Identification of Novel Malaria Antigens Expressed on the Surface of RBCs Infected with Plasmodium falciparum

Background/Objectives: Malaria affects almost half of the world’s population and causes more than 600,000 deaths annually. Young children in malaria-endemic areas have the highest mortality rate because of their immature immune systems. Global efforts to control the disease have had limited success, with two WHO-recommended pre-erythrocytic malaria vaccines showing suboptimal efficacy; no vaccine has yet been approved against the blood stages of the parasite that causes the clinical symptoms of malaria. Therefore, there is an urgent need to identify new vaccine candidates against the parasite’s blood stages to achieve protection against the disease. Methods: Previous studies in our lab identified a few potential vaccine candidates expressed on the surface of malaria-parasite-infected RBCs using sera from disease-resistant children from malaria-endemic regions and a phage-displayed cDNA library generated from P. falciparum. In an innovative approach, we successfully immunized mice using live Plasmodium falciparum-infected red blood cells {Pf-iRBCs (L)}, the membrane fraction of P. falciparum-infected RBCs {Pf-iRBCs (M)}, and live uninfected human red blood cells (hRBCs) in suitable adjuvants. The polyclonal sera produced against Pf-iRBC immunizations were evaluated for specificity and parasite inhibition in vitro and used in a phage display biopanning assay to identify novel antigens on the surface of Pf-iRBCs. Results: Our data indicate that the polyclonal serum produced in BALB/cJ mice, against live Pf-iRBC (L) and their membrane fraction, specifically interacts with surface antigens of parasitic origin on Pf-iRBCs. Additionally, the anti-Pf-iRBC polyclonal serum exhibits significant parasite-killing activity in the in vitro growth inhibition assay (GIA). We have identified both known and novel antigens associated with the Pf-iRBC membrane using phage display cDNA library screening assays. Conclusions: As a proof of concept, our phage display screening identified antigens known to be associated with the Pf-iRBC membrane. Additionally, we identified several unknown Pf-iRBC antigens predicted to be associated with Pf-iRBC membrane (PlasmoDB), suggesting that our approach has the potential to identify novel antigens yet to be evaluated as vaccine candidates against falciparum malaria. In our follow-on studies, we will evaluate the newly identified antigen using an integrated in vitro and in vivo challenge experiment. These studies form the core supporting data for further evaluation of the vaccine potential of novel Pf-iRBC antigens and for follow-on vaccine trials in non-human primates, with an ultimate goal of a malaria vaccine for humans.