Evaluating the Functional Impact of Genetic Diversity on Malaria Vaccine Candidates

ABSTRACT
Malaria caused by Plasmodium falciparum remains one of the leading causes of death globally of both
children and pregnant women. The recent global stall in the reduction of malaria deaths has made the
development of a highly effective vaccine essential. A major challenge to developing an efficacious vaccine
is the extensive diversity of Plasmodium falciparum antigens. While genetic diversity plays a major role in
immune evasion and is a barrier to the development of both natural and vaccine-induced protective immunity,
it has been underprioritized in the evaluation of malaria vaccine candidates. This proposal will use genomic
approaches to credential next generation malaria vaccine candidates. Reverse vaccinology is a method of
identifying potential antigens for a vaccine that starts with the genomic sequence of an organism and uses
that information to identify epitopes and antigens that might make suitable vaccine candidates. Since the
genome sequence of Plasmodium falciparum was published, only four new potential candidate vaccines
have entered clinical development, including PfRh5. The main objective of the proposed study is to use a
reverse-vaccinology approach utilizing parasite genomic data directly from infected patients to identify and
functionally interrogate the importance of diversity in these antigens. For these current and novel candidates,
including PfRh5 and binding partners, we will test the role of genetic diversity on immune neutralization by
creating transgenic parasites by using efficient CRISPR-Cas9 genome editing. These parasite lines will be
used to assess the role of specific variants in immune evasion prior to Phase 2 clinical trials. We will use IgG
from malaria-immune individuals, followed closely in long-term longitudinal cohorts, and IgG from subjects in
vaccine trials to assess the degree of inhibition of replication of malaria parasites by growth inhibition assays,
neutrophil respiratory burst, and opsonophagocytosis of merozoites. This approach requires the cohesion of
genomic sequencing technologies to identify potential candidate antigens and naturally occurring diversity,
well-characterized human longitudinal cohorts to follow evolution of infection and immunity, standardized
assays to serve as in vitro correlates of immunity, structure-based approaches for vaccine design, and strong
ties to both scientists and institutions in endemic countries. Our research team is uniquely positioned to
combine these critical requirements to investigate the implications of parasite diversity on the development
of protective immunity and vaccine efficacy, an essential factor to accelerate malaria vaccine discovery. This
approach fills a critical need in the malaria vaccine development field in that it brings genetic diversity in
candidate antigens to the forefront of vaccine candidate validation and credentialing. This study holds
exceptional promise to discover new vaccine candidate combinations that will provide broadly neutralizing
antibodies for inclusion in a globally effective vaccine, one that circumvents the parasite’s natural strategy to
evade the immune system.

Grant Number: 3R01AI168238-04S1
NIH Institute/Center: NIH
Principal Investigator: Amy Bei