A Fc-enhanced NTD-binding non-neutralizing antibody delays virus spread and synergizes with a nAb to protect mice from lethal SARS-CoV-2 infection

Emerging evidence indicates that both neutralizing and Fc-mediated effector functions of antibodies contribute to protection against SARS-CoV-2. It is unclear whether Fc-effector functions alone can protect against SARS-CoV-2. Here, we isolated CV3-13, a non-neutralizing antibody, from a convalescent individual with potent Fc-mediated effector functions. The cryoelectron microscopy structure of CV3-13 in complex with the SARS-CoV-2 spike reveals that the antibody binds from a distinct angle of approach to an N-terminal domain (NTD) epitope that only partially overlaps with the NTD supersite recognized by neutralizing antibodies. CV3-13 does not alter the replication dynamics of SARS-CoV-2 in K18-hACE2 mice, but its Fc-enhanced version significantly delays virus spread, neuroinvasion, and death in prophylactic settings. Interestingly, the combination of Fc-enhanced non-neutralizing CV3-13 with Fc-compromised neutralizing CV3-25 completely protects mice from lethal SARS-CoV-2 infection. Altogether, our data demonstrate that efficient Fc-mediated effector functions can potently contribute to the in vivo efficacy of anti-SARS-CoV-2 antibodies.

Interim estimates of 2014/15 vaccine effectiveness against influenza A(H3N2) from Canada's Sentinel Physician Surveillance Network, January 2015

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Interim estimates of 2013/14 vaccine effectiveness against influenza A(H1N1)pdm09 from Canada s sentinel surveillance network, January 2014

The 2013/14 influenza season to date in Canada has been characterised by predominant (90%) A(H1N1)pdm09 activity. Vaccine effectiveness (VE) was assessed in January 2014 by Canada's sentinel surveillance network using a test-negative case-control design. Interim adjusted-VE against medically-attended laboratory-confirmed influenza A(H1N1)pdm09 infection was 74% (95% CI: 58-83). Relative to vaccine, A(H1N1)pdm09 viruses were antigenically similar and genetically well conserved, with most showing just three mutations across the 50 amino acids comprising antigenic sites of the haemagglutinin protein.

Interim estimates of influenza vaccine effectiveness in 2012/13 from Canada's sentinel surveillance network, January 2013

The 2012/13 influenza season in Canada has been characterised to date by early and moderately severe activity, dominated (90%) by the A(H3N2) subtype. Vaccine effectiveness (VE) was assessed in January 2013 by Canada's sentinel surveillance network using a test-negative case-control design. Interim adjusted-VE against medically attended laboratory-confirmed influenza A(H3N2) infection was 45% (95% CI: 13-66). Influenza A(H3N2) viruses in Canada are similar to the vaccine, based on haemagglutination inhibition; however, antigenic site mutations are described in the haemagglutinin gene.

Recombinant attenuated Toxoplasma gondii expressing the Plasmodium yoelii circumsporozoite protein provides highly effective priming for CD8+ T cell-dependent protective immunity against malaria

The protozoan parasite Toxoplasma gondii elicits strong cell-mediated immunity against itself as well as nonspecific resistance against other pathogens and tumors. For this reason, we asked whether recombinant Toxoplasma could be utilized as an effective vaccine vehicle for inducing immunity against heterologous microbial infections. The circumsporozoite protein (PyCSP) of Plasmodium yoelii was engineered into a T. gondii temperature-sensitive strain (ts-4), a mutant that induces complete protection against virulent Toxoplasma challenge. When administered to mice in a single dose, a recombinant ts-4 (CSC3) that both secretes and expresses surface PyCSP induced strong anti-CSP Ab responses, with an isotype distribution pattern similar to that stimulated by the T. gondii carrier. When challenged with P. yoelii sporozoites during the first month after CSC3 vaccination, these animals displayed substantial levels of nonspecific resistance attributable entirely to the T. gondii carrier. Nevertheless, after the nonspecific protection had waned, high levels (up to 79%) of specific immunity against sporozoite challenge were achieved by boosting the animals with recombinant vaccinia virus expressing PyCSP. These CSC3-primed PyCSP-vaccinia-boosted mice displayed high frequencies of splenic PyCSP-specific IFN-gamma-producing cells, as well as CD8+ T cell-dependent cytolytic activity. In vivo depletion of CD8+ lymphocytes at the time of challenge completely ablated protective immunity in the T. gondii-primed/vaccinia-boosted animals, while neutralization of IFN-gamma or IL-12 caused a partial but significant reduction in resistance. Together these findings establish the efficacy of recombinant attenuated Toxoplasma as a vaccine vehicle for priming CD8+-dependent cell-mediated immunity.

Inducible expression of suicide genes in Leishmania donovani amastigotes

This study tests the feasibility of using the A2 gene regulatory system to create a Leishmania cell line in which attenuation is developmentally regulated when the parasite differentiates from promastigotes to amastigotes. The Leishmania donovani- inducible A2 gene regulatory system was used to differentially express in amastigotes two potential suicide genes: a truncated version of the L. donovani 3'-nucleotidase/nuclease expressed in the cytoplasm and the herpes simplex virus thymidine kinase gene. These genes were inserted between A2 noncoding regulatory sequences for up-regulation of expression in amastigotes. The accumulation of toxic products affected L. donovani cell replication and viability both in vitro and in vivo. The inducible expression of toxic gene products represents a valuable tool for the development of safe and effective vaccines.

A2rel: a constitutively expressed Leishmania gene linked to an amastigote-stage-specific gene

The A2-A2rel gene copies are arranged in tandem arrays on a 850 kb chromosome in Leishmania donovani. Contrary to A2 mRNA which displays amastigote-stage-specific expression, A2rel gene expression is constitutive throughout the L. donovani life cycle. The A2rel sequence was found to be conserved in all Leishmania species tested, while the A2 sequence is specific to L. donovani and L. mexicana. The A2rel full length cDNA is of 2.3 kb and it contains one open reading frame coding for a putative protein of 436 amino acids.

Decreased resistance of TNF receptor p55- and p75-deficient mice to chronic toxoplasmosis despite normal activation of inducible nitric oxide synthase in vivo

The importance of TNF-alpha in host defense to the intracellular parasite, Toxoplasma gondii, was investigated in mice lacking both the p55 and p75 receptors for this cytokine. Upon i.p. infection with the avirulent ME49 strain, knockout mice were capable of limiting acute i.p. infection, but succumbed within 3 to 4 wk to a fulminant necrotizing encephalitis. Receptor-deficient mice harbored higher cyst burdens and exhibited uncontrolled tachyzoite replication in the brain. The lack of TNF receptors did not adversely affect the development of a type 1 IFN-gamma response. In vitro studies with peritoneal macrophages stimulated with IFN-gamma and tachyzoites indicated that under limiting concentrations of IFN-gamma, nitric oxide-mediated toxoplasmastatic activity is TNF-alpha dependent. However, this requirement is overcome by increasing the dose of IFN-gamma. Furthermore, both ex vivo and in vivo studies demonstrated that inducible nitric oxide synthase induction in the peritoneal cavity and brain is unimpaired in receptor-deficient mice. Thus, TNF-dependent immune control of T. gondii expansion in the brain involves an effector function distinct from inducible nitric oxide synthase activation.

In vivo microbial stimulation induces rapid CD40 ligand-independent production of interleukin 12 by dendritic cells and their redistribution to T cell areas

The early induction of interleukin (IL)-12 is a critical event in determining the development of both innate resistance and adaptive immunity to many intracellular pathogens. Previous in vitro studies have suggested that the macrophage (MPhi) is a major source of the initial IL-12 produced upon microbial stimulation and that this response promotes the differentiation of protective T helper cell 1 (Th1) CD4+ lymphocytes from precursors that are primed on antigen-bearing dendritic cells (DC). Here, we demonstrate by immunolocalization experiments and flow cytometric analysis that, contrary to expectation, DC and not MPhi are the initial cells to synthesize IL-12 in the spleens of mice exposed in vivo to an extract of Toxoplasma gondii or to lipopolysaccharide, two well characterized microbial stimulants of the cytokine. Importantly, this production of IL-12 occurs very rapidly and is independent of interferon gamma priming or of signals from T cells, such as CD40 ligand. IL-12 production by splenic DC is accompanied by an increase in number of DCs, as well as a redistribution to the T cell areas and the acquisition of markers characteristic of interdigitating dendritic cells. The capacity of splenic DC but not MPhi to synthesize de novo high levels of IL-12 within hours of exposure to microbial products in vivo, as well as the ability of the same stimuli to induce migration of DC to the T cell areas, argues that DC function simultaneously as both antigen-presenting cells and IL-12 producing accessory cells in the initiation of cell-mediated immunity to intracellular pathogens. This model avoids the need to invoke a three-cell interaction for Th1 differentiation and points to the DC as both a sentinel for innate recognition and the dictator of class selection in the subsequent adaptive response.

Vaccination with DNA encoding the immunodominant LACK parasite antigen confers protective immunity to mice infected with Leishmania major

To determine whether DNA immunization could elicit protective immunity to Leishmania major in susceptible BALB/c mice, cDNA for the cloned Leishmania antigen LACK was inserted into a euykaryotic expression vector downstream to the cytomegalovirus promoter. Susceptible BALB/c mice were then vaccinated subcutaneously with LACK DNA and challenged with L. major promastigotes. We compared the protective efficacy of LACK DNA vaccination with that of recombinant LACK protein in the presence or absence of recombinant interleukin (rIL)-12 protein. Protection induced by LACK DNA was similar to that achieved by LACK protein and rIL-12, but superior to LACK protein without rIL-12. The immunity conferred by LACK DNA was durable insofar as mice challenged 5 wk after vaccination were still protected, and the infection was controlled for at least 20 wk after challenge. In addition, the ability of mice to control infection at sites distant to the site of vaccination suggests that systemic protection was achieved by LACK DNA vaccination. The control of disease progression and parasitic burden in mice vaccinated with LACK DNA was associated with enhancement of antigen-specific interferon-gamma (IFN-gamma) production. Moreover, both the enhancement of IFN-gamma production and the protective immune response induced by LACK DNA vaccination was IL-12 dependent. Unexpectedly, depletion of CD8(+) T cells at the time of vaccination or infection also abolished the protective response induced by LACK DNA vaccination, suggesting a role for CD8(+) T cells in DNA vaccine induced protection to L. major. Thus, DNA immunization may offer an attractive alternative vaccination strategy against intracellular pathogens, as compared with conventional vaccination with antigens combined with adjuvants.

Antibody response against a Leishmania donovani amastigote-stage-specific protein in patients with visceral leishmaniasis

The antibody response against an amastigote-specific protein (A2) from Leishmania donovani was investigated. Sera from patients with trypanosomiasis and various forms of leishmaniasis were screened for anti-A2 antibodies. Sera from patients infected only with L. donovani or Leishmania mexicana specifically recognized the A2 recombinant protein. These results were consistent with karyotype analyses which revealed that the A2 gene is conserved in L. donovani and L. mexicana strains. The potential of this antigen in diagnosis was further explored by screening a series of sera obtained from patients in regions of the Sudan and India where L. donovani is endemic. The prevalence of anti-A2 antibodies was determined by Western blotting for all samples. Enzyme-linked immunosorbent assay (ELISA) and an immunoprecipitation assay were also performed on some of the samples. Anti-A2 antibodies were detected by ELISA in 82 and 60% of the samples from individuals with active visceral leishmaniasis (kala-azar) from the Sudan and India, respectively, while the immunoprecipitation assay detected the antibodies in 92% of the samples from India. These data suggest that the A2 protein may be a useful diagnostic antigen for visceral leishmaniasis.

Perforin-mediated cytolysis plays a limited role in host resistance to Toxoplasma gondii

Resistance of perforin knockout (PKO) mice to infection with Toxoplasma gondii was assessed in models of acute infection and during chronic disease. PKO mice vaccinated with the attenuated mutant, ts-4, displayed severely defective CTL responses against tachyzoite-infected targets. Lysis of the NK target, YAC-1, was also severely impaired in PKO mice following ts-4 vaccination. In contrast, wild-type mice developed high levels of CTL and NK lytic activity after ts-4 vaccination. Despite severely defective lytic activity, vaccinated PKO animals were completely resistant to challenge with the virulent strain RH, which normally causes a lethal acute infection. Resistance was attributable to production of IFN-gamma, which remained unimpaired in the PKO animals. In contrast, when PKO mice were infected with low virulence parasite strain ME49, which progresses to the cyst-forming stage after passage through an acute phase, accelerated mortality was observed beginning at 75 days postinfection. A three- to fourfold increase in brain cyst numbers was also found by day 30 in infected PKO animals. Nevertheless, the PKO strain produced normal levels of IFN-gamma after ME49 infection, ruling out impaired production of the latter cytokine as a cause of increased susceptibility. Together, these results show that perforin-dependent cytolytic function is not required for host resistance to lethal acute infection in preimmunized animals, but that the latter activity contributes to the control of infection during the chronic stage.

Perforin-mediated cytolysis plays a limited role in host resistance to Toxoplasma gondii

Resistance of perforin knockout (PKO) mice to infection with Toxoplasma gondii was assessed in models of acute infection and during chronic disease. PKO mice vaccinated with the attenuated mutant, ts-4, displayed severely defective CTL responses against tachyzoite-infected targets. Lysis of the NK target, YAC-1, was also severely impaired in PKO mice following ts-4 vaccination. In contrast, wild-type mice developed high levels of CTL and NK lytic activity after ts-4 vaccination. Despite severely defective lytic activity, vaccinated PKO animals were completely resistant to challenge with the virulent strain RH, which normally causes a lethal acute infection. Resistance was attributable to production of IFN-gamma, which remained unimpaired in the PKO animals. In contrast, when PKO mice were infected with low virulence parasite strain ME49, which progresses to the cyst-forming stage after passage through an acute phase, accelerated mortality was observed beginning at 75 days postinfection. A three- to fourfold increase in brain cyst numbers was also found by day 30 in infected PKO animals. Nevertheless, the PKO strain produced normal levels of IFN-gamma after ME49 infection, ruling out impaired production of the latter cytokine as a cause of increased susceptibility. Together, these results show that perforin-dependent cytolytic function is not required for host resistance to lethal acute infection in preimmunized animals, but that the latter activity contributes to the control of infection during the chronic stage.

The developmental expression of Leishmania donovani A2 amastigote-specific genes is post-transcriptionally mediated and involves elements located in the 3'-untranslated region

Leishmania donovani is a protozoan parasite that exists as a free-living promastigote in the sandfly insect vector and as an amastigote inside the mammalian host macrophage phagolysosome compartment. The L. donovani A2 genes have been described previously as developmentally expressed in amastigotes but can be induced experimentally in promastigotes by a combination of pH and temperature shifts, conditions that mimic the phagolysosomal compartment of the macrophage cell. Considering the importance of the amastigote stage in human infections, we have examined the molecular basis for amastigote stage-specific gene expression. Our results provide evidence that A2 developmental expression during the promastigote-to-amastigote cytodifferentiation is mediated through differential RNA stability and involves the A2 mRNA 3'-untranslated region. The site of processing in the 3'-untranslated region was a major factor for the accumulation of A2 mRNAs in cells incubated under phagolysosomal conditions. The stability of reporter gene transcripts bearing the A2 3'-untranslated region was increased in cells incubated at low pH, further confirming the importance of pH shift as an inducer for A2 expression. These observations contribute to defining the mechanism of amastigote-specific gene regulation in L. donovani. We also demonstrate the feasibility of using the A2 locus to express heterologous genes differentially in the amastigote form of the L. donovani parasite.

Identification and overexpression of the A2 amastigote-specific protein in Leishmania donovani

Leishmania protozoa must adapt rapidly to widely different environments and thus exist as promastigotes in their sandfly host and as amastigotes in their mammalian host. Promastigote differentiation into amastigotes is accompanied by both morphological and biological changes. The molecular mechanisms regulating the differentiation and survival of the different life cycle stages are poorly understood. We have therefore undertaken to identify and characterize amastigote-specific genes and their corresponding products based on the rationale that such products may be involved in the survival in the mammalian host. Previous studies in our laboratory have revealed that the A2 gene family-derived transcripts are abundant in L. donovani amastigotes but are barely detectable in promastigotes. In the present study, we have raised polyclonal and monoclonal antibodies against a recombinant A2 protein synthesized in Escherichia coli. These antibodies have been used to identify a family of A2 proteins ranging from 45 kDa to about 100 kDa which are specifically detected in L. donovani cells when they are cultured in 37 degrees C, and pH 4.5 (conditions which mimic the macrophage phagolysosome) but not in promastigotes cultured at 26 degrees C and pH 7.4. A2 protein therefore represents a unique amastigote-specific protein marker for L. donovani. It is also demonstrated that it was possible to overexpress the A2 protein specifically in amastigote-like cells using a plasmid construct containing the A2 coding and non-coding sequences. These advances set the foundation for defining the biological function of the A2 protein and other genes when specifically expressed in amastigotes.

The expression of biologically active human p53 in Leishmania cells: a novel eukaryotic system to produce recombinant proteins

We have investigated the use of Leishmania cells as a novel eukaryotic expression system for the production of recombinant protein. These cells are easy to maintain, requiring no CO2 incubator or shaker, and can be grown in standard tissue culture media. Leishmania cells can be readily transfected with plasmid DNA by electroporation and transformants selected with antibiotic resistance. Recent studies have shown that it is possible to express foreign genes in Leishmania for the purpose of understanding the biology of this protozoan cell. In the present study we report the use of this system as a means of producing a biologically functional human p53 protein. The conformation of the p53 protein is critical for its ability to bind specific DNA sequences. It is demonstrated that Leishmania-synthesized human p53 is phosphorylated and can bind specifically to its enhancer DNA sequence. These data demonstrate that Leishmania may represent a simple eukaryotic expression system for the production of biologically active recombinant proteins.

Developmental gene expression in Leishmania donovani: differential cloning and analysis of an amastigote-stage-specific gene

Leishmania protozoans are the causative agents of leishmaniasis, a major parasitic disease in humans. During their life cycle, Leishmania protozoans exist as flagellated promastigotes in the sand fly vector and as nonmotile amastigotes in the mammalian hosts. The promastigote-to-amastigote transformation occurs in the phagolysosomal compartment of the macrophage cell and is a critical step for the establishment of the infection. To study this cytodifferentiation process, we differentially screened an amastigote cDNA library with life cycle stage-specific cDNA probes and isolated seven cDNAs representing amastigote-specific transcripts. Five of these were closely related (A2 series) and recognized, by Northern (RNA) blot analyses, a 3.5-kb transcript in amastigotes and in amastigote-infected macrophages. Expression of the amastigote-specific A2 gene was induced in promastigotes when they were transferred from culture medium at 26 degrees C and pH 7.4 to medium at 37 degrees C and pH 4.5, conditions which mimic the macrophage phagolysosomal environment. A2 genes are clustered in tandem arrays, and a 6-kb fragment corresponding to a unit of the cluster was cloned and partially sequenced. An open reading frame found within the A2-transcribed region potentially encoded a 22-kDa protein containing repetitive sequences. The recombinant A2 protein produced in Escherichia coli cells was specifically recognized by immune serum from a patient with visceral leishmaniasis. The A2 protein repetitive element has strong homology with an S antigen of Plasmodium falciparum, the protozoan parasite responsible for malaria. Both the A2 protein of Leishmania donovani and the S antigen of P. falciparum are stage specific and developmentally expressed in mammalian hosts.

Expression of the 4-chlorobenzoate dehalogenase genes from Pseudomonas sp.-CBS3 in Escherichia coli and identification of the gene translation products

The genes encoding the 4-chlorobenzoate dehalogenase of Pseudomonas sp. strain CBS3 were, in an earlier study, cloned in Escherichia coli DH1 with the cosmid vector pPSA843 and then mobilized to the 4-chlorobenzoate dehalogenase minus strain Pseudomonas putida KT2440. In this paper we report on the expression of 4-chlorobenzoate dehalogenase in these clones and on the polypeptide composition of the active enzyme. The dehalogenase activity in whole cells suspended in 3.2 mM 4-chlorobenzoate (30 degrees C) was determined to be approximately 27 units (micromoles 4-hydroxybenzoate produced per minute) per 100 g of E. coli-pPSA843 cells and approximately 28 units per 100 g of P. putida-pPSA843 cells. Dehalogenase activity in fresh cellular extracts (pH 7.4, 30 degrees C) prepared from the E. coli and P. putida clones was unstable and at least 20-fold lower than that observed with the whole cells. The polypeptide components of the dehalogenase were identified by selective expression of the cloned dehalogenase genes and analysis of the gene translation products. Analysis of dehalogenase activity in omega insertion mutants and deletion mutants circumscribed the dehalogenase genes to a 4.8-kilobase (4.8 kb) stretch of the 9.5-kb DNA fragment. Selective expression of the dehalogenase genes from a cloned 4.8-kb DNA fragment in a maxicell system revealed a 30-kDa polypeptide as one of the components of the dehalogenase system. Selective expression of the dehalogenase genes using the T7 polymerase promoter system revealed the 30-kDa polypeptide and 57- and 16-kDa polypeptide products. Determination of which of the three polypeptides were translated in deletion mutants provided the relative positions of the encoding genes on a single DNA strand and the direction in which they are transcribed.

Ancestry of the 4-chlorobenzoate dehalogenase: analysis of amino acid sequence identities among families of acyl:adenyl ligases, enoyl-CoA hydratases/isomerases, and acyl-CoA thioesterases

We have deduced the nucleotide sequence of the genes encoding the three components of 4-chlorobenzoate (4-CBA) dehalogenase from Pseudomonas sp. CBS-3 and examined the origin of these proteins by homology analysis. Open reading frame 1 (ORF1) encodes a 30-kDa 4-CBA-coenzyme A dehalogenase related to enoyl-coenzyme A hydratases functioning in fatty acid beta-oxidation. ORF2 encodes a 57-kDa protein which activates 4-CBA by acyl adenylation/thioesterification. This 4-CBA:coenzyme A ligase shares significant sequence similarity with a large group of proteins, many of which catalyze similar chemistry in beta-oxidation pathways or in siderophore and antibiotic synthetic pathways. These proteins have in common a short stretch of sequence, (T,S)(S,G)G(T,S)(T,E)G(L,X)PK(G,-), which is particularly highly conserved and which may represent an important new class of "signature" sequence. We were unable to find any proteins homologous in sequence to the 16-kDa 4-hydroxybenzoate-coenzyme A thioesterase encoded by ORF3. Analysis of the chemistry and function of the proteins found to be structurally related to the 4-CBA:coenzyme A ligase and the 4-CBA-coenzyme A dehalogenase supports the proposal that they evolved from a beta-oxidation pathway.

Novel enzymic hydrolytic dehalogenation of a chlorinated aromatic

Microbial enzyme systems may be used in the biodegradation of persistent environmental pollutants. The three polypeptide components of one such system, the 4-chlorobenzoate dehalogenase system, have been isolated, and the chemical steps of the 4-hydroxybenzoate-forming reaction that they catalyze have been identified. The genes contained within a 4.5-kilobase Pseudomonas sp. strain CBS3 chromosomal DNA fragment that encode dehalogenase activity were selectively expressed in transformed Escherichia coli. Oligonucleotide sequencing revealed a stretch of homology between the 57-kilodalton (kD) polypeptide and several magnesium adenosine triphosphate (MgATP)-cleaving enzymes that allowed MgATP and coenzyme A (CoA) to be identified as the dehalogenase cosubstrate and cofactor, respectively. The dehalogenase activity arises from two components, a 4-chlorobenzoate:CoA ligase-dehalogenase (an alpha beta dimer of the 57- and 30-kD polypeptides) and a thioesterase (the 16-kD polypeptide).