Belimumab in kidney transplantation: an experimental medicine, randomised, placebo-controlled phase 2 trial.

BACKGROUND: B cells produce alloantibodies and activate alloreactive T cells, negatively affecting kidney transplant survival. By contrast, regulatory B cells are associated with transplant tolerance. Immunotherapies are needed that inhibit B-cell effector function, including antibody secretion, while sparing regulators and minimising infection risk. B lymphocyte stimulator (BLyS) is a cytokine that promotes B-cell activation and has not previously been targeted in kidney transplant recipients. We aimed to determine the safety and activity of an anti-BLyS antibody, belimumab, in addition to standard-of-care immunosuppression in adult kidney transplant recipients. We used an experimental medicine study design with multiple secondary and exploratory endpoints to gain further insight into the effect of belimumab on the generation of de-novo IgG and on the regulatory B-cell compartment. METHODS: We undertook a double-blind, randomised, placebo-controlled phase 2 trial of belimumab, in addition to standard-of-care immunosuppression (basiliximab, mycophenolate mofetil, tacrolimus, and prednisolone) at two centres, Addenbrooke's Hospital, Cambridge, UK, and Guy's and St Thomas' Hospital, London, UK. Participants were eligible if they were aged 18-75 years and receiving a kidney transplant and were planned to receive standard-of-care immunosuppression. Participants were randomly assigned (1:1) to receive either intravenous belimumab 10 mg per kg bodyweight or placebo, given at day 0, 14, and 28, and then every 4 weeks for a total of seven infusions. The co-primary endpoints were safety and change in the concentration of naive B cells from baseline to week 24, both of which were analysed in all patients who received a transplant and at least one dose of drug or placebo (the modified intention-to-treat [mITT] population). This trial has been completed and is registered with ClinicalTrials.gov, NCT01536379, and EudraCT, 2011-006215-56. FINDINGS: Between Sept 13, 2013, and Feb 8, 2015, of 303 patients assessed for eligibility, 28 kidney transplant recipients were randomly assigned to receive belimumab (n=14) or placebo (n=14). 25 patients (12 [86%] patients assigned to the belimumab group and 13 [93%] patients assigned to the placebo group) received a transplant and were included in the mITT population. We observed similar proportions of adverse events in the belimumab and placebo groups, including serious infections (one [8%] of 12 in the belimumab group and five [38%] of 13 in the placebo group during the 6-month on-treatment phase; and none in the belimumab group and two [15%] in the placebo group during the 6-month follow-up). In the on-treatment phase, one patient in the placebo group died because of fatal myocardial infarction and acute cardiac failure. The co-primary endpoint of a reduction in naive B cells from baseline to week 24 was not met. Treatment with belimumab did not significantly reduce the number of naive B cells from baseline to week 24 (adjusted mean difference between the belimumab and placebo treatment groups -34·4 cells per µL, 95% CI -109·5 to 40·7). INTERPRETATION: Belimumab might be a useful adjunct to standard-of-care immunosuppression in renal transplantation, with no major increased risk of infection and potential beneficial effects on humoral alloimmunity. FUNDING: GlaxoSmithKline.

Different Candida parapsilosis clinical isolates and lipase deficient strain trigger an altered cellular immune response.

Numerous human diseases can be associated with fungal infections either as potential causative agents or as a result of changed immune status due to a primary disease. Fungal infections caused by Candida species can vary from mild to severe dependent upon the site of infection, length of exposure, and past medical history. Patients with impaired immune status are at increased risk for chronic fungal infections. Recent epidemiologic studies have revealed the increasing incidence of candidiasis caused by non-albicans species such as Candida parapsilosis. Due to its increasing relevance we chose two distinct C. parapsilosis strains, to describe the cellular innate immune response toward this species. In the first section of our study we compared the interaction of CLIB 214 and GA1 cells with murine and human macrophages. Both strains are commonly used to investigate C. parapsilosis virulence properties. CLIB 214 is a rapidly pseudohyphae-forming strain and GA1 is an isolate that mainly exists in a yeast form. Our results showed, that the phagocyte response was similar in terms of overall uptake, however differences were observed in macrophage migration and engulfment of fungal cells. As C. parapsilosis releases extracellular lipases in order to promote host invasion we further investigated the role of these secreted components during the distinct stages of the phagocytic process. Using a secreted lipase deficient mutant strain and the parental strain GA1 individually and simultaneously, we confirmed that fungal secreted lipases influence the fungi's virulence by detecting altered innate cellular responses. In this study we report that two isolates of a single species can trigger markedly distinct host responses and that lipase secretion plays a role on the cellular level of host-pathogen interactions.

Rab14 regulates maturation of macrophage phagosomes containing the fungal pathogen Candida albicans and outcome of the host-pathogen interaction.

Avoidance of innate immune defense is an important mechanism contributing to the pathogenicity of microorganisms. The fungal pathogen Candida albicans undergoes morphogenetic switching from the yeast to the filamentous hyphal form following phagocytosis by macrophages, facilitating its escape from the phagosome, which can result in host cell lysis. We show that the intracellular host trafficking GTPase Rab14 plays an important role in protecting macrophages from lysis mediated by C. albicans hyphae. Live-cell imaging of macrophages expressing green fluorescent protein (GFP)-tagged Rab14 or dominant negative Rab14, or with small interfering RNA (siRNA)-mediated knockdown of Rab14, revealed the temporal dynamics of this protein and its influence on the maturation of macrophage phagosomes following the engulfment of C. albicans cells. Phagosomes containing live C. albicans cells became transiently Rab14 positive within 2 min following engulfment. The duration of Rab14 retention on phagosomes was prolonged for hyphal cargo and was directly proportional to hyphal length. Interference with endogenous Rab14 did not affect the migration of macrophages toward C. albicans cells, the rate of engulfment, the overall uptake of fungal cells, or early phagosome processing. However, Rab14 depletion delayed the acquisition of the late phagosome maturation markers LAMP1 and lysosomal cathepsin, indicating delayed formation of a fully bioactive lysosome. This was associated with a significant increase in the level of macrophage killing by C. albicans. Therefore, Rab14 activity promotes phagosome maturation during C. albicans infection but is dysregulated on the phagosome in the presence of the invasive hyphal form, which favors fungal survival and escape.

Novel insights into host-fungal pathogen interactions derived from live-cell imaging.

The theoretical physicist and Nobel laureate Richard Feynman outlined in his 1959 lecture, "There's plenty of room at the bottom", the enormous possibility of producing and visualising things at smaller scales. The advent of advanced scanning and transmission electron microscopy and high-resolution microscopy has begun to open the door to visualise host-pathogen interactions at smaller scales, and spinning disc confocal and two-photon microscopy has improved our ability to study these events in real time in three dimensions. The aim of this review is to illustrate some of the advances in understanding host-fungal interactions that have been made in recent years in particular those relating to the interactions of live fungal pathogens with phagocytes. Dynamic imaging of host-pathogen interactions has recently revealed novel detail and unsuspected mechanistic insights, facilitating the dissection of the phagocytic process into its component parts. Here, we will highlight advances in our knowledge of host-fungal pathogen interactions, including the specific effects of fungal cell viability, cell wall composition and morphogenesis on the phagocytic process and try to define the relative contributions of neutrophils and macrophages to the clearance of fungal pathogens in vitro and the infected host.

Kinetic studies of Candida parapsilosis phagocytosis by macrophages and detection of intracellular survival mechanisms.

Even though the number of Candida infections due to non-albicans species like C. parapsilosis has been increasing, little is known about their pathomechanisms. Certain aspects of C. parapsilosis and host interactions have already been investigated; however we lack information about the innate cellular responses toward this species. The aim of our project was to dissect and compare the phagocytosis of C. parapsilosis to C. albicans and to another Candida species C. glabrata by murine and human macrophages by live cell video microscopy. We broke down the phagocytic process into three stages: macrophage migration, engulfment of fungal cells and host cell killing after the uptake. Our results showed increased macrophage migration toward C. parapsilosis and we observed differences during the engulfment processes when comparing the three species. The engulfment time of C. parapsilosis was comparable to that of C. albicans regardless of the pseudohypha length and spatial orientation relative to phagocytes, while the rate of host cell killing and the overall uptake regarding C. parapsilosis showed similarities mainly with C. glabrata. Furthermore, we observed difference between human and murine phagocytes in the uptake of C. parapsilosis. UV-treatment of fungal cells had varied effects on phagocytosis dependent upon which Candida strain was used. Besides statistical analysis, live cell imaging videos showed that this species similarly to the other two also has the ability to survive in host cells via the following mechanisms: yeast replication, and pseudohypha growth inside of phagocytes, exocytosis of fungal cells and also abortion of host cell mitosis following the uptake. According to our knowledge this is the first study that provides a thorough examination of C. parapsilosis phagocytosis and reports intracellular survival mechanisms associated with this species.

Rapid recovery of membrane cofactor protein (MCP; CD46) associated atypical haemolytic uraemic syndrome with plasma exchange.

Atypical haemolytic uraemic syndrome (aHUS), unlike typical HUS is due to complement dysregulation. At least one abnormality of the complement system can be identified in 70% of patients. aHUS is associated with a poor prognosis with 25% mortality and 50% progress to end-stage renal disease. Genetic abnormalities in the complement system, proteins including CFH, CFI, CFB, C3, CFHR1/3 and MCP (CD46) lead to uncontrolled complement activation in aHUS. We presented the second reported case of aHUS associated with a heterozygous c.191G > T mutation in exon 2 of MCP who responded rapidly to plasma exchange.

Ybp1 and Gpx3 signaling in Candida albicans govern hydrogen peroxide-induced oxidation of the Cap1 transcription factor and macrophage escape.

AIMS: As Candida albicans is the major fungal pathogen of humans, there is an urgent need to understand how this pathogen evades toxic reactive oxygen species (ROS) generated by the host immune system. A key regulator of antioxidant gene expression, and thus ROS resistance, in C. albicans is the AP-1-like transcription factor Cap1. Despite this, little is known regarding the intracellular signaling mechanisms that underlie the oxidation and activation of Cap1. Therefore, the aims of this study were; (i) to identify the regulatory proteins that govern Cap1 oxidation, and (ii) to investigate the importance of Cap1 oxidation in C. albicans pathogenesis. RESULTS: In response to hydrogen peroxide (H2O2), but not glutathione-depleting/modifying oxidants, Cap1 oxidation, nuclear accumulation, phosphorylation, and Cap1-dependent gene expression, is mediated by a glutathione peroxidase-like enzyme, which we name Gpx3, and an orthologue of the Saccharomyces cerevisiae Yap1 binding protein, Ybp1. In addition, Ybp1 also functions to stabilise Cap1 and this novel function is conserved in S. cerevisiae. C. albicans cells lacking Cap1, Ybp1, or Gpx3, are unable to filament and thus, escape from murine macrophages after phagocytosis, and also display defective virulence in the Galleria mellonella infection model. INNOVATION: Ybp1 is required to promote the stability of fungal AP-1-like transcription factors, and Ybp1 and Gpx3 mediated Cap1-dependent oxidative stress responses are essential for the effective killing of macrophages by C. albicans. CONCLUSION: Activation of Cap1, specifically by H2O2, is a prerequisite for the subsequent filamentation and escape of this fungal pathogen from the macrophage.

Live-cell video microscopy of fungal pathogen phagocytosis.

Phagocytic clearance of fungal pathogens, and microorganisms more generally, may be considered to consist of four distinct stages: (i) migration of phagocytes to the site where pathogens are located; (ii) recognition of pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs); (iii) engulfment of microorganisms bound to the phagocyte cell membrane, and (iv) processing of engulfed cells within maturing phagosomes and digestion of the ingested particle. Studies that assess phagocytosis in its entirety are informative but are limited in that they do not normally break the process down into migration, engulfment and phagosome maturation, which may be affected differentially. Furthermore, such studies assess uptake as a single event, rather than as a continuous dynamic process. We have recently developed advanced live-cell imaging technologies, and have combined these with genetic functional analysis of both pathogen and host cells to create a cross-disciplinary platform for the analysis of innate immune cell function and fungal pathogenesis. These studies have revealed novel aspects of phagocytosis that could only be observed using systematic temporal analysis of the molecular and cellular interactions between human phagocytes and fungal pathogens and infectious microorganisms more generally. For example, we have begun to define the following: (a) the components of the cell surface required for each stage of the process of recognition, engulfment and killing of fungal cells; (b) how surface geometry influences the efficiency of macrophage uptake and killing of yeast and hyphal cells; and how engulfment leads to alteration of the cell cycle and behavior of macrophages. In contrast to single time point snapshots, live-cell video microscopy enables a wide variety of host cells and pathogens to be studied as continuous sequences over lengthy time periods, providing spatial and temporal information on a broad range of dynamic processes, including cell migration, replication and vesicular trafficking. Here we describe in detail how to prepare host and fungal cells, and to conduct the video microscopy experiments. These methods can provide a user-guide for future studies with other phagocytes and microorganisms.

Candida albicans infection inhibits macrophage cell division and proliferation.

The pathogenicity of the opportunistic human fungal pathogen Candida albicans depends on its ability to inhibit effective destruction by host phagocytes. Using live cell video microscopy, we show here for the first time that C. albicans inhibits cell division in macrophages undergoing mitosis. Inhibition of macrophage cell division is dependent on the ability of C. albicans to form hyphae, as it is rarely observed following phagocytosis of UV-killed or morphogenesis-defective mutant Candida. Interestingly, failed cell division following phagocytosis of hyphal C. albicans is surprisingly common, and leads to the formation of large multinuclear macrophages. This raises question as to whether inhibition of macrophage cell division is another virulence attribute of C. albicans or enables host macrophages to contain the pathogen.

Stage specific assessment of Candida albicans phagocytosis by macrophages identifies cell wall composition and morphogenesis as key determinants.

Candida albicans is a major life-threatening human fungal pathogen. Host defence against systemic Candida infection relies mainly on phagocytosis of fungal cells by cells of the innate immune system. In this study, we have employed video microscopy, coupled with sophisticated image analysis tools, to assess the contribution of distinct C. albicans cell wall components and yeast-hypha morphogenesis to specific stages of phagocytosis by macrophages. We show that macrophage migration towards C. albicans was dependent on the glycosylation status of the fungal cell wall, but not cell viability or morphogenic switching from yeast to hyphal forms. This was not a consequence of differences in maximal macrophage track velocity, but stems from a greater percentage of macrophages pursuing glycosylation deficient C. albicans during the first hour of the phagocytosis assay. The rate of engulfment of C. albicans attached to the macrophage surface was significantly delayed for glycosylation and yeast-locked morphogenetic mutant strains, but enhanced for non-viable cells. Hyphal cells were engulfed at a slower rate than yeast cells, especially those with hyphae in excess of 20 µm, but there was no correlation between hyphal length and the rate of engulfment below this threshold. We show that spatial orientation of the hypha and whether hyphal C. albicans attached to the macrophage via the yeast or hyphal end were also important determinants of the rate of engulfment. Breaking down the overall phagocytic process into its individual components revealed novel insights into what determines the speed and effectiveness of C. albicans phagocytosis by macrophages.

Non-lytic expulsion/exocytosis of Candida albicans from macrophages.

Candida albicans is an opportunistic pathogen and is recognised and phagocytosed by macrophages. Using live-cell imaging, non-lytic expulsion/exocytosis of C. albicans from macrophages is demonstrated for the first time. Following complete expulsion, both the phagocyte and pathogen remain intact and viable. Partial engulfment of hyphal C. albicans without macrophage lysis is also demonstrated. These observations underpin the complexity of interactions between C. albicans and innate immune cells.

Pathophysiological importance of antineutrophil antibodies in vasculitis.

PURPOSE OF REVIEW: We endeavour to provide a brief overview of the recent advances in understanding of how antineutrophil cytoplasmic antibodies (ANCAs) contribute to the pathophysiology of vasculitis. RECENT FINDINGS: Substantial progress has been made in our understanding of the immunopathogenesis of ANCA-associated vasculitides. Compelling evidence from in-vitro studies and experimental models in conjunction with clinical trials has confirmed that ANCAs directly contribute to the evolution and progression of the disease process. A new ANCA, directed against human lysosome membrane protein-2 (LAMP-2), has recently been described as a sensitive and specific marker for renal vasculitis and we discuss its potential impact for diagnosis and therapy. Furthermore, high-throughput approaches are starting to identify genetic patterns that may identify patients likely to respond to specific therapy or having a high probability of relapse. SUMMARY: It has become increasingly clear over the last two decades that ANCA IgG is pathogenic in vasculitis. Novel therapies aimed at selected cell populations or blocking specific pathogenic pathways offer hope for more selectively treating this heterogeneous group of patients, while avoiding nonspecific immunosuppression and its adverse effects.

Assessment of apoptotic cell phagocytosis by macrophages.

Cells undergo apoptosis during development, tissue homeostasis, and disease, and are rapidly cleared by both professional and nonprofessional phagocytes. In the whole animal, this process is remarkably efficient and usually goes unnoticed. It is estimated that 2 x 10(11) cells are cleared each day and it has been suggested that detection of apoptotic cells in tissues should lead one to at least question the presence of a local clearance defect. For the last two decades, in vitro phagocytosis assays have played a critical role in identifying the receptors and mechanisms involved in the recognition and ingestion of apoptotic cells. The methodology of phagocytosis assays can be broken down into four separate components: apoptosis induction in target cells, preparation of phagocytes, the interaction assay, and the quantitative assessment of apoptotic cell engulfment. Here, we attempt to provide a detailed description of all the individual components of this complex procedure. To date, this has not been done in its entirety but is vital for the accurate assessment of stimuli that influence the clearance process.

Macrophages: promising targets for the treatment of atherosclerosis.

Atherosclerosis is now recognised as a chronic inflammatory disease occurring within the artery wall and ultimately responsible for myocardial infarction, stroke and peripheral vascular disease. A crucial step in atherogenesis is the infiltration of monocytes into the subendothelial space of large arteries where they differentiate into macrophages and become functionally active. Macrophage accumulation within plaques is a hallmark of all stages of atherosclerosis, indeed recent studies have shown their presence has the potential to act as a non-invasive marker of disease activity and plaque stability. Activated macrophages are major players in all stages of lesion development. They not only accumulate lipids but also express effector molecules that are pro-inflammatory, cytotoxic and chemotactic. Furthermore, they secrete enzymes that degrade extracellular matrix leading to plaque destabilisation and increased risk of rupture. However, macrophages are heterogeneous and when appropriately activated they have the potential to drive tissue remodelling and ultimately vascular repair. Pharmacological modulation of macrophage activities therefore represents an important strategy for the prevention and treatment of atherosclerosis and other inflammatory diseases. The aim of this review is to give a brief overview of our current understanding of macrophage activation, distribution and function within inflamed tissue. This will provide the basis for highlighting already available and future methods to exploit specifically activated macrophages as diagnostic and therapeutic targets for atherosclerosis.

Anti-endothelial antibodies interfere in apoptotic cell clearance and promote thrombosis in patients with antiphospholipid syndrome.

Antiphospholipid syndrome is an important cause of recurrent thrombotic events. The pathogenesis of the thrombosis remains unclear, but it has been suggested that anti-phospholipid Abs, which are laboratory markers for the disease and include species capable of binding to vascular endothelial cells, play an important role. We hypothesized that these anti-endothelial Abs promote thrombosis through interference with clearance of dying cells. We show that healthy endothelial cell monolayers effectively remove apoptotic endothelial cells, but this clearance is markedly inhibited by serum or IgG from patients with antiphospholipid syndrome and anti-endothelial Abs. In addition, patient sera or IgG opsonize apoptotic endothelial cells and cause enhanced Fc-mediated uptake by professional phagocytes. Importantly, the delayed clearance of apoptotic cells by healthy endothelial cells and the enhanced Fc-mediated macrophage uptake each result in procoagulant consequences, as judged by increased thrombin generation. The effects on apoptotic cell clearance were reproduced by a mAb derived from a patient with antiphospholipid syndrome, which binds to endothelial cells and is thrombogenic in experimental models. Taken together, our data support a novel, dual mechanism by which anti-endothelial Abs are prothrombotic in antiphospholipid syndrome by inhibiting removal of procoagulant apoptotic cells and by diverting their clearance to provoke inflammatory and prothrombotic changes in professional phagocytes.

Macrophages and hypoxia in human chronic kidney disease.

Chronic kidney disease is characterized by progressive interstitial fibrosis, reduced blood flow, and tubular atrophy, which present a common pathway of destruction irrespective of the initial underlying pathology. There is comprehensive evidence that the interactions of infiltrating macrophages with resident tissue cells play a critical role in this process. A new study now describes the correlation between macrophages, capillary density, and interstitial scarring and suggests distinct differences in early and advanced renal disease.

Immunological consequences of apoptotic cell phagocytosis.

Cells undergo apoptosis in development, tissue homeostasis, and disease and are subsequently cleared by professional and nonprofessional phagocytes. There is now overwhelming evidence that phagocyte function is profoundly altered following apoptotic cell uptake, with consequences for the ensuing innate and adaptive immune response. Pathogens and tumors exploit the changes in macrophage function following apoptotic cell uptake. Here, we will outline the consequences of apoptotic cell phagocytosis and illustrate how apoptotic cells could be used to manipulate the immune response for therapeutic gain.

Differential regulation of phagosome maturation in macrophages and dendritic cells mediated by Rho GTPases and ezrin-radixin-moesin (ERM) proteins.

Deletion of apoptotic cells from tissues involves their phagocytosis by macrophages, dendritic cells, and tissue cells. Although much attention has been focused on the participating ligands, receptors, and mechanisms of uptake, little is known of the disposition of the ingested cell within the phagosome. Here we show that uptake of apoptotic cells by macrophages or fibroblasts results in rapid phagosome maturation, whereas macrophage phagosomes containing Ig-opsonized target cells mature at a slower rate. The early maturation was shown to depend on activation of Rho acting through Rho kinase on ezrin-radixin-moesin proteins. Blockade of Rho signaling or inhibition of moesin both delayed maturation rates to those seen with opsonized targets. By contrast, phagosome maturation in dendritic cells was slower, similar between apoptotic and opsonized target cells, and unaffected by Rho inhibition. These observations have direct implications for the clearance of dying cells and the roles played by different phagocytes in antigen digestion and presentation.

Multiple facets of macrophages in renal injury.

Macrophage infiltration is a common feature of renal disease and their presence has been synonymous with tissue damage and progressive renal failure. More recently work has focused on the heterogeneity of macrophage activation and in particular their ability to curtail inflammation and restore normal function. This has led to the view that it is macrophage function rather than their number that is important in determining the outcome of inflammatory disease. This review will focus on the pathways that regulate macrophage infiltration and activation and how these could be manipulated to control renal inflammatory disease. In particular, the ability of specific cell surface receptors and intracellular signaling pathways to control macrophage activation and how macrophages can be genetically manipulated to develop properties that favor resolution over ongoing injury.