Extent, dynamics and mechanisms of Plasmodium vivax immune evasion caused by PvDBP gene amplification

Elimination of Plasmodium vivax (Pv) malaria parasites would greatly benefit from a blood-stage vaccine. PvDBP is a parasite ligand involved in erythrocyte invasion through the interaction with its human receptor, the Duffy protein. This interaction is critical for the parasite’s entry making PvDBP the most advanced candidate for a blood-stage vaccine with Phase II clinical trials undergoing. Recent work has identified and characterized human monoclonal antibodies (humabs) that allow strain-transcending neutralization of parasites regardless of their PvDBP sequence diversity. However, it has been demonstrated that Pv collected in Cambodia with multiple copies of the PvDBP gene were able to overcome in vitro neutralization by these humabs. These observations provided the first evidence for an evolutionary advantage for pvdbp amplification, widespread in Pv populations, and created a new paradigm in which to consider pathogen immune evasion mechanisms. These results raise the concern that implementation of a PvDBP vaccine may select for multi-pvdbp copy parasites. By evaluating the in vitro neutralization by anti-PvDBP humabs of single and multi-pvdbp copy parasites from Ethiopia, it will enable the evaluation of the extent of the immune evasion phenotype conferred by pvdbp amplification described with Cambodian Pv.  By (i) associating in vitro invasion rates with the full-length Duffy sequences of invaded erythrocytes, and (ii) prospectively testing for association between pvdbp copy number and human Duffy sequences in participants enrolled in longitudinal cohorts in Cambodia and in Ethiopia, it will be enable the determination of the relation between pvdbp amplification and Duffy human polymorphism. Through the analysis of the serological dynamics of the longitudinal cohorts’ participants, the measure of Pv infections and the pvdbp copy number of infecting parasites, it will help to test if the gene amplification is selected in vivo by the immune status of human hosts and how it correlates with changes in Pv prevalence in the population. In vitro experimental evolution of Pk lines will provide complementary evidence for selection of pvdbp amplification by anti-PvDBP humabs. The project will specifically test if immune evasion results from increased protein quantity produced by multi-copy parasites and/or from epitope variations through multiple, different alleles and variants present simultaneously in a given parasite. Through a combination of phenotyping and genomic approaches, the results will provide invaluable data to inform on strategies to overcome this immune evasion in the context of vaccine development. .

NIH Project details

P. vivax
Vaccines (Immune Correlates)

Jul 2023 — Jun 2028

$626,201

Cambodia
Ethiopia

Towards a vaccine for Plasmodium vivax