Science & Pipeline
Developing malaria vaccines using insights from human malaria immunity
The scientific strategy and the clinical approach used to discover our lead candidates are unlike that of most other malaria vaccines.
Competing candidates are constrained by heavy dependence on clues derived from animal malaria and uncertainty over mechanism of action, which is an obstacle to designing effective vaccines.
A Unique Approach
This is in contrast with Vac4All’s approach, which has capitalized on the remarkable opportunity presented by the fact that humans can acquire protection against malaria, either by natural exposure (blood-stages) or by artificial exposure to sporozoites (pre-erythrocytic stages).
These observations are at the heart of the discovery of our vaccine antigens. Investigation of this clinical immunity led to identify underlying mechanisms of biological action. These mechanisms were in turn instrumental in identifying Vac4All leading candidates MSP3, LSA3 and LSA5.
The responses have guided development with methods that no other developers are fully exploiting, giving our company a major competitive advantage.
Science & Pipeline
Innovation & Competitive Edge
Vac4All’s competitive edge can be summarized by 2 elements
1- A Unique Approach
Human malaria parasites only infect humans and therefore rodent models are not relevant. In contrast to the vast majority of research performed in mice, which led to develop many vaccines efficient against rodent but not human malaria, we reflected that:
A- Humans acquire immunity against Malaria
- Naturally by exposure in endemic areas
- Artificially by irradiated mosquitoes bites
B- Therefore, our vaccine strategy is based on exploiting this characteristic, which have been surprisingly little tapped by others.
2- Strategy: Alliance with a powerful industrial partner to ensure registration and marketing
The Sanofi-Vac4All partnership brings together:
- the innovation of a start-up with the ability to bring to market of a big Pharma;
- the active participation of Sanofi, the biggest vaccine manufacturer, is an enormous and unusual asset.
Summary of Scientific Competitive Advantages
Vac4All’s scientific competitive edge is summarized in the table above and can be described under the following 4 scientific and technical assets :
1. Antigen selection based on human immunity to malaria
Vac4All’s portfolio of candidate-vaccines, based on the antigens MSP3, LSA3 and LSA5, results from decades of research into human malaria immunity. By examining the types of clinical malaria immunity, we identified novel mechanisms and important molecules we believe to be responsible for malaria immunity in humans. These immune mechanisms were then used to guide the discovery, design and development of Vac4All’s vaccine pipeline. In-house analytical knowledge and tools were developed and refined in the process, allowing Vac4All control over the selection and testing of candidate-vaccine molecules.
2. Proven safety, immunogenicity and efficacy of first-generation prototypes
From clinical testing of first-generation candidate vaccine prototypes – MSP3-LSP vaccine for ADAMVAX, LSA3-FL for STOPMAL and LSA5 that covers both mechanisms of action – Vac4All has gathered proof that its vaccine molecules are safe and immunogenic. For MSP3-LSP, efficacy in children was demonstrated. Above all, results also support the hypothesized biological mechanisms behind the discovery of the vaccine molecules. This in turn allows the design of greatly improved second-generation vaccines with more certainty.
3. Biomarker-driven design and development based on immunological mechanism of protection of humans
Our mechanism of action approach is unique in the malaria vaccine development sector and our biomarkers assays are an important differentiating advantage that leads to de-risking our pipeline and towards successful development. Our past R&D know-how and data from previous clinical testing allow development to be benchmarked and stage-gated efficiently and appropriately.
4. Technology platform with low safety and regulatory barriers
- Biofusion conjugate technology
- Alum first formulation
We have deliberately chosen and executed a technical strategy of seeking technological platforms with low safety risk and low regulatory barrier. By researching, selecting and using tried and true licensed technologies, we have an enormous head start as it minimizes manufacturing, safety and regulatory risks, compared to the use of novel adjuvants or viral vectors favored by our competitors. In addition, this broadly accepted approach guarantees easy uptake and distribution in the target populations.
Vac4All’s second-generation candidates have been optimized using innovative strategies which include:
- Adding a carrier protein (CP) to generate the optimal vaccine responses needed to our vaccines;
- Tailoring vaccine constructs with immunogenicity and antigenicity analysis to identify and excise immune-regulatory regions;
- Inventing a novel production technique using bio-conjugation: this modification, which we patented, leads to cut cost of goods tremendously;
- Improving our vaccine molecule screening capabilities through the development of a unique mouse model we call the “human immunogenicity” mouse model (HIMM)
Science & Pipeline
Summary of advantages:
- All antigens discovered using human immune responses;
- Vac4All candidates are Antigenic and Immunogenic;
- Antigens shown to confer protection in preclinical models;
- Vaccine antigens are highly conserved;
- Second-generation biofusion vaccines show much greater immunogenicity and duration of immune responses compared to first-generation prototypes.
Our candidate malaria vaccines aim to induce immune mechanisms of action that will kill specific malaria parasite stages.
Our sporozoite and liver-blocking anti-malaria vaccines (STOPMAL antigens LSA3, LSA5) target the infective stages of the parasite following mosquito bite and our antibody-dependent anti-malaria vaccines (ADAMVAX antigens MSP3, LSA5) target the asexual or disease-causing parasite stages in the blood.
Our vaccines intend to cover the specific and unmet needs of all individuals at risk for life-threatening malaria, from populations living in malaria endemic areas to travelers or deployed employees and soldiers.
First-generation prototypes have been clinically tested and found to be safe and immunogenic in early clinical trials. In the case of MSP3, the first-generation prototype, MSP3-LSP, reduced malaria disease in children, an action associated with vaccine-induced immune responses.
Our second-generation candidates have been designed to further increase magnitude and duration of immune responses and maximize the probability of achieving high-level efficacy and clinical benefit.
All 3 candidates have the major advantage of being fully conserved in all malaria infections, which means that there is no change in the molecular target from one malaria strain to another (which is a major concern for all competitors).
Merozoite Surface Protein-3 (MSP3)
A blood stage antigen
Our most advanced candidate with clinical proof-of-concept
- Vaccination with the first-generation MSP3 vaccine, MSP3-LSP, successfully induced antibodies (against-MSP3) that killed P. falciparum parasites.
- A Phase 2b proof-of-concept trial in young children aged 1-4 years in 2 sites in Mali showed efficacy against malaria disease: protection was associated with anti-MSP3 antibodies.
- MSP3-Biofusion, the second generation product, is 20-100 fold more potent at inducing these correlates of protection.
Liver-Stage Antigen-3 (LSA3)
A Pre-erythrocytic Antigen
Fast-track clinical development through the malaria human challenge model
- Proof-of-concept studies in chimpanzees demonstrated protection against massive P. falciparum sporozoites challenges up to one year after immunization.
- Vaccination with the first-generation LSA3 vaccine, LSA3-FL, demonstrated safety in humans. The first-generation prototype induced immune responses that were found to be restricted by the presence of regulatory regions on the vaccine construct.
- A second-generation candidate has been designed to remove the identified regulatory regions.
Liver-Stage Antigen-5 (LSA5)
A Natural Combination Antigen
Highly unique molecule combining MSP3 and LSA3 advantages
- LSA5 induces protection against both pre-erythrocytic and asexual blood stages.
- Its protective role and remarkably high immunogenicity were confirmed in various in vitro and proof-of-concept studies in primates.
- Vaccination with the first-generation LSA5 vaccine, PEBS, demonstrated safety in humans. The first-generation prototype induced unsatisfactory immune responses thought to be due to inadequate adjuvantation.
By the end of their second decade of life, people living in malaria endemic areas and who are persistently exposed, since birth, to P. falciparum malaria, become clinically immune to the disease. This immunity confers the ability to control parasite loads with very low levels, and to withstand those low levels of parasitemia without developing serious clinical illness.
Vac4All's founder studied this naturally acquired immunity and demonstrated parasitological and clinical protection in P. falciparum infected Thai children who were infused with immunoglobulin from malaria-immune adult Africans (Sabchareon et al. 1991).
Comparison of non-protective to protective antibodies led to the identification of an immunological mechanism associated with the protection (Bouharoun-Tayoun et al. 1990). We called this mechanism Antibody-Dependent Cellular Inhibition (ADCI) because the protective antibodies acted with monocytes to stop parasite growth. Subtypes of antibodies that can bind to white blood cells, known also as cytophilic antibodies, play a crucial role in ADCI (Bouharoun-Tayoun et al. 1995; Bouharoun-Tayoun et al. 1991). The ADCI assay provided a biological measure of a clinically relevant effect, and an approach to malaria vaccine discovery, design, and development.
- The MSP3 parasite was discovered this way using the ADCI assay to screen the genome for targets of antibodies acting through this mechanism (Oeuvray et al. 1994).
- Observational studies have consistently found association between cytophilic anti-MSP3 IgG1 and IgG3 and a reduction in malaria risk. Studies in several exposed populations show that MSP3 induces antibody responses that are strongly associated with clinical protection against disease (Roussilhon et al. 2007, Soe et al. 2004, Fowkes et al. 2010).
- Finally, this type of protection appears to be strain-independent. We found that the region containing ADCI target epitopes was fully conserved across more than 130 P. falciparum isolates (Singh et al. 2004, Osier et al. 2007). This could prevent polymorphism and immune selection issues plaguing competing approaches.
- Vaccination with our first vaccine construct, the MSP3-LSP (long synthetic peptide) vaccine successfully induced cytophilic anti-MSP3 antibodies that killed P. falciparum parasites through ADCI in vitro and in vivo (Druilhe et al. 2005).
- A Phase 2b proof-of-concept trial in young children in Mali found that vaccination could protect a subgroup of children from malaria, and that this protection was associated with stronger cytophilic Anti-MSP3 responses.
- The results provide proof that reduction in clinical malaria can be achieved, even with a relatively simple vaccine construct and formulation, and confirm the nature of the immune responses to induce. However, the moderate efficacy seen and the limited duration of vaccine-induced immune responses have led us to design our second-generation vaccines which proved to induce greater levels of immune responses.
In addition to natural immunity, immunity to malaria can be artificially-induced through intravenous administration of healthy subjects with radiation-attenuated sporozoites. Subjects appear to be completely protected when exposed to falciparum infected mosquitoes under laboratory condition, making this a highly attractive immunity to mimic. Most current approaches have focused on the circumsporozoite antigen from the sporozoite stage, like the GSK RTSS vaccine, a "polymorphic molecule" which is not "conserved" in all parasites. In addition, our research shows that this strategy overlooks the importance of the liver stages of parasite to the induction of this type of immunity, and will unlikely lead to highly effective vaccines (Druilhe et al. 2007).
- We have shown that protection due to immunization with radiation-attenuated sporozoites (Spz) is associated with the transformation of the irradiated sporozoites into persistent growth-arrested hepatic trophozoites (Mellouk et al. 1990). Antigens expressed by these liver-stage parasites are both a target of defense mechanisms and a crucial component in inducing protective responses. Recent experiments in humans found subcutaneous inoculation of sporozoites failed to protect, supporting our finding about the importance of the intra-hepatic location (Mellouk et al. 1990).
- LSA3 was identified using sera from subjects protected against challenge versus that of unprotected subjects receiving over-irradiated parasites (Mellouk et al. 1990). LSA3, a highly-conserved protein, is expressed on the sporozoite surface and synthesized in the liver-stages, and remarkably antigenic in humans compared to other antigens. Proof-of-concept studies in chimpanzees demonstrated strain-independent protection against P. falciparum sporozoite challenges up to one year after immunization (Daubersies et al. 2000). Responses were strongly boosted on re-challenge. Although antibodies exert potent activity against sporozoite hepatocyte invasion, immunological investigations found protection associated with high antigen-specific interferon-γ activity (Perlaza et al. 2011).
- Our first-generation LSA3 prototype vaccine, a full-length recombinant protein, was found to contain numerous T-Reg epitopes components of the immune system that suppress immune responses of other cells. The results showed a downregulation of interferon-γ responses. This was in contrast to LSA3 fragment, DG729, which was the antigen used in most of the animal proof-of-concept studies, and is the antigen of the next-generation LSA3 candidate.
- The new construct has been designed to contain the epitopes that are associated with protection in the pre-clinical animal challenge studies and excludes two T-regulatory regions. This translates into markedly improved human immune responses in HIMM. Moreover, the sequence of the DG729 clone is a fully conserved region.
- LSA5 was recognized by sera from volunteers immunized with radiation-attenuated sporozoites and is unique as it induced protection against both pre-erythrocytic and asexual blood stages. The protective role of LSA5 against pre-erythrocytic stages is supported by convergent evidence from in vitro invasion inhibition studies, in vivo protection by passive transfer of anti-LSA5 antibodies, and by proof-of-concept studies in primates protected from challenge by vaccination with recombinant LSA5.
- Against the blood-stages, both naturally-occurring human and artificially-induced animal anti-Pf LSA5 antibodies exert an ADCI-mediated parasite growth-inhibition effect. Antigenicity is high in individuals from endemic areas with IgG3 antibodies predominating in individuals with premonition. A large number of epidemiological studies found strong association with protection against clinical malaria attacks and improved prognosis of drug-treated cerebral malaria. Finally, LSA5 is highly immunogenic, achieving remarkable high titers in mice and greater ADCI activity than MSP3.
While the vast majority of our competitors are seeking the “magic” adjuvant to turn a mediocre antigen into a strong immunogen, we chose a different approach which focuses on proper selection of antigens and rational design and improvement of our antigen constructs.
Our second-generation formulations have been greatly improved using innovative strategies that circumvent the common approach of using novel adjuvants that would raise the regulatory and safety bar and delay development.
Our next-generation candidates show much improved level and duration of immune responses in pre-clinical studies, something we believe will greatly improve on our first-generation results and achieve high efficacy.
Our optimization strategies include:
Adding a carrier protein to create biofusion proteins
- Ou new constructs induce much higher and longer-lasting responses than our first-generation vaccine prototypes (up to 20-100 fold higher) in animal proof-of-concept studies.
- An approach with proven added value in licences vaccines against pneumococcus and meningitis, where carrier protein conjugation leads to the magnitude and durability of vaccine responses.
- A patented manufacturing process cutting costs drastically as compared to existing procedures.
- Using an established vaccine technology from widely used licensed pediatric vaccines minimizes manufacturing, safety and regulatory risks, giving us an enormous head start over novel adjuvants or viral vectors favored by others in this field.
Tailoring vaccine constructs
- Our observations and research indicate the existence of molecular regions that down-regulate the intensity of immune responses most-likely to prevent the high responses that would otherwise eradicate the parasite.
- Identification of such regulatory regions leads us to tailor vaccine constructions and to obtain as expected a much greater immunogenicity. This avoids resorting to complex delivery systems or novel adjuvants which has the added advantage of not being dependent on external Intellectual Property.
Human Immunogenicity Mouse Model (HIMM)
- We have improved our vaccine formulations screening capabilities through the in-house development of a unique means to assess human responses at pre-clinical level, the Human Immunogenicity Mouse Model (HIMM) to overcome limitations of routine mice models.
- The model is an immune-deficient mouse transplanted with human spleen tissue to mimic human immune responses.
- Results in the HIMM replicated the observations from the LSA3-FL clinical trial and led to the identification of T-regulatory regions in this first-generation prototype.
- This parallelism indicates the model is a much more relevant screen for determining vaccine formulation, dose and schedule for clinical testing.
Science & Pipeline
We are pushing forward with the clinical development of our pipeline of second-generation candidates according to the following scheme:
Merozoite Surface Protein-3 (MSP3) Biofusion
- Phase 1/2b Clinical development up to Proof-of-Concept to be implemented within the next 2 years;
- Phase 2b success would lead to Phase 3 pivotal clinical trials with emphasis in the endemic southern regions of the world.
Liver-Stage Antigen-3 (LSA3) Biofusion
- Phase 1a to assess safety and immune responses;
- Fast-Track assessment of protection: specialized clinical trial (Phase 2a) with Infected Mosquito Challenge to assess protection.
Liver-Stage Antigen-5 (LSA5) Biofusion
- Phase 1a to assess correlates for both pre-erythrocytic and erythrocytic stages;
- Fast-Track assessment of protection: specialized clinical trial (Phase 2a) with Infected Mosquito Challenge to assess pre-erythrocytic protection;
- Proof-of-Concept Phase 2b clinical trial to assess protection against both stages.