Viral vectored transmission blocking vaccines against Plasmodium falciparum

Background: Transmission blocking vaccines (TBVs) target sexual develop¬ment of the parasite within the mosquito and aim to prevent transmission of malaria from one individual to another. Antibodies raised against Pfs48/45, Pfs230 Region C, PfHAP2, and Anopheles gambiae Alanyl Aminopeptidase N1 (AgAPN1) proteins reduce transmission i.e. have transmission blocking activity [1–5]. Recombinant simian Adenovirus (AdC63 serotype) and Modified Vaccinia Ankara (MVA) viral vectors have been shown to induce high antibody titres to asexual parasite antigens in animal studies [6]. Materials and methods: Protein sequences for each of the antigens were codon optimised for expression in humans and cloned into shuttle vectors, which were then recombined with the parental virus and purified to obtain virus expressing the antigen of interest. Mice were vaccinated with AdC63 (i.m.), sera was taken after 2 weeks, and will be followed by an MVA boost (i.d.) eight weeks after the prime. Antibodies were assayed by a standardised ELISA, and transmission blocking activity assessed using a standardised membrane feeding assay (SMFA). Conclusion: Induction of high antibody tires using this vaccine platform could be used together with other control measures to achieve elimination and/or eradication of the disease at a local or national level

Adenovirus-prime and baculovirus-boost heterologous immunization achieves sterile protection against malaria sporozoite challenge in a murine model.

With the increasing prevalence of artemisinin-resistant malaria parasites, a highly efficacious and durable vaccine for malaria is urgently required. We have developed an experimental virus-vectored vaccine platform based on an envelope-modified baculovirus dual-expression system (emBDES). Here, we show a conceptually new vaccine platform based on an adenovirus-prime/emBDES-boost heterologous immunization regimen expressing the Plasmodium falciparum circumsporozoite protein (PfCSP). A human adenovirus 5-prime/emBDES-boost heterologous immunization regimen consistently achieved higher sterile protection against transgenic P. berghei sporozoites expressing PfCSP after a mosquito-bite challenge than reverse-ordered or homologous immunization. This high protective efficacy was also achieved with a chimpanzee adenovirus 63-prime/emBDES-boost heterologous immunization regimen against an intravenous sporozoite challenge. Thus, we show that the adenovirus-prime/emBDES-boost heterologous immunization regimen confers sterile protection against sporozoite challenge by two individual routes, providing a promising new malaria vaccine platform for future clinical use

Poor CD4+ T Cell Immunogenicity Limits Humoral Immunity to P. falciparum Transmission-Blocking Candidate Pfs25 in Humans.

Plasmodium falciparum transmission-blocking vaccines (TBVs) targeting the Pfs25 antigen have shown promise in mice but the same efficacy has never been achieved in humans. We have previously published pre-clinical data related to a TBV candidate Pfs25-IMX313 encoded in viral vectors which was very promising and hence progressed to human clinical trials. The results from the clinical trial of this vaccine were very modest. Here we unravel why, contrary to mice, this vaccine has failed to induce robust antibody (Ab) titres in humans to elicit transmission-blocking activity. We examined Pfs25-specific B cell and T follicular helper (Tfh) cell responses in mice and humans after vaccination with Pfs25-IMX313 encoded by replication-deficient chimpanzee adenovirus serotype 63 (ChAd63) and the attenuated orthopoxvirus modified vaccinia virus Ankara (MVA) delivered in the heterologous prime-boost regimen via intramuscular route. We found that after vaccination, the Pfs25-IMX313 was immunologically suboptimal in humans compared to mice in terms of serum Ab production and antigen-specific B, CD4+ and Tfh cell responses. We identified that the key determinant for the poor anti-Pfs25 Ab formation in humans was the lack of CD4+ T cell recognition of Pfs25-IMX313 derived peptide epitopes. This is supported by correlations established between the ratio of proliferated antigen-specific CD4+/Tfh-like T cells, CXCL13 sera levels, and the corresponding numbers of circulating Pfs25-specific memory B cells, that consequently reflected on antigen-specific IgG sera levels. These correlations can inform the design of next-generation Pfs25-based vaccines for robust and durable blocking of malaria transmission

Safety and Immunogenicity of ChAd63/MVA Pfs25-IMX313 in a Phase I First-in-Human Trial.

BACKGROUND: Transmission blocking vaccines targeting the sexual-stages of the malaria parasite could play a major role to achieve elimination and eradication of malaria. The Plasmodium falciparum Pfs25 protein (Pfs25) is the most clinically advanced candidate sexual-stage antigen. IMX313, a complement inhibitor C4b-binding protein that forms heptamers with the antigen fused to it, improve antibody responses. This is the first time that viral vectors have been used to induce antibodies in humans against an antigen that is expressed only in the mosquito vector. METHODS: Clinical trial looking at safety and immunogenicity of two recombinant viral vectored vaccines encoding Pfs25-IMX313 in healthy malaria-naive adults. Replication-deficient chimpanzee adenovirus serotype 63 (ChAd63) and the attenuated orthopoxvirus modified vaccinia virus Ankara (MVA), encoding Pfs25-IMX313, were delivered by the intramuscular route in a heterologous prime-boost regimen using an 8-week interval. Safety data and samples for immunogenicity assays were taken at various time-points. RESULTS: The reactogenicity of the vaccines was similar to that seen in previous trials using the same viral vectors encoding other antigens. The vaccines were immunogenic and induced both antibody and T cell responses against Pfs25, but significant transmission reducing activity (TRA) was not observed in most volunteers by standard membrane feeding assay. CONCLUSION: Both vaccines were well tolerated and demonstrated a favorable safety profile in malaria-naive adults. However, the transmission reducing activity of the antibodies generated were weak, suggesting the need for an alternative vaccine formulation. TRIAL REGISTRATION: Clinicaltrials.gov NCT02532049

Human vaccination against RH5 induces neutralizing antimalarial antibodies that inhibit RH5 invasion complex interactions.

The development of a highly effective vaccine remains a key strategic goal to aid the control and eventual eradication of Plasmodium falciparum malaria. In recent years, the reticulocyte-binding protein homolog 5 (RH5) has emerged as the most promising blood-stage P. falciparum candidate antigen to date, capable of conferring protection against stringent challenge in Aotus monkeys. We report on the first clinical trial to our knowledge to assess the RH5 antigen - a dose-escalation phase Ia study in 24 healthy, malaria-naive adult volunteers. We utilized established viral vectors, the replication-deficient chimpanzee adenovirus serotype 63 (ChAd63), and the attenuated orthopoxvirus modified vaccinia virus Ankara (MVA), encoding RH5 from the 3D7 clone of P. falciparum. Vaccines were administered i.m. in a heterologous prime-boost regimen using an 8-week interval and were well tolerated. Vaccine-induced anti-RH5 serum antibodies exhibited cross-strain functional growth inhibition activity (GIA) in vitro, targeted linear and conformational epitopes within RH5, and inhibited key interactions within the RH5 invasion complex. This is the first time to our knowledge that substantial RH5-specific responses have been induced by immunization in humans, with levels greatly exceeding the serum antibody responses observed in African adults following years of natural malaria exposure. These data support the progression of RH5-based vaccines to human efficacy testing

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Development and assessment of particular transmission-blocking malaria vaccines

Transmission-blocking vaccines (TBVs) target Plasmodium parasite sexual stages, aiming to block further development of the parasite within the mosquito host. Plasmodium falciparum zygote/ookinete surface protein Pfs25 is one of the leading TBV candidate antigens and antibodies against Pfs25 have been shown to exhibit complete transmission-blocking activity in pre-clinical studies. Phase 1 human clinical trials have revealed that Pfs25 was a poor immunogen in humans in the formulations tested and high titers of anti-Pfs25 antibodies are required to achieve good transmission-blocking activity in the ex vivo standard membrane feeding assay which measures the functional activity of the antibodies induced. Work in this thesis describes the production of recombinant monomeric Pfs25 protein, Pfs25 based particulate vaccines (Pfs25-IMX313 nanoparticle, Pfs25-HBsAg VLP and Pfs25-Qβ VLP) and a Pfs25-Pfs28 multivalent protein vaccine in the Pichia pastoris protein expression system. These proteins were tested in mice using protein-in-adjuvant formulations and their immunogenicity was assessed. Pfs25-IMX313 nanoparticle induced significantly higher anti-Pfs25 antibodies than monomeric Pfs25 and the antibodies had higher avidity and transmission-blocking activity. All of the candidate vaccines generated, except for Pfs25-HBsAg VLP, were immunogenic. The Pfs25-IMX313 nanoparticle induced the highest antibody response in mice followed by the Pfs25-Pfs28 multivalent protein and Pfs25-Qβ VLP.This thesis is not currently available via ORA