Primate malaria parasites as surrogate models to study invasion-blocking antibodies targeting the Plasmodium vivax reticulocyte binding protein 2b

• Grant number: 24/22944-5
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• Start date: June 01, 2025
• End date: May 31, 2026
• Field of knowledge: Biological Sciences - Parasitology - Protozoology of Parasites
• Principal Investigator: Marcelo Urbano Ferreira
• Grantee: Natália Soares Ferreira
• Supervisor: Manoj Duraisingh
• Host Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: Harvard University, Cambridge, United States
• Associated to the scholarship: 24/02290-0 - Naturally acquired anti-RBP2b antibodies, red bllod cell invasion blockade, and protection from Plasmodium vivax Malaria, BP.PD

Abstract

Malaria caused by Plasmodium vivax, the most common form of the disease in the Americas, continues to be a major public health problem, including in Brazil. In order to develop new strategies for controlling and treating vivax malaria, it is essential to gain a better understanding on red blood cell (RBC) invasion mechanisms used by the parasite. One of the key ligand-receptor interactions involves the reticulocyte-binding protein 2b of P. vivax (PvRBP2b), a member of the reticulocyte binding protein (RBP) family, and the transferrin receptor 1 (TfR1 or CD71) expressed on reticulocytes. Murine anti-PvRBP2b monoclonal antibodies can inhibit the PvRBP2b-TfR1 interaction and partially block reticulocyte invasion by P. vivax. Human anti-PvRBP2b monoclonal antibodies can inhibit receptor binding, but a recent study showed that murine and human anti-PvRBP2b monoclonals may not be able to block RBC invasion ex vivo. These negative results were not associated with the high PvRBP2b polymorphism found in the clinical isolates tested. Studies of P. vivax RBC invasion are challenging due the lack of a continuous in vitro culture, but primate malaria parasites closely related to P. vivax - such as P. knowlesi and P. cynomolgi, which can be maintained in continuous culture - offer an excellent model system for in vitro experiments. The P. cynomolgi homolog of RBP2b has 77% identity, at the amino acid level, with the RBP2B of P. vivax strain Salvador 1 (PVX_094255), and such a high similarity allows us to test wild-type parasites in invasion-blocking assays with antibodies to the P. vivax protein. Although P. knowlesi has no members of the RBP family, this parasite expresses two proteins related to the Reticulocyte Binding Protein-like (RBL) family, the Normocyte Binding Proteins Xa and Xb (NBPXa and NBPXb). The present proposal aims to explore intact (wild-type) and genetically modified P. cynomolgi and P. knowlesi as models to analyze the invasion-inhibitory effect of anti-PvRBP2b antibodies. To this end, we will: (1) replace the rbp2b and nbpx genes of P. cynomolgi and P. knowlesi, respectively, with the 5' region of rbp2b gene of P. vivax, which encodes the TfR1 ligand domain, (2) test whether genetically modified parasites have increased tropism for human reticulocytes, and (3) test whether anti-PvRBP2b antibodies can inhibit RBC invasion by intact and genetically modified P. cynomolgi and by genetically modified P. knowlesi. We will standardize a robust in vitro model system for investigating mechanisms underlying red blood cell invasion by P. vivax that can be further explored in our laboratory back in São Paulo.