Overcoming immunogenic gaps in malaria subunit vaccines by broadening CSP regions targeted

The first approval of malaria vaccines RTS,S/AS01 and R21/Matrix M marked a major milestone. Both vaccines present a portion of the Plasmodium falciparum circumsporozoite protein (PfCSP) containing an immunodominant major repeat region, which may limit breadth to other protective epitopes, limiting efficacy and durability. Using B cell receptor (BCR) knock-in mice, we found that the R21-included PfCSP epitope elicited robust B cell responses to the immunodominant major repeats but not to other highly protective epitopes, the minor repeat and junction. We then defined a minimal peptide capable of eliciting minor repeat-specific B cell responses and generating highly protective antibodies (Abs). We characterized these Abs bioinformatically and structurally to identify protective traits, which informed the design of variant Abs with improved affinity. Finally, we demonstrated that vaccination combining the R21-included PfCSP epitope, the minimal minor repeat peptide, and a junctional region immunogen elicited balanced B cell and Ab responses, enhancing protection in vivo. Broadening responses through immunofocusing may overcome immunogenic gaps in current malaria vaccines.