Sterile protection againstPlasmodium vivaxmalaria by repeated blood stage infection in a non-human primate model
Authors: Obaldía Nicanor , Da Silva Filho Joao Luiz , Núñez Marlon , Glass Katherine A. , Oulton Tate , Achcar Fiona , Wirjanata Grennady , Duraisingh Manoj , Felgner Philip , Tetteh Kevin K.A. , Bozdech Zbynek , Otto Thomas D. , Marti Matthias 
Published: February 2023

The malaria parasitePlasmodium vivaxremains a major global public health challenge, causing major morbidity across tropical and subtropical regions. Several candidate vaccines are in preclinical and clinical trials, however no vaccine againstP. vivaxmalaria is approved for use in humans. Here we assessed whetherP. vivaxstrain-transcendent immunity can be achieved by repeated infection inAotusmonkeys. For this purpose, we repeatedly infected six animals with blood stages of theP. vivaxSalvador 1 (SAL-1) strain until sterile immune, and then challenged with the AMRU-1 strain. Sterile immunity was achieved in 4/4Aotusmonkeys after two homologous infections with the SAL-1 strain, while partial protection against a heterologous AMRU-1 challenge (i.e., delay to infection and reduction in peak parasitemia compared to control) was achieved in 3/3 monkeys. IgG levels based onP. vivaxlysate ELISA and protein microarray increased with repeated infections and correlated with the level of homologous protection. Analysis of parasite transcriptional profiles across inoculation levels provided no evidence of major antigenic switching upon homologous or heterologous challenge. In contrast, we observed significant transcriptional differences in theP. vivaxcore gene repertoire between SAL-1 and AMRU-1. Together with the strain-specific genetic diversity between SAL-1 and AMRU-1 these data suggest that the partial protection upon heterologous challenge is due to molecular differences between strains (at genome and transcriptome level) rather than immune evasion by antigenic switching. Our study demonstrates that sterile immunity againstP. vivaxcan be achieved by repeated homologous blood stage infection inAotusmonkeys, thus providing a benchmark to test the efficacy of candidate blood stageP. vivaxmalaria vaccines.

Author summary

Plasmodium vivax is the most widespread human malaria parasite. Elimination efforts are complicated due to the peculiar biology ofP. vivaxincluding dormant liver forms, cryptic reservoirs in bone marrow and spleen and a large asymptomatic infectious reservoir in affected populations. Currently there is no vaccine against malaria caused byP. vivax. Here we induce sterile immunity by repeatedP. vivaxinfection with the SAL-1 strain in non-human primates. In contrast, heterologous challenge with the AMRU-1 strain only provided partial protection. Antibody levels against a crude antigen and a protein microarray correlated with the level of homologous protection. Parasite transcriptional profiles across inoculation levels failed to show major antigenic switching across SAL-1 infections or upon heterologous challenge, instead suggesting other mechanisms of immune evasion. Our study demonstrates that sterile immunity againstP. vivaxcan be achieved by repeated blood stage infection inAotusmonkeys, thus providing a benchmark to test the efficacy of candidate blood stageP. vivaxmalaria vaccines.