Gabriela Minigo

Parasite-dependent expansion of TNF receptor II-positive regulatory T cells with enhanced suppressive activity in adults with severe malaria.

Severe Plasmodium falciparum malaria is a major cause of global mortality, yet the immunological factors underlying progression to severe disease remain unclear. CD4+CD25+ regulatory T cells (Treg cells) are associated with impaired T cell control of Plasmodium spp infection. We investigated the relationship between Treg cells, parasite biomass, and P. falciparum malaria disease severity in adults living in a malaria-endemic region of Indonesia. CD4+CD25+Foxp3+CD127lo Treg cells were significantly elevated in patients with uncomplicated (UM; n = 17) and severe malaria (SM; n = 16) relative to exposed asymptomatic controls (AC; n = 10). In patients with SM, Treg cell frequency correlated positively with parasitemia (r = 0.79, p = 0.0003) and total parasite biomass (r = 0.87, p<0.001), both major determinants for the development of severe and fatal malaria, and Treg cells were significantly increased in hyperparasitemia. There was a further significant correlation between Treg cell frequency and plasma concentrations of soluble tumor necrosis factor receptor II (TNFRII) in SM. A subset of TNFRII+ Treg cells with high expression of Foxp3 was increased in severe relative to uncomplicated malaria. In vitro, P. falciparum–infected red blood cells dose dependently induced TNFRII+Foxp3hi Treg cells in PBMC from malaria-unexposed donors which showed greater suppressive activity than TNFRII− Treg cells. The selective enrichment of the Treg cell compartment for a maximally suppressive TNFRII+Foxp3hi Treg subset in severe malaria provides a potential link between immune suppression, increased parasite biomass, and malaria disease severity. The findings caution against the induction of TNFRII+Foxp3hi Treg cells when developing effective malaria vaccines.

Heroes or villains? T regulatory cells in malaria infection

Infection with Plasmodium parasites can cause severe disease due to a lack of protective immune responses to clear parasitemia, or to the hosts inability to control excessive inflammation resulting in immunopathology. T regulatory cells (Tregs), key mediators of immune homeostasis, are increased in number and modulate disease in human and murine malaria. Several recent studies provide new insights into the mechanisms and functional consequences of Treg induction by P. falciparum. This review integrates and discusses the findings published on Tregs in human and murine malaria to date, with emphasis on Treg induction (host components, kinetics and parasite-dependence) and their diverse roles (protective or pathological) during infection.

Promising particle-based vaccines in cancer therapy

Immunotherapy and preventative cancer vaccines offer the hope of controlling cancer in humans with few of the undesirable side effects associated with current chemotherapy-based methods. Particulate vaccines are effectively taken up by dendritic cells, inducing both T-cell and antibody responses. Virus-like particles (VLPs) have shown preventive efficacy against cervical cancer. Herein we review a range of leading particle-based vaccine approaches: VLPs, immunostimulating complexes, liposomes, synthetic nanoparticles and microparticles (both biocompatible and biodegradable, such as polylactide-co-glycolides and poly[D,L-lactic-co-glycolic] acid). Immune efficacy, regulatory and safety issues, as well the application of immunotherapeutics to immunosuppressed patients with high levels of Tregs are also discussed. We argue that developmental issues (cost and intellectual property lifespan) and the lack of reliable preclinical animal models, rather than the lack of innovative vaccine approaches, currently present a major obstacle to rapid and effective vaccine development.

Neutrophils with myeloid derived suppressor function deplete arginine and constrain T cell function in septic shock patients

IntroductionImpaired T cell function in sepsis is associated with poor outcome, but the mechanisms are unclear. In cancer, arginase-expressing myeloid derived suppressor cells (MDSCs) deplete arginine, impair T cell receptor CD3 zeta-chain expression and T cell function and are linked to poor clinical outcome, but their role during acute human infectious disease and in particular sepsis remains unknown. Hypoarginemia is prevalent in sepsis. This study aimed to determine whether neutrophils that co-purify with PBMC express arginase, and if arginine depletion constrains T cell CD3 zeta-chain expression and function in human sepsis.MethodsUsing flow cytometry, cell culture, HPLC, arginase activity and mRNA detection, our study examined whether neutrophils, with reduced buoyant density isolated in the Ficoll interface, metabolise L-arginine and suppress T cell proliferation in sepsis. A total of 35 sepsis patients (23 with septic shock) and 12 hospital controls in a tertiary referral hospital in tropical Australia were evaluated.ResultsOnly sepsis patients had interphase neutrophils, neutrophils co-purifying with mononuclear cells (≤1.077 specific gravity). The percentage of interphase neutrophils in sepsis was proportional to sepsis severity and correlated with plasma IL-6 concentrations. Ex vivo, sepsis-derived interphase neutrophils expressed arginase, metabolised culture L-arginine and suppressed T cell proliferation and CD3 zeta-chain expression. In vivo, in septic shock there was a longitudinal inverse association between interphase neutrophil number and CD3 zeta-chain expression. Depletion or inhibition of interphase neutrophils in vitro restored zeta-chain expression and T cell function.ConclusionsFor the first time during an acute human infection, interphase neutrophils that express arginase were found to circulate in sepsis, in proportion to disease severity. These neutrophil-MDSCs impair T cell CD3 zeta-chain expression and T cell function via L-arginine metabolism, and likely contribute to the T cell dysfunction seen in sepsis. Modulation of neutrophil-MDSC or their downstream effects warrant consideration as targets for novel adjunctive therapies in sepsis.

Apoptosis and dysfunction of blood dendritic cells in patients with falciparum and vivax malaria

Acute Plasmodium infections in humans result in dendritic cell dysfunction and apoptosis caused in part by elevated levels of IL-10.

Antibodies to Plasmodium falciparum and Plasmodium vivax Merozoite Surface Protein 5 in Indonesia: Species-Specific and Cross-Reactive Responses

BACKGROUND Merozoite surface protein (MSP) 5 is a candidate antigen for a malaria vaccine. In cross-sectional and longitudinal studies, we measured MSP5 antibody responses in Papuans with acute Plasmodium falciparum malaria, Plasmodium vivax malaria, and mixed P. falciparum and P. vivax malaria and in those with past exposure. METHODS Enzyme-linked immunosorbant assay (ELISA) was used to quantitate antibody responses to P. falciparum MSP5 (PfMSP5) and P. vivax MSP5 (PvMSP5) in 82 subjects with P. falciparum infection, 86 subjects with P. vivax infection, 85 subjects with mixed infection, and 87 asymptomatic individuals. Longitudinal responses through day 28 were tested in 20 persons. Cross-reactivity was tested by competition ELISA. RESULTS PfMSP5 or PvMSP5 immunoglobulin (Ig)Gwas detected in 39%-52% of subjects, and IgM was detected in 44%-72%. IgG responses were distributed equally between IgG3 and IgG1 for PfMSP5 but were predominantly IgG3 for PvMSP5. Although IgG responses were generally specific for PfMSP5 or PvMSP5, cross-species reactivity was found in 7 of 107 dual-positive responders. No significant difference was seen in the magnitude, frequency, or subclass of PfMSP5 or PvMSP5 IgG antibodies between groups. There was no significant association between antibody responses and therapeutic response. CONCLUSION PfMSP5 and PvMSP5 were frequently recognized by short-lived, species-specific antibodies. Although infrequent, the cross-reactive MSP5 antibodies indicate that an appropriately formulated vaccine may elicit and/or enhance cross-species recognition, which may be very useful in areas where both parasites are endemic.

Experimentally induced blood stage malaria infection as a tool for clinical research.

A system for experimentally induced blood stage malaria infection (IBSM) with Plasmodium falciparum by direct intravenous inoculation of infected erythrocytes was developed at the Queensland Institute of Medical Research (QIMR) more than 15 years ago. Since that time, this system has been used in several studies to investigate the protective effect of vaccines, the clearance kinetics of parasites following drug treatment, and to improve understanding of the early events in blood stage infection. In this article, we will review the development of IBSM and the applications for which it is being employed. We will discuss the advantages and disadvantages of IBSM, and finish by describing some exciting new areas of research that have been made possible by this system.

The Essential Role of Lipopolysaccharide-Binding Protein in Protection of Mice Against a Peritoneal Salmonella Infection Involves the Rapid Induction of an Inflammatory Response

Acute and chronic hyperinflammation are of major clinical concern, and many treatment strategies are therefore directed to inactivating parts of the inflammatory system. However, survival depends on responding quickly to pathogen attack, and since the adaptive immune system requires several days to adequately react, we rely initially on a range of innate defenses, many of which operate by activating parts of the inflammatory network. For example, LPS-binding protein (LBP) can transfer the LPS of Gram-negative bacteria to CD14 on the surface of macrophages, and this initiates an inflammatory reaction. However, the importance of this chain of events in infection is unclear. First, the innate system is redundant, and bacteria have many components that may serve as targets for it. Second, LBP can transfer LPS to other acceptors that do not induce inflammation. In this study, we show that innate defense against a lethal peritoneal infection with Salmonella requires a direct proinflammatory involvement of LBP, and that this is a major nonredundant function of LBP in this infection model. This emphasizes that blocking the LBP-initiated inflammatory cascade disables an essential defense pathway. Any anti-inflammatory protection that may be achieved must be balanced against the risks inherent in blinding the innate system to the presence of Gram-negative pathogens.

A Complementary Role for the Tetraspanins CD37 and Tssc6 in Cellular Immunity

The cooperative nature of tetraspanin–tetraspanin interactions in membrane organization suggests functional overlap is likely to be important in tetraspanin biology. Previous functional studies of the tetraspanins CD37 and Tssc6 in the immune system found that both CD37 and Tssc6 regulate T cell proliferative responses in vitro. CD37−/− mice also displayed a hyper-stimulatory dendritic cell phenotype and dysregulated humoral responses. In this study, we characterize “double knockout” mice (CD37−/−Tssc6−/−) generated to investigate functional overlap between these tetraspanins. Strong evidence for a cooperative role for these two proteins was identified in cellular immunity, where both in vitro T cell proliferative responses and dendritic cell stimulation capacity are significantly exaggerated in CD37−/−Tssc6−/− mice when compared with single knockout counterparts. Despite these exaggerated cellular responses in vitro, CD37−/−Tssc6−/− mice are not more susceptible to autoimmune induction. However, in vivo responses to pathogens appear poor in CD37−/−Tssc6−/− mice, which showed a reduced ability to produce influenza-specific T cells and displayed a rapid onset hyper-parasitemia when infected with Plasmodium yoelii. Therefore, in the absence of both CD37 and Tssc6, immune function is further altered when compared with CD37−/− or Tssc6−/− mice, demonstrating a complementary role for these two molecules in cellular immunity.

Mannan-mediated gene delivery for cancer immunotherapy

Recent years have seen a resurgence in interest in the development of efficient non‐viral delivery systems for DNA vaccines and gene therapy. We have previously used oxidized and reduced mannan as carriers for protein delivery to antigen‐presenting cells by targeting the receptors that bind mannose, resulting in efficient induction of cellular responses. In the present study, oxidized mannan and reduced mannan were used as receptor‐mediated gene transfer ligands for cancer immunotherapy. In vivo studies in C57BL/6 mice showed that injection of DNA encoding ovalbumin (OVA) complexed to oxidized or reduced mannan‐poly‐L‐lysine induced CD8 and CD4 T‐cell responses as well as antibody responses leading to protection of mice from OVA+ tumours. Both oxidized and reduced mannan delivery was superior to DNA alone or DNA‐poly‐L‐lysine. These studies demonstrate the potential of oxidized and reduced mannan for efficient receptor‐mediated gene delivery in vivo, particularly as DNA vaccines for cancer immunotherapy.