Rapid Fire Presentation 8th International Conference on Plasmodium vivax Research 2022

Evaluating the primate malaria parasites P. cynomolgi and P. knowlesi as in vitro models for understanding P. vivax invasion and vaccinology (#209)

Sheena Dass 1 , Prasun Kundu 2 , Deboki Naskar 2 , Usheer Kanjee 1 , Anaclara Pincelli 3 , Marcelo U Ferreira 3 , Julian C Rayner 2 , Manoj T Duraisingh 1
  1. Harvard T.H. Chan School of Public Health, Boston, Massachusetts, United States
  2. Cambridge Institute of Medical Research, Cambridge University, Cambridge, United Kingdom
  3. University of São Paolo, São Paolo, Brazil

Plasmodium vivax initiates its intra-erythrocytic developmental cycle with a multistep invasion process involving interactions between numerous parasite ligands and red blood cell host receptors. Owing in part to its preference for invading reticulocytes, there is no long-term in vitro culture system for P. vivax, which limits efforts to identify high-priority targets for blood stage vaccine development. Here we aim to evaluate the conservation in antigenicity of P. vivax invasion ligand proteins with related simian malaria parasite species P. cynomolgi and P. knowlesi. A panel of 8 P. vivax proteins (DBP, TRAg17, TRAg21, MSP8, GAMA, P12p, P41p and PVP01_1207200) were selected because of their putative roles in erythrocyte invasion, and conservation of shared functional domains albeit varying homology(50-89%), pronounced with P. cynomolgi versus P. knowlesi. Full-length ectodomains of all eight P. vivax proteins were expressed recombinantly in the HEK293E system and purified protein used to generate polyclonal antibodies. Immunofluorescence assays were conducted to screen these antibodies, demonstrating their ability to recognize corresponding parasite ligands in all three sister species. To determine the invasion inhibitory strength of these antibodies we developed a robust 384-well based miniature scale assay allowing the use of lower levels of hematocrit, parasite inoculum and antibody volumes. We generated dose-response curves and IC50 values for all 8 antibodies against P. cynomolgi and P. knowlesi, demonstrating comparable levels of inhibition in both species, and identifying some novel candidates with high invasion inhibitory activity. Experiments with Brazilian P. vivax isolates are ongoing to measure the inhibitory effects of the antibodies against P. vivax, thereby allowing the first direct quantitative comparison between the three species. Overall, this study aims to propose alternate efficient and robust model systems employing simian malaria parasite species, ultimately facilitating the prioritization of P. vivax-targeted blood stage vaccine candidates