Biology subjects

Long, C. A.

Publications and source records attributed to Long, C. A..

7 recordsLinked to original sources

bioRxiv2024

Development of an improved blood-stage malaria vaccine targeting the essential RH5-CyRPA-RIPR invasion complex

In recent years, reticulocyte-binding protein homologue 5 (RH5) has emerged as a leading blood-stage Plasmodium falciparum malaria vaccine antigen. The most advanced blood-stage vaccine candidate in a Phase 2b clinical trial, RH5.1/Matrix-M, is based on a full-length soluble protein-with-adjuvant formulation. RH5 interacts with cysteine-rich protective antigen (CyRPA) and RH5- interacting protein (RIPR) to form an essential heterotrimeric "RCR-complex". Here, we investigated whether a vaccine candidate based on the ternary RCR-complex could substantially improve upon the leading clinical candidate RH5.1/Matrix-M in preclinical studies. Using a panel of monoclonal antibodies (mAbs) we confirm that parasite growth-inhibitory epitopes on each antigen are exposed on the surface of the RCR-complex and that mAb pairs binding to different antigens can function additively or synergistically to mediate parasite growth inhibition activity (GIA) in vitro. However, immunisation of rats with the RCR-complex consistently fails to outperform RH5.1 alone. We show this is due to immuno-dominance of RIPR coupled with the inferior potency of anti-full length RIPR polyclonal IgG antibodies as compared to the anti-RH5 and anti-CyRPA response. To address this, we identified the growth-inhibitory antibody epitopes of RIPR are clustered within C-terminal EGF-like domains of RIPR. A fusion of these EGF domains to CyRPA, called "R78C", combined with RH5.1, provided a new vaccination strategy that improves upon the levels of in vitro GIA seen with RH5.1 alone. Superiority of the combination antigen vaccine candidate was achieved by the induction of a quantitatively higher, but qualitatively similar, polyclonal antibody response that demonstrated additive GIA across the three antigen targets. These preclinical data justified the advancement of the RH5.1+R78C/Matrix-M combination vaccine to a Phase 1 clinical trial.

immunology↗

bioRxiv2024

Evaluation of Precision of the Plasmodium knowlesi Growth Inhibition Assay for Plasmodium vivax Duffy-Binding Protein-based Malaria Vaccine Development

Recent data indicate increasing disease burden and importance of Plasmodium vivax (Pv) malaria. A robust assay will be essential for blood-stage Pv vaccine development. Results of the in vitro growth inhibition assay (GIA) with transgenic P. knowlesi (Pk) parasites expressing the Pv Duffy-binding protein region II (PvDBPII) correlate with in vivo protection in the first PvDBPII controlled human malaria infection (CHMI) trials, making the PkGIA an ideal selection tool once the precision of the assay is defined. To determine the precision in percentage of inhibition in GIA (%GIA) and in GIA50 (antibody concentration that gave 50 %GIA), ten GIAs with transgenic Pk parasites were conducted evaluating four different anti-PvDBPII human monoclonal antibodies (mAbs) at different concentrations, and three GIAs were conducted testing eighty anti-PvDBPII human polyclonal antibodies (pAbs) at 10 mg/mL. A significant assay-to-assay variation was observed, and the analysis revealed a standard deviation (SD) of 13.1 in the mAb and 5.94 in the pAb dataset for %GIA, with a LogGIA50 SD of 0.299 (for mAbs). Moreover, the ninety-five percent confidence interval (95%CI) for %GIA or GIA50 in repeat assays was calculated in this investigation. These results will support the development of future blood-stage malaria vaccines, specifically second generation PvDBPII-based formulations.

immunology↗

bioRxiv2024

Preclinical Development of a Stabilized RH5 Virus-Like Particle Vaccine that Induces Improved Anti-Malarial Antibodies

The development of a highly effective vaccine against the pathogenic blood-stage infection of human malaria will require a delivery platform that can induce an antibody response of both maximal quantity and functional quality. One strategy to achieve this includes presenting antigens to the immune system on virus-like particles (VLPs). Here we sought to improve the design and delivery of the blood-stage Plasmodium falciparum reticulocyte-binding protein homolog 5 (RH5) antigen, which is currently in a Phase 2 clinical trial as a full-length soluble protein-in-adjuvant vaccine candidate called RH5.1/Matrix-M. We identify disordered regions of the full-length RH5 molecule induce non-growth inhibitory antibodies in human vaccinees, and a re-engineered and stabilized immunogen that includes just the alpha-helical core of RH5 induces a qualitatively superior growth-inhibitory antibody response in rats vaccinated with this protein formulated in Matrix-M adjuvant. In parallel, bioconjugation of this new immunogen, termed "RH5.2", to hepatitis B surface antigen VLPs using the "plug-and-display" SpyTag-SpyCatcher platform technology also enabled superior quantitative antibody immunogenicity over soluble antigen/adjuvant in vaccinated mice and rats. These studies identify a new blood-stage malaria vaccine candidate that may improve upon the current leading soluble protein vaccine candidate RH5.1/Matrix-M. The RH5.2-VLP/Matrix-M vaccine candidate is now under evaluation in Phase 1a/b clinical trials.

immunology↗

bioRxiv2023

Natural malaria infection elicits rare but potent neutralizing antibodies to the blood-stage antigen RH5

Plasmodium falciparum RH5 is the most advanced blood-stage malaria vaccine candidate and is under evaluation for efficacy in endemic regions, emphasizing the need to study the underlying antibody response to RH5 during natural infection. Here, we found that RH5-reactive B cells were rare in malaria-exposed individuals despite repeated infections over multiple years. RH5-specific monoclonal antibodies isolated from these individuals were extensively mutated but mostly targeted non-neutralizing epitopes, in contrast to antibodies from RH5-vaccinated, malaria-naive individuals. However, infection-derived MAD8-151 and MAD8-502 were among the most potent neutralizers out of 186 antibodies isolated from both cohorts and target the same epitopes as the most effective vaccine-induced antibodies. Binding to basigin receptor-proximal epitopes was the primary factor governing the potency of RH5-specific antibodies from both natural infection and vaccination, followed by the strength of binding. These results indicate a clear strategy for the development of next-generation RH5 vaccines for use in malaria-endemic regions.

immunology↗

bioRxiv2023

Analysis of the Diverse Antigenic Landscape of the Malaria Invasion Protein RH5 Identifies a Potent Vaccine-Induced Human Public Antibody Clonotype

The highly conserved and essential Plasmodium falciparum reticulocyte-binding protein homolog 5 (PfRH5) has emerged as the leading target for vaccines that seek to protect against the disease-causing blood-stage of malaria. However, the features of the human vaccine-induced antibody response that confer highly potent inhibition of malaria parasite invasion into red blood cells are not well defined. Here we characterize over 200 human IgG monoclonal antibodies induced by the most advanced PfRH5 vaccine. We define the antigenic landscape of this molecule, and establish epitope specificity, antibody association rate and intra-PfRH5 antibody interactions are key determinants of functional anti-parasitic potency. In addition, we identify a germline gene combination that results in an exceptionally potent class of antibody and demonstrate its prophylactic potential to protect against P. falciparum parasite challenge in vivo. This comprehensive dataset provides a framework to guide rational design of next-generation vaccines and prophylactic antibodies to protect against blood-stage malaria.

immunology↗

bioRxiv2020

Plasmodium falciparum population genetic complexity influences transcriptional profile and immune recognition of highly related genotypic clusters

As transmission intensity has declined in Senegal, so has the genetic complexity of circulating Plasmodium falciparum parasites, resulting in specific genotypes emerging and persisting over years. We address whether changes in parasite genetic signatures can alter the immune repertoire to variant surface antigens, and whether such responses can influence the expansion or contraction of specific parasite genotypes in the population. We characterize parasites within genotypic clusters, defined as identical by a 24-SNP molecular barcode and a haplotype identifier for other highly polymorphic loci; we measure expression of variant surface antigens (VSA) such as PfEMP-1 by transcript expression typing and expressed var DBL1 sequencing in ex vivo and short-term adapted RNA samples; and we measure IgG responses against VSAs from short-term adapted parasites. We find that parasites within genotypic clusters are genetically identical at other highly polymorphic loci. These parasites express similar Ups var classes and largely the same dominant var DBL1 sequences ex vivo. These parasites are recognized similarly by anti-VSA antibodies after short-term adaptation to culture; however, antibody responses do not correlate with genotype frequencies over time. Both genotype-specific and multiple genotype-reactive surface IgG responses are observed in this population. Parasites with identical genomes are extremely similar in their expression and host antibody recognition of VSAs. Monitoring changes in population-level parasite genomics and transmission dynamics is critical, as fluctuations will influence the breadth of resulting host immune responses to circulating parasite genotypes. These findings suggest shared immune recognition of genetically similar parasites, which has implications for both our understanding of immunity and vaccine development strategies in malaria elimination settings.

microbiology↗

bioRxiv2019

Malaria vaccine candidates displayed on novel virus-like particles are immunogenic and induce transmission-blocking activity

The development of effective malaria vaccines remains a global health priority. Currently, the most advanced vaccine, known as RTS,S, has only shown modest efficacy in clinical trials. Thus, the development of more efficacious vaccines by improving the formulation of RTS,S for increased efficacy or to interrupt malaria transmission are urgently needed. The RTS,S vaccine is based on the presentation of a fragment of the sporozoite antigen on the surface of virus-like particles (VLPs) based on human hepatitis B virus (HBV). In this study, we have developed and evaluated a novel VLP platform based on duck HBV (known as Metavax) for malaria vaccine development. This platform can incorporate large and complex proteins into VLPs and is produced in a Hansenula cell line compatible with cGMP vaccine production. Here, we have established the expression of leading P. falciparum malaria vaccine candidates as VLPs. This includes Pfs230 and Pfs25, which are candidate transmission-blocking vaccine antigens. We demonstrated that the VLPs effectively induce antibodies to malaria vaccine candidates with minimal induction of antibodies to the duck-HBV scaffold antigen. Antibodies to Pfs230 also recognised native protein on the surface of gametocytes, and antibodies to both Pfs230 and Pfs25 demonstrated transmission-reducing activity in standard membrane feeding assays. These results establish the potential utility of this VLP platform for malaria vaccines, which may be suitable for the development of multi-component vaccines that achieve high vaccine efficacy and transmission-blocking immunity.

immunology↗