Development of a metabolically active, non-replicating sporozoite vaccine to preventPlasmodium falciparummalaria

Abstract

Immunization of volunteers by the bite of mosquitoes carrying radiation-attenuated Plasmodium falciparum sporozoites protects greater than 90% of such volunteers against malaria, if adequate numbers of immunizing biting sessions and sporozoite-infected mosquitoes are used. Nonetheless, until recently it was considered impossible to develop, license and commercialize a live, whole parasite P. falciparum sporozoite (PfSPZ) vaccine. In 2003 Sanaria scientists reappraised the potential impact of a metabolically active, non-replicating PfSPZ vaccine, and outlined the challenges to producing such a vaccine. Six years later, significant progress has been made in overcoming these challenges. This progress has enabled the manufacture and release of multiple clinical lots of a 1(st) generation metabolically active, non-replicating PfSPZ vaccine, the Sanaria PfSPZ Vaccine, submission of a successful Investigational New Drug application to the US Food and Drug Administration, and initiation of safety, immunogenicity and protective efficacy studies in volunteers in MD, US. Efforts are now focused on how best to achieve submission of a successful Biologics License Application and introduce the vaccine to the primary target population of African children in the shortest possible period of time. This will require implementation of a systematic, efficient clinical development plan. Short term challenges include optimizing the (1) efficiency and scale up of the manufacturing process and quality control assays, (2) dosage regimen and method of administration, (3) potency of the vaccine, and (4) logistics of delivering the vaccine to those who need it most, and finalizing the methods for vaccine stabilization and attenuation. A medium term goal is to design and build a facility for manufacturing highly potent and stable vaccine for pivotal Phase 3 studies and commercial launch.

Quantitative assessment of Plasmodium falciparum sexual development reveals potent transmission-blocking activity by methylene blue

“…Integrase-mediated attB × attP recombination yielded NF54 pfs16 , NF54 pfs48/45 , and NF54 mal8p1. 16 reporter lines, which were confirmed by PCR and subsequently cloned.…”

“…Luciferase signals were measured daily from triplicate wells harvested from the parasite lines NF54 pfs16 , NF54 pfs48/45 , and NF54 mal8p1. 16 . Values were normalized to gametocyte numbers and plotted as a proportion of peak promoter activity (normalized to 1.0; mean ± SEM peak luciferase values were 152,398 ± 1,722, 52,052 ± 897, and 2,081 ± 506 for NF54 pfs16 , NF54 pfs48/45 , and NF54 mal8p1.…”

“…Values were normalized to gametocyte numbers and plotted as a proportion of peak promoter activity (normalized to 1.0; mean ± SEM peak luciferase values were 152,398 ± 1,722, 52,052 ± 897, and 2,081 ± 506 for NF54 pfs16 , NF54 pfs48/45 , and NF54 mal8p1. 16 ). Days of gametocytogenesis are represented on the x axis.…”

“…Prior strategies have used transgenes on episomally replicating plasmids (13,15), where the absence of selection during gametocyte development can lead to the loss of plasmids and signal heterogeneity between parasites. Here, transgene integration was applied to the NF54 strain, which produces highly infectious gametocytes and is being used in human malaria vaccine trials (16). Our integration strategy was designed to eliminate the selectable marker that might otherwise interfere with antimalarial modes of action.…”

Immune Responses and Protection of Aotus Monkeys Immunized with Irradiated Plasmodium vivax Sporozoites

“…Currently, the precise mechanisms and antigenic targets of protection have not been elucidated, reflecting the need to re-establish the radiation attenuated model 42,43 to 1) develop a more extensive understanding of the immune mechanism behind the sterilizing immunity and 2) facilitate the discovery of pre-erythrocytic stages antigens involved in protection that could be developed as vaccine candidates. The former could be achieved by the analysis and comparison of protected and unprotected animals and volunteers using blood transcriptional profiles to discover protection signatures, whereas the latter could be approached by using gene-profiling studies.…”