Background Artemisinin derivatives are the leading class of antimalarial drugs due to their rapid onset of action and rapid clearance of circulating parasites. The parasite clearance (PC) half-life measures the rate of loss of parasites from blood after treatment, and this is currently used to assess antimalarial activity of novel agents and to monitor resistance. However, a number of recent studies have challenged the use of PC to measure drug activity, arguing that many circulating parasites may be non-viable. Methods Plasmodium falciparum infected subjects (n=10) in a malaria volunteer infection study were administered a single dose of artesunate (2 mg/kg). Circulating parasite concentration was assessed by quantitative PCR (qPCR). Parasite viability after artesunate administration was estimated by mathematical modelling of the ex vivo growth of parasites collected from subjects. Results We showed that in artemisinin-sensitive infection, viable parasites declined to <0.1% of baseline within 8 h after artesunate administration, while the total number of circulating parasites measured by qPCR remained unchanged. In artemisinin-resistant infections over the same interval, viable parasites declined to 51.4% (SEM: 4.6%) of baseline. Conclusions These results demonstrate that in vivo drug activity of artesunate is faster than is indicated by the PC half-life.
BackgroundAlthough the use of induced blood stage malaria infection has proven to be a valuable tool for testing the efficacy of vaccines and drugs against Plasmodium falciparum, a limiting factor has been the availability of Good Manufacturing Practice (GMP)—compliant defined P. falciparum strains for in vivo use. The aim of this study was to develop a cost-effective method for the large-scale production of P. falciparum cell banks suitable for use in clinical trials.MethodsGenetically-attenuated parasites (GAP) were produced by targeted deletion of the gene encoding the knob associated histidine rich protein (kahrp) from P. falciparum strain 3D7. A GAP master cell bank (MCB) was manufactured by culturing parasites in an FDA approved single use, closed system sterile plastic bioreactor. All components used to manufacture the MCB were screened to comply with standards appropriate for in vivo use. The cryopreserved MCB was subjected to extensive testing to ensure GMP compliance for a phase 1 investigational product.ResultsTwo hundred vials of the GAP MCB were successfully manufactured. At harvest, the GAP MCB had a parasitaemia of 6.3%, with 96% of parasites at ring stage. Testing confirmed that all release criteria were met (sterility, absence of viral contaminants and endotoxins, parasite viability following cryopreservation, identity and anti-malarial drug sensitivity of parasites).ConclusionLarge-scale in vitro culture of P. falciparum parasites using a wave bioreactor can be achieved under GMP-compliant conditions. This provides a cost-effective methodology for the production of malaria parasites suitable for administration in clinical trials.
Background In the absence of a method to culture Plasmodium vivax, the only way to source parasites is ex vivo. This hampers many aspects of P. vivax research. This study aimed to assess the safety of apheresis, a method for selective removal of specific components of blood as a means of extracting and concentrating P. vivax parasites. Methods An iterative approach was employed across four non-immune healthy human subjects in single subject cohorts. All four subjects were inoculated with ~ 564 blood stage P. vivax (HMP013-Pv) and subjected to apheresis 10 to 11 days later. Blood samples collected during apheresis (haematocrit layers 0.5% to 11%) were tested for the presence and concentration of P. vivax by microscopy, flow cytometry, 18S rDNA qPCR for total parasites, and pvs25 qRT-PCR for female gametocyte transcripts. Safety was determined by monitoring adverse events. Malaria transmission to mosquitoes was assessed by membrane feeding assays. Results There were no serious adverse events and no significant safety concerns. Apheresis concentrated asexual parasites by up to 4.9-fold (range: 0.9–4.9-fold) and gametocytes by up to 1.45-fold (range: 0.38–1.45-fold) compared to pre-apheresis densities. No single haematocrit layer contained > 40% of all the recovered P. vivax asexual parasites. Ex vivo concentration of parasites by Percoll gradient centrifugation of whole blood achieved greater concentration of gametocytes than apheresis. Mosquito transmission was enhanced by up to fivefold in a single apheresis sample compared to pre-apheresis. Conclusion The modest level of parasite concentration suggests that the use of apheresis may not be an ideal method for harvesting P. vivax. Trial Registration Australia New Zealand Clinical Trials Registry (ANZCTR) Trial ID: ACTRN12617001502325 registered on 19th October 2017. https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=373812.
Background In the absence of a method to culture Plasmodium vivax, the only way to source parasites is ex vivo. This hampers many aspects of P. vivax research. This study aimed to assess the safety of apheresis, a method for selective removal of specific components of blood as a means of extracting and concentrating P. vivax parasites. MethodsAn iterative approach was employed across four non-immune healthy human subjects in single subject cohorts. All four subjects were inoculated with ~564 blood stage P. vivax (HMP013-Pv) and subjected to apheresis 10 to 11 days later. Blood samples collected during apheresis (haematocrit layers 0.5% to 11%) were tested for the presence and concentration of P. vivax by microscopy, flow cytometry, 18S rDNA qPCR for total parasites, and pvs25 qRT-PCR for female gametocyte transcripts. Safety was determined by monitoring adverse events. Malaria transmission to mosquitoes was assessed by membrane feeding assays. ResultsThere were no serious adverse events and no significant safety concerns. Apheresis concentrated asexual parasites by up to 4.9-fold (range: 0.9 - 4.9-fold) and gametocytes by up to 1.45-fold (range: 0.38 - 1.45-fold) compared to pre-apheresis densities. No single haematocrit layer contained >40% of all the recovered P. vivax asexual parasites. Ex vivo concentration of parasites by Percoll gradient centrifugation of whole blood achieved greater concentration of gametocytes than apheresis. Mosquito transmission was enhanced by up to 5-fold in a single apheresis sample compared to pre-apheresis. ConclusionThe modest level of parasite concentration suggests that the use of apheresis may not be an ideal method for harvesting P. vivax.
Background In the absence of a method to culture Plasmodium vivax , the only way to source parasites is ex vivo . This hampers many aspects of P. vivax research. We assessed the safety of apheresis, a method for selective removal of specific components of blood as a means of extracting and concentrating P. vivax parasites.Methods An iterative approach was employed across four non-immune healthy human subjects in separate cohorts. All four subjects were inoculated with ~564 blood stage P. vivax parasites (HMP013- Pv ) and subjected to apheresis 10 to 11 days later. Blood samples collected during apheresis were tested for the presence and concentration of P. vivax parasites by microscopy, flow cytometry, 18S rDNA qPCR for total parasites, and pvs2 5 qRT-PCR for female gametocyte transcripts. Safety was determined by monitoring adverse events. Malaria transmission to mosquitoes was assessed by membrane feeding assays.Results There were no serious adverse events and no significant safety concerns. Apheresis concentrated asexual parasites by up to 4.9-fold (range: 0.9 - 4.9-fold) and gametocytes by up to 1.45-fold (range: 0.38 - 1.45-fold) compared to pre-apheresis densities. No single haematocrit layer contained >40% of all the recovered P. vivax asexual parasites. Ex vivo concentration of parasites by percoll gradient centrifugation of whole blood achieved greater concentration of gametocytes than apheresis. Mosquito transmission was enhanced by up to 5-fold in a single apheresis sample compared to pre-apheresis.Conclusion The modest level of parasite concentration suggests that the use of apheresis may not be an ideal method for harvesting P. vivax parasites.Trial Registration Australia New Zealand Clinical Trials Registry (ANZCTR) Trial ID: ACTRN12617001502325 registered on 19th October 2017. https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=373812
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.