BackgroundThe ability to undertake controlled human malaria infection (CHMI) studies for preliminary evaluation of malaria vaccine candidates and anti-malaria drug efficacy has been limited by the need for access to sporozoite infected mosquitoes, aseptic, purified, cryopreserved sporozoites or blood-stage malaria parasites derived ex vivo from malaria infected individuals. Three different strategies are described for the manufacture of clinical grade cultured malaria cell banks suitable for use in CHMI studies.MethodsGood Manufacturing Practices (GMP)-grade Plasmodium falciparum NF54, clinically isolated 3D7, and research-grade P. falciparum 7G8 blood-stage malaria parasites were cultured separately in GMP-compliant facilities using screened blood components and then cryopreserved to produce three P. falciparum blood-stage malaria cell banks. These cell banks were evaluated according to specific criteria (parasitaemia, identity, viability, sterility, presence of endotoxin, presence of mycoplasma or other viral agents and in vitro anti-malarial drug sensitivity of the cell bank malaria parasites) to ensure they met the criteria to permit product release according to GMP requirements.ResultsThe P. falciparum NF54, 3D7 and 7G8 cell banks consisted of >78% ring stage parasites with a ring stage parasitaemia of >1.4%. Parasites were viable in vitro following thawing. The cell banks were free from contamination with bacteria, mycoplasma and a broad panel of viruses. The P. falciparum NF54, 3D7 and 7G8 parasites exhibited differential anti-malarial drug susceptibilities. The P. falciparum NF54 and 3D7 parasites were susceptible to all anti-malaria compounds tested, whereas the P. falciparum 7G8 parasites were resistant/had decreased susceptibility to four compounds. Following testing, all defined release criteria were met and the P. falciparum cell banks were deemed suitable for release. Ethical approval has been obtained for administration to human volunteers.ConclusionsThe production of cultured P. falciparum blood-stage malaria cell banks represents a suitable approach for the generation of material suitable for CHMI studies. A key feature of this culture-based approach is the ability to take research-grade material through to a product suitable for administration in clinical trials.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0663-x) contains supplementary material, which is available to authorized users.
The malaria parasite, Plasmodium falciparum, invades the human erythrocyte through a complex interaction with erythrocyte receptors characterized by patterns of resistance to various enzymes. As invasion rates are influenced by blood group polymorphisms, we reasoned that the extremely rare rhesus null (Rh(null)) erythrocytes could be informative in characterizing receptors. The aim was to test whether the complete absence of the Rh complex from the cell membrane impacted on parasite invasion. Enzyme treatment patterns for four P. falciparum isolates were first characterised for normal Rh cells. Two isolates showed an enzyme treatment pattern not hitherto described, with resistance to neuraminidase, trypsin and chymotrypsin. In contrast, all isolates had enhanced invasion rates for the Rh(null) cell for all enzyme treatment regimens. The first finding suggests there is another pathway that P. falciparum can utilise to invade the host. We speculate that the Rh null cell membrane exposes a novel ligand defined as Receptor N.
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