Search

Vaccine development for Plasmodium vivax, an important human relapsing malaria, is lagging behind. In the case of the most deadly human malaria P. falciparum, unprecedented high levels of protection have been obtained by immunization with live sporozoites under accompanying chemoprophylaxis, which prevents the onset of blood-stage malaria. Such an approach has not been fully evaluated for relapsing malaria. Here, in the P. cynomolgi-rhesus macaque model for relapsing malaria, we employ the parasites’ natural relapsing phenotype to self-boost the immune response against liver-stage parasites, following a single-shot high-dose live sporozoite vaccination. This approach resulted in sterile protection against homologous sporozoite challenge in three out of four animals in the group that was also exposed for several days to blood stages during primary infection and relapses. One out of four animals in the group that received continuous chemoprophylaxis to abort blood-stage exposure was also protected from sporozoite challenge. Although obtained in a small number of animals as part of a Proof-of-Concept study, these results suggest that limited blood-stage parasite exposure may augment protection in this model. We anticipate our data are a starting point for further research into correlates of protection and extrapolation of the single-shot approach to develop efficacious malaria vaccines against relapsing human malaria.

Highlights • miR-26a and miR-30a knockdowns promote differentiation in Fy-transduced K562 cell lines. • miR-26a and miR-30a knockdowns promote enucleation in Fy-transduced K562 cell lines. • Data denote an interplay in the mode of action of miR-26a and miR-30a in erythropoiesis. • Plasmodium cynomolgi and P. knowlesi invade, albeit inefficiently, Fy-transduced K562 cells., Establishing an in vitro “red blood cell matrix” that would allow uninterrupted access to a stable, homogeneous reticulocyte population would facilitate the establishment of continuous, long-term in vitro Plasmodium vivax blood stage cultures. In this study, we have explored the suitability of the erythroleukemia K562 cell line as a continuous source of such reticulocytes and have investigated regulatory factors behind the terminal differentiation (and enucleation, in particular) of this cell line that can be used to drive the reticulocyte production process. The Duffy blood group antigen receptor (Fy), essential for P. vivax invasion, was stably introduced into K562 cells by lentiviral gene transfer. miRNA-26a-5p and miRNA-30a-5p were downregulated to promote erythroid differentiation and enucleation, resulting in a tenfold increase in the production of reticulocytes after stimulation with an induction cocktail compared with controls. Our results suggest an interplay in the mechanisms of action of miRNA-26a-5p and miRNA-30a-5p, which makes it necessary to downregulate both miRNAs to achieve a stable enucleation rate and Fy receptor expression. In the context of establishing P. vivax-permissive, stable, and reproducible reticulocytes, a higher enucleation rate may be desirable, which may be achieved by the targeting of further regulatory mechanisms in Fy-K562 cells; promoting the shift in hemoglobin production from fetal to adult may also be necessary. Despite the fact that K562 erythroleukemia cell lines are of neoplastic origin, this cell line offers a versatile model system to research the regulatory mechanisms underlying erythropoiesis.

Efforts to eradicate Plasmodium vivax malaria are hampered by the presence of hypnozoites, persisting stages in the liver that can reactivate after prolonged periods of time enabling further transmission and causing renewed disease. Large-scale drug screening is needed to identify compounds with antihypnozoite activity, but current platforms rely on time-consuming high-content fluorescence imaging as read-out, limiting assay throughput. We here report an ultrafast and sensitive dual-luciferase-based method to differentiate hypnozoites from liver stage schizonts using a transgenic P. cynomolgi parasite line that contains Nanoluc driven by the constitutive hsp70 promoter, as well as firefly luciferase driven by the schizont-specific lisp2 promoter. The transgenic parasite line showed similar fitness and drug sensitivity profiles of selected compounds to wild type. We demonstrate robust bioluminescence-based detection of hypnozoites in 96-well and 384-well plate formats, setting the stage for implementation in large scale drug screens.

Multidrug resistance (MDR) proteins belong to the B subfamily of the ATP Binding Cassette (ABC) transporters, which export a wide range of compounds including pharmaceuticals. In this study, we used reverse genetics to study the role of all seven Plasmodium MDR proteins during the life cycle of malaria parasites. Four P. berghei genes (encoding MDR1, 4, 6 and 7) were refractory to deletion, indicating a vital role during blood stage multiplication and validating them as potential targets for antimalarial drugs. Mutants lacking expression of MDR2, MDR3 and MDR5 were generated in both P. berghei and P. falciparum, indicating a dispensable role for blood stage development. Whereas P. berghei mutants lacking MDR3 and MDR5 had a reduced blood stage multiplication in vivo, blood stage growth of P. falciparum mutants in vitro was not significantly different. Oocyst maturation and sporozoite formation in Plasmodium mutants lacking MDR2 or MDR5 was reduced. Sporozoites of these P. berghei mutants were capable of infecting mice and life cycle completion, indicating the absence of vital roles during liver stage development. Our results demonstrate vital and dispensable roles of MDR proteins during blood stages and an important function in sporogony for MDR2 and MDR5 in both Plasmodium species.

Malaria parasites actively remodel the infected red blood cell (irbc) by exporting proteins into the host cell cytoplasm. The human parasite Plasmodium falciparum exports particularly large numbers of proteins, including proteins that establish a vesicular network allowing the trafficking of proteins onto the surface of irbcs that are responsible for tissue sequestration. Like P. falciparum, the rodent parasite P. berghei ANKA sequesters via irbc interactions with the host receptor CD36. We have applied proteomic, genomic, and reverse-genetic approaches to identify P. berghei proteins potentially involved in the transport of proteins to the irbc surface. A comparative proteomics analysis of P. berghei non-sequestering and sequestering parasites was used to determine changes in the irbc membrane associated with sequestration. Subsequent tagging experiments identified 13 proteins (Plasmodium export element (PEXEL)-positive as well as PEXEL-negative) that are exported into the irbc cytoplasm and have distinct localization patterns: a dispersed and/or patchy distribution, a punctate vesicle-like pattern in the cytoplasm, or a distinct location at the irbc membrane. Members of the PEXEL-negative BIR and PEXEL-positive Pb-fam-3 show a dispersed localization in the irbc cytoplasm, but not at the irbc surface. Two of the identified exported proteins are transported to the irbc membrane and were named erythrocyte membrane associated proteins. EMAP1 is a member of the PEXEL-negative Pb-fam-1 family, and EMAP2 is a PEXEL-positive protein encoded by a single copy gene; neither protein plays a direct role in sequestration. Our observations clearly indicate that P. berghei traffics a diverse range of proteins to different cellular locations via mechanisms that are analogous to those employed by P. falciparum. This information can be exploited to generate transgenic humanized rodent P. berghei parasites expressing chimeric P. berghei/P. falciparum proteins on the surface of rodent irbc, thereby opening new avenues for in vivo screening adjunct therapies that block sequestration. Molecular & Cellular Proteomics 12: 10.1074/mcp.M112.021238, 426-448, 2013.

Multidrug resistance (MDR) proteins belong to the B subfamily of the ATP Binding Cassette (ABC) transporters, which export a wide range of compounds including pharmaceuticals. In this study, we used reverse genetics to study the role of all seven Plasmodium MDR proteins during the life cycle of malaria parasites. Four P. berghei genes (encoding MDR1, 4, 6 and 7) were refractory to deletion, indicating a vital role during blood stage multiplication and validating them as potential targets for antimalarial drugs. Mutants lacking expression of MDR2, MDR3 and MDR5 were generated in both P. berghei and P. falciparum, indicating a dispensable role for blood stage development. Whereas P. berghei mutants lacking MDR3 and MDR5 had a reduced blood stage multiplication in vivo, blood stage growth of P. falciparum mutants in vitro was not significantly different. Oocyst maturation and sporozoite formation in Plasmodium mutants lacking MDR2 or MDR5 was reduced. Sporozoites of these P. berghei mutants were capable of infecting mice and life cycle completion, indicating the absence of vital roles during liver stage development. Our results demonstrate vital and dispensable roles of MDR proteins during blood stages and an important function in sporogony for MDR2 and MDR5 in both Plasmodium species.

Contains fulltext : 137134.pdf (Publisher’s version ) (Closed access) The 10 Plasmodium 6-Cys proteins have critical roles throughout parasite development and are targets for antimalaria vaccination strategies. We analyzed the conserved 6-cysteine domain of this family and show that only the last 4 positionally conserved cysteine residues are diagnostic for this domain and identified 4 additional "6-Cys family-related" proteins. Two of these, sequestrin and B9, are critical to Plasmodium liver-stage development. RT-PCR and immunofluorescence assays show that B9 is translationally repressed in sporozoites and is expressed after hepatocyte invasion where it localizes to the parasite plasma membrane. Mutants lacking B9 expression in the rodent malaria parasites P. berghei and P. yoelii and the human parasite P. falciparum developmentally arrest in hepatocytes. P. berghei mutants arrest in the livers of BALB/c (100%) and C57BL6 mice (>99.9%), and in cultures of Huh7 human-hepatoma cell line. Similarly, P. falciparum mutants while fully infectious to primary human hepatocytes abort development 3 d after infection. This growth arrest is associated with a compromised parasitophorous vacuole membrane a phenotype similar to, but distinct from, mutants lacking the 6-Cys sporozoite proteins P52 and P36. Our results show that 6-Cys proteins have critical but distinct roles in establishment and maintenance of a parasitophorous vacuole and subsequent liver-stage development.

We describe a technology for imaging the sequestration of infected red blood cells (iRBC) of the rodent malaria parasite Plasmodium berghei both in the bodies of live mice and in dissected organs, using a transgenic parasite that expresses luciferase. Real-time imaging of sequestered iRBC is performed by measuring bioluminescence produced by the enzymatic reaction in parasites between the luciferase enzyme and its substrate luciferin injected into the mice several minutes prior to imaging. The bioluminescence signal is detected by a sensitive I-CCD photon-counting video camera. Using a reporter parasite that expresses luciferase under the control of a schizont-specific promoter (i.e., the ama-1 promoter), the schizont stage is made visible when detecting bioluminescence signals. Schizont sequestration is imaged during short-term infections with parasites that are synchronized in development or during ongoing infections. Real-time in vivo imaging of iRBC will provide increased insights into the dynamics of sequestration and its role in pathology, and can be used to evaluate strategies that prevent sequestration.

Research on the biology of malaria parasites has greatly benefited from the application of reverse genetic technologies, in particular through the analysis of gene deletion mutants and studies on transgenic parasites that express heterologous or mutated proteins. However, transfection in Plasmodium is limited by the paucity of drug-selectable markers that hampers subsequent genetic modification of the same mutant. We report the development of a novel ‘gene insertion/marker out’ (GIMO) method for two rodent malaria parasites, which uses negative selection to rapidly generate transgenic mutants ready for subsequent modifications. We have created reference mother lines for both P. berghei ANKA and P. yoelii 17XNL that serve as recipient parasites for GIMO-transfection. Compared to existing protocols GIMO-transfection greatly simplifies and speeds up the generation of mutants expressing heterologous proteins, free of drug-resistance genes, and requires far fewer laboratory animals. In addition we demonstrate that GIMO-transfection is also a simple and fast method for genetic complementation of mutants with a gene deletion or mutation. The implementation of GIMO-transfection procedures should greatly enhance Plasmodium reverse-genetic research.

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Authors’ original file for figure 4

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file 5: List of primers used in this study. Left column: primer number. Middle column: Primer sequence. Right column: Description of primer and orientation (F: Forward, R: Reverse). (PDF 63 KB)

Authors’ original file for figure 3

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Authors’ original file for figure 4

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Authors’ original file for figure 3

Additional file 5: List of primers used in this study. Left column: primer number. Middle column: Primer sequence. Right column: Description of primer and orientation (F: Forward, R: Reverse). (PDF 63 KB)

Authors’ original file for figure 2

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Authors’ original file for figure 1

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file 4: Location of intron within the 5'ITR of piggyBac. Green letters: gfp CDS. Black underlined letters: piggyBac 5' ITR. Black underlined bold letters: Intron. (PDF 17 KB)

Additional file 6: TAIL PCR conditions during Primary, Secondary and Tertiary rounds of PCR (adapted from [75]). (PDF 29 KB)

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file 4: Location of intron within the 5'ITR of piggyBac. Green letters: gfp CDS. Black underlined letters: piggyBac 5' ITR. Black underlined bold letters: Intron. (PDF 17 KB)

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Authors’ original file for figure 1

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file 3: Generation of parasites lacking expression of P41 (Δ p41 ) or Metacaspase2 (Δ metacaspase2 ). (A) Schematic representation of the construct used for disruption of p41 and metacaspase2. Correct integration of the construct results in disruption of the genes as shown (replacement locus) and was analysed by Southern analysis of PFG-separated chromosomes and diagnostic PCR (see B and C). See (Additional file 5 Table S3) for primer details. Black boxes: target regions; grey box: tgdhfr-ts selectable marker cassette. (B) PCR analysis of correct disruption of p41, Northern analysis of transcription in wild type (wt) and mutant (318cl1) and Southern analysis of PFG-separated chromosomes. PCRs were performed with primers that amplify the 5' (INT1 and L313) region of the disrupted locus (5' int) or the intact ORF (INT1, INT2), c: Control PCR amplifying the p28 gene. Chromosomes were hybridized with the 3'-dhfr probe recognizing the p41-construct integrated in chromosome 10 and the endogenous dhfr-ts gene on chromosome 7. TM4 is a probe recognizing rRNA and used as a loading control. (C) PCR analysis of correct disruption of the metacaspase2 and Southern analysis of PFG-separated chromosomes in wild type (wt) and mutant (796cl1) (right-hand panel). PCRs were performed with primers that amplify the 5' (INT1 and 313) region of the disrupted locus (5' int) or the intact ORF (INT1, INT2), c: Control PCR amplifying the p28 gene. Chromosomes were hybridized with the 3'-dhfr probe recognizing the metacaspase2 construct integrated in chromosome 10, the endogenous dhfr-ts gene on chromosome 7 and the integrated GFP-construct in chromosome 3 of the parent line 507cl1. (PDF 147 KB)

Additional file of Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

Additional file 3: Generation of parasites lacking expression of P41 (Δ p41 ) or Metacaspase2 (Δ metacaspase2 ). (A) Schematic representation of the construct used for disruption of p41 and metacaspase2. Correct integration of the construct results in disruption of the genes as shown (replacement locus) and was analysed by Southern analysis of PFG-separated chromosomes and diagnostic PCR (see B and C). See (Additional file 5 Table S3) for primer details. Black boxes: target regions; grey box: tgdhfr-ts selectable marker cassette. (B) PCR analysis of correct disruption of p41, Northern analysis of transcription in wild type (wt) and mutant (318cl1) and Southern analysis of PFG-separated chromosomes. PCRs were performed with primers that amplify the 5' (INT1 and L313) region of the disrupted locus (5' int) or the intact ORF (INT1, INT2), c: Control PCR amplifying the p28 gene. Chromosomes were hybridized with the 3'-dhfr probe recognizing the p41-construct integrated in chromosome 10 and the endogenous dhfr-ts gene on chromosome 7. TM4 is a probe recognizing rRNA and used as a loading control. (C) PCR analysis of correct disruption of the metacaspase2 and Southern analysis of PFG-separated chromosomes in wild type (wt) and mutant (796cl1) (right-hand panel). PCRs were performed with primers that amplify the 5' (INT1 and 313) region of the disrupted locus (5' int) or the intact ORF (INT1, INT2), c: Control PCR amplifying the p28 gene. Chromosomes were hybridized with the 3'-dhfr probe recognizing the metacaspase2 construct integrated in chromosome 10, the endogenous dhfr-ts gene on chromosome 7 and the integrated GFP-construct in chromosome 3 of the parent line 507cl1. (PDF 147 KB)

Authors’ original file for figure 2