Pre-clinical evaluation of a P. berghei-based whole-sporozoite malaria vaccine candidate

Whole-sporozoite vaccination/immunization induces high levels of protective immunity in both rodent models of malaria and in humans. Recently, we generated a transgenic line of the rodent malaria parasite P. berghei ( Pb ) that expresses the P. falciparum ( Pf ) circumsporozoite protein ( Pf CS), and showed that this parasite line ( Pb Vac) was capable of (1) infecting and developing in human hepatocytes but not in human erythrocytes, and (2) inducing neutralizing antibodies against the human Pf parasite. Here, we analyzed Pb Vac in detail and developed tools necessary for its use in clinical studies. A microbiological contaminant-free Master Cell Bank of Pb Vac parasites was generated through a process of cyclic propagation and clonal expansion in mice and mosquitoes and was genetically characterized. A highly sensitive qRT-PCR-based method was established that enables Pb Vac parasite detection and quantification at low parasite densities in vivo. This method was employed in a biodistribution study in a rabbit model, revealing that the parasite is only present at the site of administration and in the liver up to 48 h post infection and is no longer detectable at any site 10 days after administration. An extensive toxicology investigation carried out in rabbits further showed the absence of Pb Vac-related toxicity. In vivo drug sensitivity assays employing rodent models of infection showed that both the liver and the blood stage forms of Pb Vac were completely eliminated by Malarone ® treatment. Collectively, our pre-clinical safety assessment demonstrates that Pb Vac possesses all characteristics necessary to advance into clinical evaluation. Malaria: Pre-clinical characterization of transgenic malaria vaccine Pb Vac is a transgenic malaria parasite expressing circumsporozoite antigen from the human parasite Plasmodium falciparum . Pb Vac elicits neutralizing P. falciparum antibodies and can infect human hepatocytes but not erythrocytes, suggesting that humans would be non-permissive. Miguel Prudêncio and colleagues at the Institute of Molecular Medicine in Lisbon perform a detailed in vivo analysis and toxicology of Pb Vac. Extensive biodistribution analysis using a highly sensitive qPCR in non-permissive rabbit hosts shows Pb Vac are present at the initial bite site early on with later appearance in the liver, but by day 10 is undetectable. Importantly no Pb Vac could be detected in the blood at any time-point. Pb Vac was well tolerated with no apparent