Design of Alphavirus Virus-Like Particles Presenting Circumsporozoite Junctional Epitopes That Elicit Protection against Malaria

Abstract

The most advanced malaria vaccine, RTS,S, includes the central repeat and C-terminal domains of the Plasmodium falciparum circumsporozoite protein (PfCSP). We have recently isolated human antibodies that target the junctional region between the N-terminal and repeat domains that are not included in RTS,S. Due to the fact that these antibodies protect against malaria challenge in mice, their epitopes could be effective vaccine targets. Here, we developed immunogens displaying PfCSP junctional epitopes by genetic fusion to either the N-terminus or B domain loop of the E2 protein from chikungunya (CHIK) alphavirus and produced CHIK virus-like particles (CHIK-VLPs). The structural integrity of these junctional-epitope–CHIK-VLP immunogens was confirmed by negative-stain electron microscopy. Immunization of these CHIK-VLP immunogens reduced parasite liver load by up to 95% in a mouse model of malaria infection and elicited better protection than when displayed on keyhole limpet hemocyanin, a commonly used immunogenic carrier. Protection correlated with PfCSP serum titer. Of note, different junctional sequences elicited qualitatively different reactivities to overlapping PfCSP peptides. Overall, these results show that the junctional epitopes of PfCSP can induce protective responses when displayed on CHIK-VLP immunogens and provide a basis for the development of a next generation malaria vaccine to expand the breadth of anti-PfCSP immunity.

Vaccination in a humanized mouse model elicits highly protective PfCSP-targeting anti-malarial antibodies

“…To address this, we produced a prototypical immunogen using an approach from the field of HIV-1 vaccine research (Xu et al, 2018) and found that a junctional epitope-focused immunization strategy induced a strong response from H iGL-CIS43 k iGL-CIS43 B cells. This is in agreement with two recent studies showing that the junctional epitope, when displayed on an alphavirus viruslike particle (VLP) (Francica et al, 2021) or Qb bacteriophage VLPs (Jelı ´nkova ´et al, 2021), elicits partial protection against (B) Crystal structures of junctional peptide (peptide 21) in complex with the most potent iGL-CIS43-derived antibodies from m42 and m43, highlighting similarity in SHM (left) and variation in bound epitope, especially in relationship to isoleucine or leucine at HC position 98 (right). Numbering on peptide 21 corresponds to the PfCSP numbering.…”

The light chain of the L9 antibody is critical for binding circumsporozoite protein minor repeats and preventing malaria

“…However, the isolation of rare and potent mAbs that preferentially bind NPDP (Kisalu et al, 2018;Tan et al, 2018) or the NVDP repeats (Wang et al, 2020) identified these subdominant epitopes as sites of vulnerability on PfCSP. As these epitopes are not contained in RTS,S, these discoveries led to the development of next-generation vaccines against the junctional region (Atcheson et al, 2021;Calvo-Calle et al, 2021;Francica et al, 2021;Jelı ´nkova ´et al, 2021).…”

The light chain of the L9 antibody is critical for binding circumsporozoite protein minor repeats and preventing malaria

“…However, the isolation of rare and potent mAbs that preferentially bind NPDP (Kisalu et al, 2018;Tan et al, 2018) or the NVDP repeats (Wang et al, 2020) identified these subdominant epitopes as new sites of vulnerability on PfCSP. As these epitopes are not contained in RTS,S, these discoveries led to the development of nextgeneration vaccines against the junctional region (Atcheson et al, 2021;Calvo-Calle et al, 2021;Francica et al, 2021;Jelínková et al, 2021).…”