowledge of the functions of NOX enzymes in physiology and pathology.

Tresylated PEG-sterols for coupling of proteins to preformed plain or PEGylated liposomes

A simple and inexpensive method for functionalization of preformed liposomes is presented. Soy sterol-PEG1300 ethers are activated by tresylation at the end of the PEG chain. Coupling of bovine serum albumin as an amino group containing model ligand to the activated lipids can be performed at pH 8.4 with high efficiency. At room temperature, the mixture of sterol-PEG and sterol-PEG-protein inserts rapidly into the outer liposome monolayer with high efficiency (>100 microg protein/mumol total lipid). This method of post-functionalization is shown to be effective with fluid or rigid and plain or pre-PEGylated liposomes (EPC/Chol, 7:3; HSPC/Chol 2:1, and EPC/Chol/MPEG2000-DSPE 2:1:0.16 molar ratios). The release of entrapped calcein upon the insertion of 7.5 mol% of the functionalized sterols is lower than 4%. Incubation of post-functionalized liposomes with serum for 20 h at 37 degrees C shows stable protein attachment at the liposome surface.

Common methodology is inadequate for studies on the microbicidal activity of neutrophils

Microbicidal activity of neutrophils is usually measured by colony-counting techniques after cell lysis in distilled water. While studying the effect of the reduced nicotinamide adenine dinucleotide phosphate-oxidase inhibitor diphenyleneiodonium (DPI) on the staphylocidal activity of neutrophils, we obtained inconsistent results: various degrees of inhibition in some experiments and no effect in others. The lysis step, i.e., dilution of neutrophils in distilled water, was the source of error. Cell-associated microorganisms were not dispersed effectively by this treatment. We overcame this problem by using water at pH 11 for cell lysis. Under these conditions, killing was inhibited completely and reproducibly by DPI. Here, we show that cell lysis in distilled water is incomplete and leads to an overestimate of microbial killing. This hinders identification of partial defects and makes complete defects appear as partial. We found that DPI-treated neutrophils and chronic granulomatous disease neutrophils were completely defective in killing of Staphylococcus aureus and Candida albicans and partially defective in killing of Escherichia coli after lysis with water pH 11, whereas after lysis in distilled water, killing of S. aureus and C. albicans was approximately 60% and approximately 70% of control killing, respectively, and killing of E. coli was normal. Likewise, killing of S. aureus by myeloperoxidase-deficient neutrophils was severely impaired after lysis in water pH 11 but appeared normal after lysis in distilled water. As most studies about neutrophil microbicidal activity have been performed using distilled water, our findings indicate that previous data about killing defects and the effects of agents that modulate microbicidal activity of neutrophils should be re-evaluated.

How neutrophils kill microbes

Neutrophils provide the first line of defense of the innate immune system by phagocytosing, killing, and digesting bacteria and fungi. Killing was previously believed to be accomplished by oxygen free radicals and other reactive oxygen species generated by the NADPH oxidase, and by oxidized halides produced by myeloperoxidase. We now know this is incorrect. The oxidase pumps electrons into the phagocytic vacuole, thereby inducing a charge across the membrane that must be compensated. The movement of compensating ions produces conditions in the vacuole conducive to microbial killing and digestion by enzymes released into the vacuole from the cytoplasmic granules.

Myeloperoxidase: friend and foe

Neutrophilic polymorphonuclear leukocytes (neutrophils) are highly specialized for their primary function, the phagocytosis and destruction of microorganisms. When coated with opsonins (generally complement and/or antibody), microorganisms bind to specific receptors on the surface of the phagocyte and invagination of the cell membrane occurs with the incorporation of the microorganism into an intracellular phagosome. There follows a burst of oxygen consumption, and much, if not all, of the extra oxygen consumed is converted to highly reactive oxygen species. In addition, the cytoplasmic granules discharge their contents into the phagosome, and death of the ingested microorganism soon follows. Among the antimicrobial systems formed in the phagosome is one consisting of myeloperoxidase (MPO), released into the phagosome during the degranulation process, hydrogen peroxide (H2O2), formed by the respiratory burst and a halide, particularly chloride. The initial product of the MPO-H2O2-chloride system is hypochlorous acid, and subsequent formation of chlorine, chloramines, hydroxyl radicals, singlet oxygen, and ozone has been proposed. These same toxic agents can be released to the outside of the cell, where they may attack normal tissue and thus contribute to the pathogenesis of disease. This review will consider the potential sources of H2O2 for the MPO-H2O2-halide system; the toxic products of the MPO system; the evidence for MPO involvement in the microbicidal activity of neutrophils; the involvement of MPO-independent antimicrobial systems; and the role of the MPO system in tissue injury. It is concluded that the MPO system plays an important role in the microbicidal activity of phagocytes.

Liposomes and blood cells: a flow cytometric study

To clarify the interactions of liposomes with blood cells, this study examined the behaviour of liposomes of a range of compositions in the presence of purified human blood cells in buffer or plasma; or in whole blood, or in mice in vivo. Liposomes, labeled with the hydrophilic fluorochrome, carboxy fluorescein (CF), or with membrane-sequestering R18 or FITC-labeled phospholipids, were mixed with blood cells and the appearance of the fluorochromes in the blood cell population was monitored by flow cytometry. Irrespective of composition, with or without poly(ethylene glycol), all types of liposomes were found to interact rapidly and dose-dependently with red cells, leukocytes and platelets, both in vitro and in vivo. This took place equally in the presence and the absence of plasma proteins and functional enzyme cascades, suggesting that the prime facie interaction is opsonization-independent and is consistent with liposome-blood cell fusion.

The Potential Role of Neutrophils in Promoting the Metastatic Phenotype of Tumors Releasing Interleukin-8

In the last decade, several groups have shown a direct correlation between the inappropriate or ectopic release of interleukin (IL)-8 by tumor cells in vitro and their growth and metastatic potential using in vivo models of tumor growth. IL-8 is a potent neutrophil chemoattractant. Neutrophils, as "early responders" to wounds and infections, release enzymes to remodel the extracellular matrix of the tissues through which they migrate to reach the site of the wound or infection. It is proposed that the host's cellular response to IL-8 released by tumor cells enhances angiogenesis and contributes to tumor growth and progression. The activities released by the responding neutrophils could serve as enablers of tumor cell migration through the extracellular matrix, helping them enter the vasculature and journey to new, metastatic sites. The reactive oxygen species produced by neutrophilic oxidases to kill invading organisms have the potential to interact with tumor cells to attenuate their apoptotic cascade and increase their mutational rate. It is proposed that the increase in metastatic potential of tumors ectopically releasing IL-8 is, in part, attributable to their ability to attract neutrophils. Discussed here are possible mechanisms by which the neutrophils responding to ectopic IL-8 contribute to the in vivo growth, progression, and metastatic potential of tumor cells. Possible targets are also presented for the development of therapies to attenuate the effects of the ectopic IL-8 release by tumor cells.

Glucose-oxidase based self-destructing polymeric vesicles

We have designed oxidation-responsive vesicles from synthetic amphiphilic block copolymers ("polymersomes") of ethylene glycol and propylene sulfide. Thioethers in the hydrophobic poly(propylene sulfide) block are converted into the more hydrophilic sulfoxides and sulfones upon exposure to an oxidative environment, changing the hydrophilic-lipophilic balance of the macroamphiphile and thus inducing its solubilization. Here we sought to explore generation of the oxidative environment and induction of polymersome destabilization through production of hydrogen peroxide by the glucose-oxidase (GOx)/glucose/oxygen system. We studied the encapsulation of GOx within polymersomes, its stability and activity, and glucose-triggered polymersome destabilization. Stimulus-responsive polymersomes may find applications as nanocontainers in sensing devices and as drug delivery systems.

Current treatment options for chronic granulomatous disease

Chronic granulomatous disease is a rare inherited disorder of phagocytic cells which results in a susceptibility to infections of catalase-positive bacteria and fungi (especially Aspergillus species), as well as granuloma formation. The mainstay of therapy is antibacterial and antifungal prophylaxis. Trimethoprim sulfamethoxazole is the drug of choice for the prevention of bacterial infection, while itraconazole is most widely used for the prevention of fungal infection. Immunomodulatory agents, such as IFN-phi, have a role in the prevention and treatment of intractable infection. New antifungal agents provide the promise of improved cure rates for invasive Aspergillus, while bone marrow transplants and gene therapy may offer the promise of complete cure.