Research Themes

Main Research Themes

• Identification and analysis of parasite proteins that are (putative) targets for drugs and vaccines
• Development of a malaria vaccine based on genetically attenuated parasites, read more ....
• Analysis of parasite-host interactions involved in pathology and disease 

Research areas

The Malaria Group uses a rodent malaria parasite ( Plasmodium berghei) as a research model for human malaria infections. Our research interests and areas of expertise are:

• Genetic modification of malaria parasites and post-genomic technologies to identify and validate new drug and vaccine targets
• Genomes of malaria parasites (genome organisation, comparative genomics), RNA metabolism and post-transcriptional control of gene expression
• Generation and analysis of genetically attenuated parasites
• Parasite-host interactions involved in pathology and disease
• Anti-malarial drug testing

The Plasmodium berghei rodent model

A malaria parasite of rodents, Plasmodium berghei, is used as the research model in our laboratory. Rodent malaria parasites are practical model organisms for the experimental study of human malaria. These parasites have proved to be analogous to the malarias of man and other primates in most essential aspects of structure, physiology and life cycle.This model has been developed into a sophisticated and functional system for molecular and cellular studies. It is recognised as a valuable model in view of:

• The high similarity between human malaria parasites and P. berghei (for example genome organisation, the genetic make-up,  vaccine target proteins and the molecular basis of drug-resistance).
• The simple and safe manipulation of the complete lifecycle
• Availibility of in vitro cultures for production and manipulation of the parasites
• Availability of the genome sequence, transcriptome and proteome data and technologies for genetic modification
• Availability of genetically modified mutant parasites including transgenic parasites expressing reporter genes such as GFP and Luciferase
• The availability of rodent hosts with characterised genetic backgrounds including transgenic lines.

P. berghei and genetic modification

The P. berghei-research model has significantly contributed to the introduction and application of advanced molecular techniques in malaria research. A major breakthrough was the development of technologies for the genetic modification of malaria parasites that has been pioneered in Leiden. These technologies open an entirely new range of methods for the investigation of developmental biology of malaria parasites and functional analysis of proteins that are targets for vaccines and new drugs.
In our laboratory a number of mutant and transgenic lines of P. berghei have been generated through targeted disruption of genes and through introduction of reporter genes such as Green Fluorescence Protein and Luciferase. Most of these lines are available on request (see also research model).

P. berghei: genomics and post-genomics research

The increasing availability of genome sequence information of different malaria parasites has revealed the similarity between the genomes of human malaria parasites and rodent malaria parasites. Therefore we can use the knowledge of the genome of the rodent parasite P. berghei in a gene discovery program to discover and characterize new vaccine candidates and drug targets.
Detailed transcriptome analysis of various developmental stages (distinct time-points during asexual and sexual development in blood) of the P. berghei have been conducted using microarray chips. Differential transcription profiles have been generated and are available. Proteome analysis studies have been performed in collaboration with Prof. Matthias Mann (Odense, Denmark) and Dr. Edwin lasonder (Nijmegen, The Netherlands), on uniquely acquired life cycle stages (i.e. separated male and female mature P. berghei gametocytes, purified merozoites of different species of Plasmodium; sporozoites). This analysis has been performed using Liquid Chromatography Tandem Mass Spectrometry (LC-MSMS) and the resulting spectra analysed using the MASCOT algorithm. Proteomes generated from different samples have informed targeted gene disruption studies aimed at looking at function of proteins at different points of parasite development; lists of proteins identified by this analysis  can be found here.

P. berghei: Identification and analysis of targets for vaccines and drugs

The P. berghei research model and the development of methods for genetic modification of P. berghei enables the functional analysis of vaccine candidate antigens and investigation of parameters involved in the effective presentation of these antigens so that protective immune responses may be elicited. Several surface proteins that are seen as major vaccine candidate antigens are under investigation at the gene and protein level in our laboratory. 

P. berghei: Anti-malarial drug testing

The P. berghei research model has been optimised for testing new anti-malarial drugs. It is one of the few malaria models available in which anti-malarial efficacy and stage-specific activity can be directly assessed in vitro and compared with the in vivo activity.

Generation and characterisation of live-attenuated Parasite Vaccines

The generation of an effective (>90% protection) and long lasting vaccine against malaria remains one of the most important goals for both control and eradication of malaria. Currently, no fully effective vaccine against malaria exists. Despite years of effort testing many sub-unit vaccines designed against a variety of antigens expressed at various stages of the parasite life-cycle, success has been limited. The complexity of both the parasites life-cycle and host immune responses to infection have contributed to the slow progress in developing an anti-malaria vaccine. Recently, there has been a renewed interest in vaccination using live but attenuated whole parasites. Initially, this approach used radiation-attenuated sporozoites (RAS) and it was established, experimentally, that it was possible to achieve sterile immunity in both mice and humans. This full protective immunity against a malaria infection was only obtained by immunisation with irradiated sporozoites (the infectious form of the parasite injected by the mosquito) that are able to invade liver cells but then completely blocked in their intra-cellular development.
Recently, a comparable attenuation during liver-stage development has been demonstrated using malaria parasites where specific genes, essential for liver stage development, have been removed. Importantly, immunization with these genetically attenuated sporozoites (GAS) results in immune responses identical to RAS. The promise of vaccination by manipulating the parasite genome offers exciting possibilities to generate parasites that completely arrest during liver stage development, but in such a manner that they then induce optimal immune responses, protecting the host against re-infection.
In our group we are not only generating attenuated and protective sporozoites but we are also investigating the possibilities of generating growth- and virulence-attenuated blood stages parasites as potential bloodstage whole-organism vaccine formulations. We are creating and testing many of these genetically attenuated parasites (GAP) using a variety of molecular, cell-biology, imaging and immunological techniques, both in Leiden and in the labs of our collaborators, and are also translating and testing our findings in the human malaria parasite, P. falciparum.