Bliss' and Loewe's additive and synergistic effects in Plasmodium falciparum growth inhibition by AMA1-RON2L, RH5, RIPR and CyRPA antibody combinations

• Published in: Scientific reports 2020-07, Vol.10 (1), p.11802-11802, Article 11802
• Main Authors: Azasi, Yvonne, Gallagher, Shannon K., Diouf, Ababacar, Dabbs, Rebecca A., Jin, Jing, Mian, Syed Yusuf, Narum, David L., Long, Carole A., Gaur, Deepak, Draper, Simon J., Fay, Michael P., Miller, Louis H., Miura, Kazutoyo
• Format: Article
• Language: English
• Subjects: 631/326/417; 631/326/590; Antibodies; Antibodies, Protozoan - immunology; Antigens; Antigens, Protozoan - immunology; Apical membrane antigen 1; Clinical trials; Erythrocytes; Erythrocytes - parasitology; Humanities and Social Sciences; Immunization; Immunoglobulin G - immunology; Life Cycle Stages - immunology; Malaria; Malaria Vaccines - immunology; Medical research; multidisciplinary; Plasmodium falciparum; Plasmodium falciparum - growth & development; Plasmodium falciparum - immunology; Protective antigen; Proteins; Protozoan Proteins - immunology; Reticulocyte-binding protein; Science; Science (multidisciplinary); Synergistic effect; Vaccine development; Vaccines; Vector-borne diseases
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-67877-8

Plasmodium invasion of red blood cells involves malaria proteins, such as reticulocyte-binding protein homolog 5 (RH5), RH5 interacting protein (RIPR), cysteine-rich protective antigen (CyRPA), apical membrane antigen 1 (AMA1) and rhoptry neck protein 2 (RON2), all of which are blood-stage malaria vaccine candidates. So far, vaccines containing AMA1 alone have been unsuccessful in clinical trials. However, immunization with AMA1 bound with RON2L (AMA1-RON2L) induces better protection against P. falciparum malaria in Aotus monkeys. We therefore sought to determine whether combinations of RH5, RIPR, CyRPA and AMA1-RON2L antibodies improve their biological activities and sought to develop a robust method for determination of synergy or additivity in antibody combinations. Rabbit antibodies against AMA1-RON2L, RH5, RIPR or CyRPA were tested either alone or in combinations in P. falciparum growth inhibition assay to determine Bliss' and Loewe's additivities. The AMA1-RON2L/RH5 combination consistently demonstrated an additive effect while the CyRPA/RIPR combination showed a modest synergistic effect with Hewlett’s S = 1.07 95 % C I : 1.03 , 1.19 . Additionally, we provide a publicly-available, online tool to aid researchers in analyzing and planning their own synergy experiments. This study supports future blood-stage vaccine development by providing a solid methodology to evaluate additive and/or synergistic (or antagonistic) effect of vaccine-induced antibodies.