PfCSP-ferritin nanoparticle malaria vaccine antigen formulated with aluminum-salt and CpG 1018® adjuvants: Preformulation characterization, antigen-adjuvant interactions, and mouse immunogenicity studies

Circumsporozite protein (CSP), the most abundant surface protein in parasitic <i>Plasmodium falciparum</i> (Pf) sporozoite and an attractive target for malaria vaccine design, has been shown to induce protective humoral response in humans. In this work, we characterized and formulated a promising recombinant PfCSP immunogen (155) candidate consisting of two PfCSP epitopes (i.e. junction, NANP repeat) fused to <i>H. pylori</i> apoferritin forming a 24-mer nanoparticle. In addition, two N-linked glycans were engineered to mitigate possible anti-apoferritin immune responses, and a universal T-cell epitope was included to further enhance immunogenicity. Physicochemical characterization of the 155 antigen was performed including primary structure, post-translational modifications, conformational stability, and particle size. A competitive ELISA was developed to assess antigen binding to a PfCSP-specific mAb. The <i>in vitro</i> antigenicity of the 155 antigen was measured upon formulation with adjuvants, including aluminum-salts (i.e. Alhydrogel^TM, Adju-Phos^TM) and the TLR-9 agonist CpG 1018®, when freshly combined and after storage at different temperatures over 3 months. The <i>in vivo</i> immunological impact of various adjuvanted formulations of the 155 antigen was investigated in mice. The results support the formulation of 155 with Alhydrogel^TM + CpG 1018® adjuvants as a promising recombinant malaria vaccine candidate from both a pharmaceutical and immunological perspective.