Title: Vaccine-induced and natural immune responses to AMA1 in Mali
PhD Student: Boaz Owino Owuor
Supervisors: Prof. Alan Thomas (BioMedical Primate Research Center, the Netherlands) and Prof. Ogobara Doumbo (Malaria Research and Training Centre, Mali)
Collaborators: Dr. Ed Remarque (BioMedical Primate Research Center, the Netherlands), Dr. Roma Chilengi (African Malaria Network Trust, Tanzania), Dr. Bourema Kouriba (Malaria Research and Training Centre, Mali), Dr. Daniel Dodoo (Noguchi Memorial Institute for Medical Research, Ghana), Dr. Leonie van Duivenvoorde (BioMedical Primate Research Center, the Netherlands)
Background: Apical Membrane Antigen 1 (AMA1) is a micronemal protein of apicomplexan parasites that appears to be essential during infection of host cells. Immune responses to Plasmodium AMA1 can have profound parasite inhibitory effects both as measured in vitro and in animal challenge models, suggesting AMA1 as a potential vaccine candidate, and phases I and II studies are currently ongoing. However, AMA1 is polymorphic, probably as a result of immune selection operating on an important target of naturally occurring immunity. A thorough understanding of the acquisition and maintenance of AMA1 allele-specific B and T-cell responses in naturally exposed and vaccinated subjects is pivotal for the development of an efficacious vaccine. The ultimate target group for malaria vaccines are young children, and additional information is required on the kinetics of AMA1-allele-specific responses in this group. The PhD programme will focus on the evaluation of natural and vaccine-induced immune responses to AMA1. Both humoral and cellular immunity to AMA1 will be in depth investigated in adults and children.
Aim of the project:
1. Evaluate immune responses in AMA-1 Phase Ib clinical trial (Humoral and Cellular)
2. Describe how AMA1 allele specific immunity develops with age
3. Improve understanding why memory responses to AMA1 are short-lived
4. Strengthen immunology capacity of MRTC.
Methods: Samples from the following sources will be available to the project: 1- Sera and PBMC collected in the currently ongoing AMANET-sponsored Phase Ib clinical trial with AMA1 in Bandiagara. 2- Samples collected in a Bandiagara field study in children. 3- PBMC collected at the Bamako National Center for Blood Transfusion (CNTS). 4- bone marrow samples collected at the Bamako University Hospital (BUH).
Samples collected in the phase Ib trial will yield pivotal information on AMA1 immunity in adults and the following topics will be addressed: 1- Vaccine safety and basic immunology (Elisa and IFA on vaccine Ag). 2- Allelic responses, antibody isotypes and subclasses on a broad panel of AMA1 alleles. 3- Functionality, quality and fine specificity of humoral response (GIA, Avidity and Competition Elisa). 4- T cell immunology: Lymphocyte Stimulation Tests for proliferation and cytokine production, Elispot as well as Intra Cellular Staining with emphasis on memory T cells (CD4 and CD8). 5- B cell immunology with emphasis on memory B-cells: Elispot on the vaccine antigen and FACS analysis, how long-lived are malaria-specific memory B-cells as compared to control antigens (e.g. Tetanus Toxoid and influenza)? The latter question will also be addressed in PBMC samples from the Phase Ib, the CNTS and in bone marrow samples from the BUH.
A prospective field study will be conducted in children aged 1 to 10 years. Morbidity data and blood samples will be collected before, during and at the end of the transmission season. AMA1 alleles will be typed and humoral immune responses to a broad panel of AMA1 alleles will be determined. This will yield insights on the number of circulating AMA1 alleles and the polyclonality of infections as well as on the relation between circulating alleles and AMA1 allele-specific antibody responses in children. The relation between antibody levels and clinical malaria will also be studied in this cohort. The panel of antigens for this study will be extended by the Afro Immuno Assay (AIA) antigens (viz. MSP119, MSP3 and GLURP). MRTC has recently joined AIA.
The PhD programme will be a sandwich type with half of time to be spent in Mali. The PhD will be supervised by senior BPRC and MRTC immunologists and will be embedded in the AIA programme. Both AIA and BPRC will transfer the required methodology and thereby contribute to the immunology capacity at MRTC.
Expected outcome:
1. Description of B and T-cell immune responses in AMA-1 Phase Ib clinical trial
2. Description of AMA1 allele specific immunity development with age
3. Improved understanding of memory responses to AMA1
4. Scientific rationale for improved AMA1-based vaccines
5. Strengthened immunology capacity of MRTC