Immunofocusing humoral immunity potentiates the functional efficacy of the AnAPN1 malaria transmission-blocking vaccine antigen

Abstract

Malaria transmission-blocking vaccines (TBVs) prevent the completion of the developmental lifecycle of malarial parasites within the mosquito vector, effectively blocking subsequent infections. The mosquito midgut protein Anopheline alanyl aminopeptidase N (AnAPN1) is the leading, mosquito-based TBV antigen. Structure-function studies identified two Class II epitopes that can induce potent transmission-blocking (T-B) antibodies, informing the design of the next-generation AnAPN1. Here, we functionally screened new immunogens and down-selected to the UF6b construct that has two glycine-linked copies of the T-B epitopes. We then established a process for manufacturing UF6b and evaluated in outbred female CD1 mice the immunogenicity of the preclinical product with the human-safe adjuvant Glucopyranosyl Lipid Adjuvant in a liposomal formulation with saponin QS21 (GLA-LSQ). UF6b:GLA-LSQ effectively immunofocused the humoral response to one of the key T-B epitopes resulting in potent T-B activity, underscoring UF6b as a prime TBV candidate to aid in malaria elimination and eradication efforts.

Immunopotentiation by Lymph-Node Targeting of a Malaria Transmission-Blocking Nanovaccine

“…Previously we have shown that the UF6b antigen is highly immunogenic in CD1 outbred mice (8). Here we aimed to find the optimally immunogenic dose and ratio of UF6b-NPs to CpG-NPs.…”

“…The ELISAs were performed as previously described (8). Briefly, Nunc Maxisorp 96-well ELISA plates (Fisher Scientific, Waltham, MA, USA) were incubated overnight at 4°C with 1 mg/mL UF6b antigen in 0.1×PBS (pH 7.2).…”

“…The isotype of the UF6b-specific elicited antibody was determined using a Mouse Typer Isotyping Panel (Bio-Rad) as previously described (8). Briefly, plates were coated and blocked as described above.…”

“…Parallel structure-based studies identified the T-B epitopes as peptides 7 and 9 (6). To focus the immune response to the key T-B epitopes we developed a new, purification tag-free AnAPN1 construct, UF6b, containing two copies of peptides 2-9 connected by a glycine linker (8). This new construct can be produced at scale and was shown to be highly immunogenic in outbred CD1 mice immunized intramuscularly (i.m.)…”

“…This new construct can be produced at scale and was shown to be highly immunogenic in outbred CD1 mice immunized intramuscularly (i.m.) with UF6b formulated with the human-safe adjuvant Glucopyranosyl Lipid Adjuvant in a liposomal formulation with saponin QS21 (GLA-LSQ), eliciting a focused peptide 9 specific response resulting in potent T-B antibodies (6,8).…”