Introduction and Background of the Project

Introduction

Malaria continues to be a major global health problem, and economic burden in disease-endemic countries. For 2016 alone, the WHO reported some 214 million cases worldwide and about 445,000 deaths, mostly among children under the age of five. With almost half of the world’s population at risk, the public health community has once again rallied around the goal of malaria elimination and eradication.

Malaria develops after the transmission of Plasmodium parasites from infected Anopheles mosquitoes (the vector for the disease) to humans as part of a complex life cycle that requires different developmental stages in the mosquito and humans. Most cases of malaria are caused by two out of five infectious Plasmodium species, P. falciparum, which is dominant in large parts of Africa, and P. vivax, which is predominant throughout Asia and the Americas.

As a result of the effort to reduce global malaria burdens, the new-case rate fell by 37% between 2000 and 2015; this led to an even greater reduction (an impressive 60%) in the malaria death rate globally over all age groups. However, insecticide resistant mosquitoes and antimalarial drug resistant parasites are challenging the success of malaria elimination efforts. Therefore, new tools are urgently needed to effectively block the transmission of the parasite to further reduce the number of new cases and overall disease prevalence with the aim of finally eradicating malaria entirely.

Project objective

A very promising approach to reduce malaria transmission is the development of so-called “Transmission Blocking Vaccines” or “TBVs” that could block the transmission of the parasite from humans to the mosquito. Targeted vaccination of individuals in high transmission areas promise an immediate and effective reduction in the number of malaria cases.  Although a TBV would not directly prevent immunized individuals from developing the disease, it has a clear, delayed clinical benefit for the population as a whole. Moreover, a TBV could provide effective means to prevent the spread of antimalarial drug-resistant parasites, and parasites that break through the most advanced malaria vaccine (Mosquirix™) to date. Thus, the development of new TBVs is one of the research priorities for a cost effective intervention that can directly support the malaria eradication effort. The development of TBVs has mostly focused on P. falciparum ookinete surface protein 25 (Pfs25) and its P. vivax homolog Pvs25, for which Phase 1 clinical trials have been initiated, as well as gametocyte proteins such as Pfs48/45 and Pfs230. However, successful suppression of malaria transmission in most parts of the world will require TBVs that effectively block transmission of both P. falciparum and P. vivax, as the most common causes of disease. A parasite-centric approach requires the development of multiple TBVs using protein immunogens from different species. Instead, we focused our studies on developing a vaccine based on a highly conserved mosquito protein that acts as a receptor for the parasite, and has the potential to block malaria transmission regardless of the Plasmodium species, i.e., a so-called universal malaria TBV.

Project design

The Anopheline mosquito midgut-specific alanyl aminopeptidase N (AnAPN1) is a luminal midgut surface protein involved in blood meal digestion. At present, AnAPN1 is the only TBV candidate, which blocks parasite transmission of P. falciparum and P. vivax in different Anopheles species. Working with a mosquito protein further reduces the risk that the parasite could develop resistance against the intervention, potentially allowing for a long-term use of the vaccine under elimination settings.

AnAPN1 has been studied extensively in transmission-blocking experiments, where the protein induced very high titers in immunized animals. Antibodies elicited against specific epitopes of AnAPN1 completely reduced parasite development in the mosquito. Detailed analysis of the protein structure and consecutive mapping of epitope domains identified different antigenic regions within the full-length protein, out of which only one domain is required for blocking transmission. Since any TBV will require very high antibody titers within vaccinated individuals to be effective, it is mandatory to develop well-defined antigens comprising only the domain required for transmission blocking activity, while avoiding the triggering of an immune response against regions that do not contribute to transmission blocking activity.  We have achieved this goal, by re-designing the AnAPN1 antigen and immuno-focusing the humoral response to the key epitopes.  The new AnAPN1 immunogen, UF6, when formulated with the GLA-LSQ adjuvant elicits potent transmission-blocking activity against natural P. falciparum strains.

In a joint effort by the University of Florida, CellFree Sciences Co., Ltd., Ology Bioservices, Hamamatsu Pharma Research, Inc., IDRI (the Infectious Disease Research Institute), and the Centre Pasteur du Cameroon, our project aims to accelerate AnAPN1 vaccine development via a process development and clinical manufacturing program with clear Go/No-Go milestones over two years.  This effort includes quality control checkpoints, scale-up production of the UF6 candidate antigen and validation of product using various immunological and functional assays. The UF6:GLA-LSQ vaccine formulation will be tested in mice and non-human primates.  Antibodies obtained from these animals will be fully evaluated using a set of functional immunological and biological in vivo assays established at the University of Florida and Centre Pasteur du Cameroon.

How can your partnership (project) address global health challenges?

AnAPN1 has been extensively studied in transmission-blocking experiments, where the immunogen induced very high titers in immunized animals. Antibodies raised against AnAPN1 in those animals greatly reduced parasite development in the mosquito and thus subsequently blocked the cascade of secondary infection of other individuals. The locus encoding the AnAPN1 protein is highly conserved in the genome of different Anopheles mosquito species suggesting that an AnAPN1-derived TBV could be effectively used in different areas regardless of the local vectors. Along with its ability to block transmission of P. falciparum and P. vivax, an AnAPN1-derived TBV therefore has the potential to be globally applied for the control of malaria transmission regardless of the parasite and mosquito species combination in local settings. Working with a mosquito protein further reduces the risk that the parasite could develop resistance against the intervention, potentially allowing for a long-term use of the vaccine under eradication settings. We anticipate that the project will allow us to transition to the second phase of our program, including the conduct of current Good Manufacturing Practices (cGMP)-compliant Drug Substance (DS) and Drug product (DP) production and acquiring regulatory support of the UF6-AnAPN1 vaccine candidate for use in first-in-human trials. The impact of a mosquito-based TBV on global health and malaria elimination is profound.  In the short-term, if delivered in tandem with Mosquirix™ or another vaccine, it can provide synergistic reduction in the total number of new cases (disease incidence) of malaria.  Importantly, TBVs in the near term can extend the efficacy of artemisinin-based combination therapies, by reducing the spread of drug-resistant parasites from Southeast Asia to Africa and beyond.  In the long term, once malaria is controlled in a specific region, and there is a predominance of asymptomatic carriage that can lead to epidemic malaria, the TBV can be used in a top-down approach to wipe out the last vestiges of parasite reservoirs in the human population. Importantly, TBVs offer immediate benefits to the population by reducing infection rates in households and communities during and beyond the malaria transmission season.  Protection can be further extended by combining TBV delivery with another malaria vaccine or administration of artemisinin-combined therapy to wipe out low-level parasitemia.

What sort of innovation are you bringing in your project?

Shifting the focus of TBV development from the use of parasite proteins towards the mosquito-derived AnAPN1 protein offers a number of principle advantages for blocking the transmission of multiple Plasmodium species on a global scale by a single TBV. AnAPN1-derived antibodies have already been demonstrated to reduce, if not completely block the transmission of P. falciparum and P. vivax. We previously applied a structure-guided vaccine design strategy to produce the optimized AnAPN1 vaccine antigen UF6 and used animal-mosquito-animal transmission models to quantify the impact of this TBV antigen on parasite transmission. During the preclinical development stage, studies with UF6 and the adjuvant GLA-LSQ will be extended to non-human primates and proof-of-concept experiments to allow better prediction of the efficacy of the TBV in malaria endemic regions.

Role and Responsibility of Each Partner

1. University of Florida, UF: Overall project management and proposal design, mAb development, mouse immunization studies, immunological assays, direct membrane feeding assays conducted in Cameroon (in collaboration with CPC).  UF, as the primary Development Partner will be coordinating and managing the scope of activities across all activities/milestones outlined for this project.  Specific capacities at UF include the immunization and functional studies (IFS) in rodents and the evaluation of transmission-blocking activity of antisera raised against the scaled-up/optimized UF6 immunogen formulated with GLA-LSQ adjuvant.

2. Ology Bioservices:  Proposal design, process development, pre/clinical manufacturing, QA/QC, report provision. Ology is the primary CRO responsible for preclinical immunogen production.

3. Hamamatsu Pharma Research, Inc., HPR: Proposal design/consultation and implementation of non-human primate (NHP), non-GLP immunization study (durability of immune response study), report provision. 

4. CellFree Sciences, Co. Ltd., CFS: Proposal design/consultation and production of small- scale UF6 protein lot for comparative testing with those produced by Ology Bioservices in this project.

5. IDRI (Infectious Disease Research Institute):  Proposal design, GLA-LSQ provision (vialed), consultation for immunization studies and strategy for the subsequent phase of development. 

6. Centre Pasteur du Cameroon, CPC: Direct Membrane Feeding Assays (DMFA) and Human Subjects Research IRB monitoring and compliance.

The Imperial College London will be providing collaborating support for the analysis and statistical modeling of animal-mosquito-animal transmission-study data under AnAPN1 TBV control.

Others (including references if necessary)

On malaria:

World malaria report 2017

29 November 2017 On AnAPN1:

The Anopheles-midgut APN1 structure reveals a new malaria transmission-blocking vaccine epitope.

Atkinson SC, Armistead JS, Mathias DK, Sandeu MM, Tao D, Borhani-Dizaji N, Tarimo BB, Morlais I, Dinglasan RR, Borg NA.

Nat Struct Mol Biol. 2015 Jul;22(7):532-9. doi: 10.1038/nsmb.3048. Epub 2015 Jun 15.

Antibodies to a single, conserved epitope in Anopheles APN1 inhibit universal transmission of Plasmodium falciparum and Plasmodium vivax malaria.

Armistead JS, Morlais I, Mathias DK, Jardim JG, Joy J, Fridman A, Finnefrock AC, Bagchi A, Plebanski M, Scorpio DG, Churcher TS, Borg NA, Sattabongkot J, Dinglasan RR.

Infect Immun. 2014 Feb;82(2):818-29. doi: 10.1128/IAI.01222-13. Epub 2013 Dec 9.

Disruption of Plasmodium falciparum development by antibodies against a conserved mosquito midgut antigen.

Dinglasan RR, Kalume DE, Kanzok SM, Ghosh AK, Muratova O, Pandey A, Jacobs-Lorena M.

Proc Natl Acad Sci U S A. 2007 Aug 14;104(33):13461-6. Epub 2007 Aug 2.

Final Report

1. Project objective

The objective of this project is to develop a pan-malaria transmission-blocking vaccine, a cost-effective intervention that can reduce on-going transmission as well as the cascade of new infections. The vaccine antigen is the Anopheles mosquito midgut protein (AnAPN1), which is a putative receptor for malaria parasites that is highly conserved across malaria mosquito vectors around the globe. This project will develop a process development plan for cGMP production of the second generation of the AnAPN1 vaccine formulated with the potent and human safe GLA-LSQ adjuvant.

2. Project design

In the two-year project, we executed the first phase of  process development tasks of a two-phase strategy: (a) Analytical Method Technology Transfer & Validation, (b) Process Technology Transfer, (c) cGMP Master Cell Banking, and (d) Scale-up & Optimization to produce a Non-cGMP bulk drug substance. Importantly, we also performed in-process testing of the antigen in short and long-term immunological studies in mice and non-human primates, respectively. Antisera generated in these animal models were used to measure functional antigen-specific antibody titers and transmission-blocking activity against Plasmodium falciparum through laboratory as well as field-based mosquito feeding assays in Cameroon.

3. Results, lessons learned

A reproducible process development pipeline to produce an untagged AnAPN1 antigen at large scale under cGMP standards was established. The products of this project include bulk drug substance and importantly, a well-characterized Master Cell Bank for the vaccine antigen, which will facilitate subsequent production of drug product for first in human trials. We tested two different immunization regimens in mice and measured antibody titers with functional transmission-blocking activity in our two complementary malaria mosquito feeding assays. The vaccine durability study in non-human primates (NHP) confirmed immune recall after 360 days following either a single dose or two doses spaced 8 weeks apart. NHPs that received only a single immunization were able to generate a second rapid increase in antibodies production, suggesting that in real-world scenarios wherein an individual fails to receive the complete vaccine dose series for any number of reasons, will still be able to amount an antibody response when they receive a boosting dose a year later. A comparison of the immunological data from the NHP and mice studies suggest that overall antibody titers alone are not predictive of transmission-blocking activity in our assays, but the quality of the antibody is more important. NHP antibody titers never reached those observed in the mouse study but were nonetheless comparable in transmission-blocking activity. These data will be important in informing clinical studies. The current bulk drug substance has very favorable characteristics, including zero bioburden and a relatively high yield (3 grams/120 L scale) of purified, untagged antigen with acceptable endotoxin levels for use in human studies. To move forward towards first in human studies, we envision that the second phase (clinical manufacturing) will include the following tasks: (a) cGMP Drug Substance Manufacturing, (b) Drug Project (DP) Engineering Runs, (c) cGMP DP Run with Fill & Finish, and (d) Regulatory Support leading to a Phase 1 clinical study in Sub-Saharan Africa.