Defining targets of protective immunity in Plasmodium vivax using human monoclonal antibodies

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Plasmodium vivax (Pv) is a major cause of malaria worldwide and frequently results in illness among active duty military personnel. It is also an important cause of malaria in veterans because the parasite develops a latent stage of infection that can relapse years later. Our aim is to develop a vaccine and novel therapeutics for Pv. The goal for vaccine development efforts is a multi-component vaccine that targets multiple stages of the Pv life cycle in humans. In this proposal, our focus is on two essential Pv proteins required for parasitic invasion of red blood cells (in this case, reticulocytes). These are the Duffy Binding Protein (DBP) and the Reticulocyte Binding Protein 2b (RBP2b). Our approach is to generate human monoclonal antibodies (mAbs) from individuals with naturally-acquired immunity to Pv. Using B cells from donors with robust immune responses, we will identify B cells specific for DBP and RBP2b and generate mAbs against these two essential invasion proteins. We will test whether the mAbs can block the binding of Pv proteins to their receptors on reticulocytes and if so, whether they can inhibit Pv invasion of reticulocytes in vitro. We will then determine which Pv protein targets (epitopes) are recognized by the most effective mAbs. We will identify the mAb targets that are likely to be present in Pv strains globally and thus useful for inclusion in a pan-global vaccine. The most promising mAbs will then be tested for their ability to protect against Pv blood stage infection in an Aotus monkey model of Pv infection. Working with our collaborators at the NAMRU-6 primate unit in Peru, mAbs will be passively transferred to Aotus monkeys and the animals monitored for protection against Pv malaria. Pending the outcome of our animal protection experiments, we will proceed with further development of a vaccine candidate (an immunogen) that incorporates the essential Pv targets identified. We will use a novel animal-based approach to generate stable immunogens known as nanobodies or VHH antibodies. Our studies will involve a carefully orchestrated collaboration by experienced scientists working on malaria at the Veterans Affairs Medical Center in Cleveland, OH; Center for Global Health and Diseases at Case Western Reserve University in Cleveland, OH; Malaria Unit, Institute Pasteur, Cambodia; Walter and Eliza Hall Institute, Australia; and the NAMRU-6 unit in Peru. Our results will enable progress toward a multi-component vaccine against Pv. They will also advance the potential of antibody therapies for severely ill individuals and those in need of sustained prophylaxis during seasonal transmission and tours of duty. !