P.vivax, PvDBPII
Candidate Malaria Vaccine: PvDBPII formulated with Adjuvant GLA-SE
Route of administration: Intramuscular
Development Phase: Clinical testing (Phase I, first-in-man)
Objective: To develop a blood-stage vaccine for P.vivax malaria based on recombinant PvDBPII that can induce antibodies capable of blocking parasite's entry into human red blood cells, and thus prevent or reduce clinical disease.
Current Status: Based on laboratory and immune-epidemiological data, PvDBPII has been validated as an important vaccine candidate for control of P.vivax malaria. cGMP-grade material has been produced for toxicology and clinical studies. Process for PvDBPII vaccine formulation using a stable oil-in-water emulsion (SE) containing the immunological adjuvant Glucopyranosyl Lipid A (GLA) have been optimized for preclinical and clinical development. The acute and repeat dose toxicity studies have shown this formulation to be safe and immunogenic. Based on these encouraging results, approval has been granted by the Indian regulatory authorities to test PvDBPII/GLA-SE bedside formulation in a Phase I, dose escalating clinical trial in healthy volunteers. Currently, the Phase I testing of PvDBPII/GLA-SE in 36 healthy volunteers is underway at the Human Pharmacology Unit of Syngene International Limited through three immunizations. Safety assessments and follow-up of subjects for 6 months will be conducted and the identified Immunogenicity assays will be performed.
Platform: PvDBPII represents a conserved, ~39 kDa cysteine rich region (Region II), the binding domain of Plasmodium vivax Duffy Binding Protein (PvDBP). PvDBPII antigen is based on the Salvador I (Sal I) strain of P.vivax. The recombinant antigen PvDBPII is produced in E.coli as inclusion bodies, refolded to correct confirmation and purified as ~39 kDa monomeric, functionally active protein.
Biological Rationale: The human malaria parasite P.vivax invades human red blood cells mediated by binding of its Duffy Binding Protein (PvDBP) to the erythrocyte receptor, the Duffy blood group antigen (also known as Duffy Antigen Receptor for Chemokines - DARC).
A conserved, -39 kDa cysteine rich Region II (termed PvDBPII), within the ~140 kDa PvDBP sequence, is the critical domain necessary for mediating binding to the N-terminal region of DARC on RBCs. Importantly, this pair of molecular interaction constitutes a key pathway by which P.vivax invades the host RBCs, as individuals who lack Duffy antigen on their erythrocytes are resistant to vivax infection. Thus, blocking this functionally important component of the parasite's invasion machinery offers a potential mechanism to prevent clinical malaria.
Antibodies are considered to be an important component of naturally acquired immunity against malaria. Antibodies elicited against Duffy Binding Protein targeting the PvDBP-DARC interaction have the potential to block parasite entry into the erythrocytes, and thus can prevent or reduce clinical disease.
Rationale for developing a vaccine for P.vivax malaria based on Duffy Binding Protein is supported by a number of key observations:
Antibodies raised against recombinant region II of P.knowlesi DBPa (which is a homologue of PvDBPII) effectively inhibit invasion of human erythrocytes by P. knowlesimerozoites in culture. This experiment suggested that antibodies raised against PvDBPII would inhibit receptor-ligand interaction and prevent P.vivax entry into erythrocytes. In addition, disruption of the P. knowlesi DBPa gene prevents the parasite from junction formation and abolishes invasion of human RBCs. This experiment confirmed that the Duffy Binding Protein is essential for the tight junction formation which is a pre-requisite for subsequent successful invasion.
Antibodies raised against recombinant PvDBPII in experimental animals are able to effectively block binding of PvDBPII to DARC in an in vitro functional binding assay.
An analysis of sera from residents in Papua New Guinea (a P.vivax-endemic region) proved that binding inhibitory antibodies against Duffy Binding Protein are an important correlate of protection against P.vivax blood-stage infection. Individuals with high level of PvDBP blocking antibodies, but not those with low levels, were protected from blood-stage Vivax infection. Since level of anti-DBP blocking antibodies elicited in experimental animals has been found to be many folds higher than the level observed in partially protected individuals, it is expected that vaccine-induced antibody responses would provide a better protective effect than that provided by naturally acquired immunity.
Further, high level of binding inhibitory antibodies is found to be strain-transcending that block binding of diverse PvDBPII domains to DARC. Despite polymorphic variations, the active binding site of Duffy Binding Protein was found functionally conserved across common vivax isolates (including SalI). This is an added advantage for vaccine development, since a vaccine based on SalI sequence can have a broad variant coverage.
PvDBPII project received funding from PATH, Malaria Vaccine Initiative, the Department of Biotechnology (DBT), Government of India and Biotechnology Industry Research Assistance Council (BIRAC).
Key Organizations
| Organization | Role |
| PATH, Malaria Vaccine Initiative | Funded the cGMP manufacturing |
| International Centre for Genetic Engineering and Biotechnology, New-Delhi, India | Discovered the candidate vaccine |
| Syngene International Limited, Bengaluru, India | cGMP manufacture of PvDBPII; Clinical testing (Phase I) |
| Infectious Disease research Institute (IDRI), Washington, USA | Manufacturer of adjuvant GLA SE |
| Multi Vaccines Development Program, New Delhi, India | Overall management of the Technology Transfer for cGMP Manufacturing of PvDBPII, toxicity studiesand Phase I clinical trial, validation of Immune assays |
| Gennova | PvDBPII-GLA-SE stability studies |
| Gennova | Supplied adjuvant GLA SE for Phase I clinical trial |
| Biotechnology Industry Research Assistance Council. | Funding for toxicology studies and Phase I clinical trial |