The secreted malarial protein, Cell-Traversal protein for Ookinetes and Sporozoites (CelTOS), is highly conserved among Plasmodium species, and plays a role in the invasion of mosquito midgut cells... Show moreThe secreted malarial protein, Cell-Traversal protein for Ookinetes and Sporozoites (CelTOS), is highly conserved among Plasmodium species, and plays a role in the invasion of mosquito midgut cells and hepatocytes in the vertebrate host. CelTOS was identified as a potential protective antigen based on a proteomic analysis, which showed that CelTOS stimulated significant effector T cells producing IFN-gamma in peripheral blood mononuclear cells (PBMCs) from radiation attenuated sporozoite-immunized, malaria-naive human subjects. In a rodent malaria model, recombinant full-length CelTOS protein/adjuvant combinations induced sterile protection, and in several studies, functional antibodies were produced that had hepatocyte invasion inhibition and transmission-blocking activities. Despite some encouraging results, vaccine approaches using CelTOS will require improvement before it can be considered as an effective vaccine candidate. Here, we report on the use of mRNA vaccine technology to induce humoral and cell-mediated immune responses using this antigen. Several pfceltos encoding mRNA transcripts were assessed for the impact on protein translation levels in vitro. Protein coding sequences included those to evaluate the effects of signal sequence, N-glycosylation on translation, and of nucleoside substitutions. Using in vitro transfection experiments as a pre-screen, we assessed the quality of the expressed CelTOS target relative to the homogeneity, cellular localization, and durability of expression levels. Optimized mRNA transcripts, which demonstrated highest protein expression levels in vitro were selected for encapsulation in lipid nanoparticles (LNP) and used to immunize mice to assess for both humoral and cellular cytokine responses. Our findings indicate that mRNA transcripts encoding pfceltos while potent for inducing antigen-specific cellular cytokine responses in mice, were less able to mount PfCelTOS-specific antibody responses using a two-dose regimen. An additional booster dose was needed to overcome low seroconversion rates in mice. With respect to antibody fine specificities, N-glycosylation site mutated immunogens yielded lower immune responses, particularly to the N-terminus of the molecule. While it remains unclear the impact on CelTOS antigen as immunogen, this study highlights the need to optimize antigen design for vaccine development. Show less
Skin-penetrating parasites have something in common; they all need to evade the initial immune response in the skin in order to avoid being evicted by their hostile host and establish an infection.... Show moreSkin-penetrating parasites have something in common; they all need to evade the initial immune response in the skin in order to avoid being evicted by their hostile host and establish an infection. To do so, they are equipped with the necessary cunning stratagems. For example, they can act directly on immune cells to alter their function and they can optimize their migration patterns to their hostile environment. This thesis is aimed at unravelling those mechanisms. We study two devastating parasitic diseases: Malaria and Schistosomiasis. Both deadly and debilitating parasitic diseases, with over 200 million (malaria) and over 240 million (schistosomiasis) cases annually; the need for potent vaccines is evident. Whole weakened parasites can be used to vaccinate individuals against parasitic diseases like malaria. However, delivery of these parasites in the skin, as is commonly done in vaccinations, reduces their protectivity. We hypothesize that this reduction is caused by parasite-mediated immune-regulatory mechanisms that are initiated upon their first encounter with immune cells in the skin. We investigated whether skin penetrating parasites exploit these existing mechanisms in human skin in order to enhance their survival. Show less
Controlled human infection (CHI) models are an important research tool. Healthy volunteers are experimentally infected with a pathogen. In malaria research the model has been used for decades. Here... Show moreControlled human infection (CHI) models are an important research tool. Healthy volunteers are experimentally infected with a pathogen. In malaria research the model has been used for decades. Here, the model was used to test new Plasmodium falciparum strains, NF135.C10 an NF166.C8, and compare these with the commonly used strain NF54. In addition, a genetically modified malaria vaccine, PfSPZ-GA1, was tested. Unfortunately only few volunteers were protected against malaria.For schistosomiasis, a controlled human schistosomiasis infection (CoHSI) model was developed and hereafter a dose finding study with single-sex male only cercariae was performed. This study showed that in 80% of volunteers 20 cercariae were effective to induce an infection. Although the use of 30 cercariae resulted in 100% infection rate two out of three volunteers developed Katayama syndrome. These side effects were less after infection with 20 cercariae.At last suggestions were made to further improve the CHI model by the use of historical controls. Although this study design can only be used in CHI’s with well-know outcomes these study will be safer by reducing the cumulative risks as less volunteers can be used for these trials. Show less
Background European travellers to endemic countries are at risk of malaria and may be affected by a different range of co-morbidities than natives of endemic regions. The safety profile, especially... Show moreBackground European travellers to endemic countries are at risk of malaria and may be affected by a different range of co-morbidities than natives of endemic regions. The safety profile, especially cardiac issues, of artenimol (previously dihydroartemisinin)-piperaquine (APQ) Eurartesim(R) during treatment of uncomplicated imported falciparum malaria is not adequately described due to the lack of longitudinal studies in this population. The present study was conducted to partially fill this gap. Methods Participants were recruited through Health Care Provider's safety registry in 15 centres across 6 European countries in the period 2013-2016. Adverse events (AE) were collected, with a special focus on cardiovascular safety by including electrocardiogram QT intervals evaluated after correction with either Bazett's (QTcB) or Fridericia's (QTcF) methods, at baseline and after treatment. QTcB and/or QTcF prolongation were defined by a value > 450 ms for males and children and > 470 ms for females. Results Among 294 participants, 30.3% were women, 13.7% of Caucasian origin, 13.5% were current smoker, 13.6% current alcohol consumer and 42.2% declared at least one illness history. The mean (SD) age and body mass index were 39.8 years old (13.2) and 25.9 kg/m(2) (4.7). Among them, 75 reported a total of 129 AE (27 serious), 46 being suspected to be related to APQ (11 serious) and mostly labelled as due to haematological, gastrointestinal, or infection. Women and Non-African participants had significantly (p < 0.05) more AEs. Among AEs, 21 were due to cardiotoxicity (7.1%), mostly QT prolongation, while 6 were due to neurotoxicity (2.0%), mostly dizziness. Using QTcF correction, QT prolongation was observed in 17/143 participants (11.9%), only 2 of them reporting QTcF > 500 ms (milliseconds) but no clinical symptoms. Using QTcB correction increases of > 60 ms were present in 9 participants (6.3%). A trend towards increased prolongation was observed in those over 65 years of age but only a few subjects were in this group. No new safety signal was reported. The overall efficacy rate was 255/257 (99.2%). Conclusions APQ appears as an effective and well-tolerated drug for treatment of malaria in patients recruited in European countries. AEs and QT prolongation were in the range of those obtained in larger cohorts from endemic countries. Trial registration This study has been registered in EU Post-Authorization Studies Register as EUPAS6942 Show less
Using a variety of anti-malaria tools has resulted in a steady decline of malaria in several endemic countries worldwide. An effective vaccine will be critical to halt malaria or even succeed to... Show moreUsing a variety of anti-malaria tools has resulted in a steady decline of malaria in several endemic countries worldwide. An effective vaccine will be critical to halt malaria or even succeed to final eradication. In that perspective, we studied the potential of whole sporozoite immunization by bites of P. falciparum infected mosquitoes under chemoprophylaxis (CPS). In this thesis we further explored this CPS model and assessed different immunizing doses, type of chemoprophylaxis and immunological determinants of disease and protection. We found a clear dose dependent efficacy, independent of type of chemoprophylaxis, found CD107a and CD8 T cells producing granzyme B related to protective immunity. In the field many genetically different strains circulate and a future vaccine should be able to cover multiple strains. We re-challenged volunteers with a different strain and found modest heterologously protection.We retrospectively assessed the parasitological dynamics and adverse events using a positive qPCR rather than thick smear and found reduced the clinical symptoms of malaria for volunteers after challenge.Successful malaria eradication will be more likely to be achieved with a multi-disciplinary approach. Additionally, sufficient and continuous funds will proof to be of tremendous necessity. Show less
For rodent malaria parasites the availability of a variety transgenic parasite lines expressing different reporter proteins under the control of stage-specific or constitutive promoters have been... Show moreFor rodent malaria parasites the availability of a variety transgenic parasite lines expressing different reporter proteins under the control of stage-specific or constitutive promoters have been of great benefit to studies to reveal parasite gene function and to studies focussed on the evaluation of novel drugs and vaccines. The availability of similar transgenic P. falciparum reporter lines would also help to advance gene-function studies and studies aiming at development of new therapies for P. falciparum parasites. In this thesis, we describe a set of studies performed in P. falciparum to develop novel CRISPR/Cas9 methodologies to improve P. falciparum transgenesis and to create novel transgenic parasites that can be used to analyse host-pathogen interactions and for anti-malarial drug and vaccine research. We describe studies aiming at improving CRISPR/Cas9 genetic modification for introduction of transgenes into the genome of P. falciparum using a ‘neutral’ locus, a disruption of the P230p gene using CRISPR/Cas9 showed that P230p like P230 and P48/45, has a vital role in P. falciparum male fertility and zygote formation and the creation of two chimeric P. falciparum parasites (Pf-PvCSP), where the gene encoding circumsporozoite protein (CSP), was replaced by two csp gene variants (VK210 and VK247) showing that species-specific features of CSP govern full sporozoite development. Show less
A vaccine against Plasmodium falciparum is needed to augment currently available malaria control tools. A handful of parasite antigens are at various stages of pre-clinical and clinical development... Show moreA vaccine against Plasmodium falciparum is needed to augment currently available malaria control tools. A handful of parasite antigens are at various stages of pre-clinical and clinical development. Amongst these is P. falciparum apical membrane antigen 1 (PfAMA1), an antigen expressed by asexual stage parasites and believed to be important for the parasite__s invasion of both red blood cells and liver cells. The immune response to PfAMA1 is mediated mainly by antibodies that prevent parasite invasion of host cells. PfAMA1 however shows allelic polymorphism, with anti-PfAMA1 antibody responses exhibiting strain-specificity. This thesis investigated multi-allele vaccine formulation strategies that would overcome the strain-specificity of antibody responses to PfAMA1. The main findings of this thesis are that i) different PfAMA1 alleles share epitopes to which functional cross-strain antibodies can be induced, ii) a three-allele PfAMA1 formulation yields the greatest proportion of functional cross-strain antibodies, and iii) three PfAMA1 alleles, irrespective of the adjuvant used for formulation and whether they are administrated as a multi-allele formulation or sequentially, induce similar proportions of cross-strain antibodies. Overall, a multi-allele formulation with three in silico-designed PfAMA1 candidates yields antibodies that inhibit several parasites in vitro and warrant their development as a human blood stage vaccine. Show less
May, Linda; Bodegom, David van; Frolich, Marijke; Lieshout, Lisette van; Slagboom, P Eline; Westendorp, Rudi GJ and Kuningas, Maris 2010
Toll-like receptors (TLRs) are involved in the induction of an adequate immune response on infection. We hypothesized that genetic variation in TLR4 and TLR2 genes could influence this response and... Show moreToll-like receptors (TLRs) are involved in the induction of an adequate immune response on infection. We hypothesized that genetic variation in TLR4 and TLR2 genes could influence this response and lead to variability in cytokine production and survival. We tested this hypothesis in 4292 participants who were followed up for all-cause mortality for 6 years and live under adverse environmental conditions in the Upper-East region of Ghana, where malaria is endemic. In 605 participants, tumor necrosis factor-a and interleukin-10 (IL10) production, after stimulation with lipopolysaccharide and zymosan, was measured. In addition, 34 single-nucleotide polymorphisms (SNPs) in TLR4 and 12 SNPs in TLR2 were genotyped and tested for association with cytokine production, malaria infection and mortality. In this comprehensive gene-wide approach, we identified novel SNPs in the TLR4 gene that influence cytokine production. From the analyzed SNPs, rs7860896 associated the strongest with IL10 production (P¼0.0005). None of the SNPs in this study associated with malaria or overall mortality risks. In conclusion, we demonstrate that genetic variation within the TLR4 gene influences cytokine production capacity, but in an endemic area does not influence the susceptibility to malaria infection or mortality. Show less
