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Fulltext Author Correction: The Plasmodium falciparum male gametocyte protein P230p, a paralog of P230, is vital for ookinete formation and mosquito transmission

Marin-Mogollon C, van de Vegte-Bolmer M, van Gemert GJ, van Pul FJA, Ramesar J, Othman AS, et al.

Sci Rep, 2019 May 03;9(1):7061.
PMID: 31053746 DOI: 10.1038/s41598-019-43505-y

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.
Fulltext The Plasmodium falciparum male gametocyte protein P230p, a paralog of P230, is vital for ookinete formation and mosquito transmission

Marin-Mogollon C, van de Vegte-Bolmer M, van Gemert GJ, van Pul FJA, Ramesar J, Othman AS, et al.

Sci Rep, 2018 10 08;8(1):14902.
PMID: 30297725 DOI: 10.1038/s41598-018-33236-x

Two members of 6-cysteine (6-cys) protein family, P48/45 and P230, are important for gamete fertility in rodent and human malaria parasites and are leading transmission blocking vaccine antigens. Rodent and human parasites encode a paralog of P230, called P230p. While P230 is expressed in male and female parasites, P230p is expressed only in male gametocytes and gametes. In rodent malaria parasites this protein is dispensable throughout the complete life-cycle; however, its function in P. falciparum is unknown. Using CRISPR/Cas9 methodology we disrupted the gene encoding Pfp230p resulting in P. falciparum mutants (PfΔp230p) lacking P230p expression. The PfΔp230p mutants produced normal numbers of male and female gametocytes, which retained expression of P48/45 and P230. Upon activation male PfΔp230p gametocytes undergo exflagellation and form male gametes. However, male gametes are unable to attach to red blood cells resulting in the absence of characteristic exflagellation centres in vitro. In the absence of P230p, zygote formation as well as oocyst and sporozoite development were strongly reduced (>98%) in mosquitoes. These observations demonstrate that P230p, like P230 and P48/45, has a vital role in P. falciparum male fertility and zygote formation and warrants further investigation as a potential transmission blocking vaccine candidate.
Fulltext Chimeric Plasmodium falciparum parasites expressing Plasmodium vivax circumsporozoite protein fail to produce salivary gland sporozoites

Marin-Mogollon C, van Pul FJA, Miyazaki S, Imai T, Ramesar J, Salman AM, et al.

Malar J, 2018 Aug 09;17(1):288.
PMID: 30092798 DOI: 10.1186/s12936-018-2431-1

BACKGROUND: Rodent malaria parasites where the gene encoding circumsporozoite protein (CSP) has been replaced with csp genes from the human malaria parasites, Plasmodium falciparum or Plasmodium vivax, are used as pre-clinical tools to evaluate CSP vaccines in vivo. These chimeric rodent parasites produce sporozoites in Anopheles stephensi mosquitoes that are capable of infecting rodent and human hepatocytes. The availability of chimeric P. falciparum parasites where the pfcsp gene has been replaced by the pvcsp would open up possibilities to test P. vivax CSP vaccines in small scale clinical trials using controlled human malaria infection studies.
METHODS: Using CRISPR/Cas9 gene editing two chimeric P. falciparum parasites, were generated, where the pfcsp gene has been replaced by either one of the two major pvcsp alleles, VK210 or VK247. In addition, a P. falciparum parasite line that lacks CSP expression was also generated. These parasite lines have been analysed for sporozoite production in An. stephensi mosquitoes.
RESULTS: The two chimeric Pf-PvCSP lines exhibit normal asexual and sexual blood stage development in vitro and produce sporozoite-containing oocysts in An. stephensi mosquitoes. Expression of the corresponding PvCSP was confirmed in oocyst-derived Pf-PvCSP sporozoites. However, most oocysts degenerate before sporozoite formation and sporozoites were not found in either the mosquito haemocoel or salivary glands. Unlike the chimeric Pf-PvCSP parasites, oocysts of P. falciparum parasites lacking CSP expression do not produce sporozoites.
CONCLUSIONS: Chimeric P. falciparum parasites expressing P. vivax circumsporozoite protein fail to produce salivary gland sporozoites. Combined, these studies show that while PvCSP can partially complement the function of PfCSP, species-specific features of CSP govern full sporozoite maturation and development in the two human malaria parasites.
Fulltext Expression of full-length Plasmodium falciparum P48/45 in P. berghei blood stages: A method to express and evaluate vaccine antigens

Othman AS, Lin JW, Franke-Fayard BM, Kroeze H, van Pul FJA, Chevalley-Maurel S, et al.

Mol Biochem Parasitol, 2018 Sep;224:44-49.
PMID: 30053393 DOI: 10.1016/j.molbiopara.2018.07.009

The transmission-blocking vaccine candidate Pfs48/45 from the human malaria parasite Plasmodium falciparum is known to be difficult to express in heterologous systems, either as full-length protein or as correctly folded protein fragments that retain conformational epitopes. In this study we express full-length Pfs48/45 in the rodent parasite P. berghei. Pfs48/45 is expressed as a transgene under control of the strong P. berghei schizont-specific msp1 gene promoter (Pfs48/45@PbMSP1). Pfs48/45@PbMSP1 schizont-infected red blood cells produced full-length Pfs48/45 and the structural integrity of Pfs48/45 was confirmed using a panel of conformation-specific monoclonal antibodies that bind to different Pfs48/45 epitopes. Sera from mice immunized with transgenic Pfs48/45@PbMSP1 schizonts showed strong transmission-reducing activity in mosquitoes infected with P. falciparum using standard membrane feeding. These results demonstrate that transgenic rodent malaria parasites expressing human malaria antigens may be used as means to evaluate immunogenicity and functionality of difficult to express malaria vaccine candidate antigens.
Fulltext A P. falciparum NF54 Reporter Line Expressing mCherry-Luciferase in Gametocytes, Sporozoites, and Liver-Stages

Marin-Mogollon C, Salman AM, Koolen KMJ, Bolscher JM, van Pul FJA, Miyazaki S, et al.

Front Cell Infect Microbiol, 2019;9:96.
PMID: 31058097 DOI: 10.3389/fcimb.2019.00096

Transgenic malaria parasites expressing fluorescent and bioluminescent proteins are valuable tools to interrogate malaria-parasite biology and to evaluate drugs and vaccines. Using CRISPR/Cas9 methodology a transgenic Plasmodium falciparum (Pf) NF54 line was generated that expresses a fusion of mCherry and luciferase genes under the control of the Pf etramp10.3 gene promoter (line [email protected]). Pf etramp10.3 is related to rodent Plasmodium uis4 and the uis4 promoter has been used to drive high transgene expression in rodent parasite sporozoites and liver-stages. We examined transgene expression throughout the complete life cycle and compared this expression to transgenic lines expressing mCherry-luciferase and GFP-luciferase under control of the constitutive gapdh and eef1a promoters. The [email protected] parasites express mCherry in gametocytes, sporozoites, and liver-stages. While no mCherry signal was detected in asexual blood-stage parasites above background levels, luciferase expression was detected in asexual blood-stages, as well as in gametocytes, sporozoites and liver-stages, with the highest levels of reporter expression detected in stage III-V gametocytes and in sporozoites. The expression of mCherry and luciferase in gametocytes and sporozoites makes this transgenic parasite line suitable to use in in vitro assays that examine the effect of transmission blocking inhibitors and to analyse gametocyte and sporozoite biology.
Fulltext Creation and preclinical evaluation of genetically attenuated malaria parasites arresting growth late in the liver

Franke-Fayard B, Marin-Mogollon C, Geurten FJA, Chevalley-Maurel S, Ramesar J, Kroeze H, et al.

NPJ Vaccines, 2022 Nov 04;7(1):139.
PMID: 36333336 DOI: 10.1038/s41541-022-00558-x

Whole-sporozoite (WSp) malaria vaccines induce protective immune responses in animal malaria models and in humans. A recent clinical trial with a WSp vaccine comprising genetically attenuated parasites (GAP) which arrest growth early in the liver (PfSPZ-GA1), showed that GAPs can be safely administered to humans and immunogenicity is comparable to radiation-attenuated PfSPZ Vaccine. GAPs that arrest late in the liver stage (LA-GAP) have potential for increased potency as shown in rodent malaria models. Here we describe the generation of four putative P. falciparum LA-GAPs, generated by CRISPR/Cas9-mediated gene deletion. One out of four gene-deletion mutants produced sporozoites in sufficient numbers for further preclinical evaluation. This mutant, PfΔmei2, lacking the mei2-like RNA gene, showed late liver growth arrest in human liver-chimeric mice with human erythrocytes, absence of unwanted genetic alterations and sensitivity to antimalarial drugs. These features of PfΔmei2 make it a promising vaccine candidate, supporting further clinical evaluation. PfΔmei2 (GA2) has passed regulatory approval for safety and efficacy testing in humans based on the findings reported in this study.