Evaluation of Precision of thePlasmodium knowlesiGrowth Inhibition Assay forPlasmodium vivaxDuffy-Binding Protein-based Malaria Vaccine Development

Abstract

AbstractRecent data indicate increasing disease burden and importance ofPlasmodium vivax(Pv) malaria. A robust assay will be essential for blood-stagePvvaccine development. Results of thein vitrogrowth inhibition assay (GIA) with transgenicP. knowlesi(Pk) parasites expressing thePvDuffy-binding protein region II (PvDBPII) correlate within vivoprotection in the firstPvDBPII controlled human malaria infection (CHMI) trials, making thePkGIA an ideal selection tool once the precision of the assay is defined. To determine the precision in percentage of inhibition in GIA (%GIA) and in GIA50(antibody concentration that gave 50 %GIA), ten GIAs with transgenicPkparasites were conducted evaluating four different anti-PvDBPII human monoclonal antibodies (mAbs) at different concentrations, and three GIAs were conducted testing eighty anti-PvDBPII human polyclonal antibodies (pAbs) at 10 mg/mL. A significant assay-to-assay variation was observed, and the analysis revealed a standard deviation (SD) of 13.1 in the mAb and 5.94 in the pAb dataset for %GIA, with a LogGIA50SD of 0.299 (for mAbs). Moreover, the ninety-five percent confidence interval (95%CI) for %GIA or GIA50in repeat assays was calculated in this investigation. These results will support the development of future blood-stage malaria vaccines, specifically second generationPvDBPII-based formulations.