Title: Development of humoral immune responses and immunological memory against malaria vaccine-candidates in humans
PhD Student: Ajua Anthony
Supervisors: Dr. Benjamin Mordmüller (University of Tübingen, Institut für Tropenmedizin, Germany) and Dr. Michael Theisen (Statens Serum Institut, Denmark)
Collaborators: Prof. Peter G. Kremsner (University of Tübingen, Institut für Tropenmedizin, Germany) and Prof. Robert Sauerwein (Radboud University Medical Centre, the Netherlands)
Background: Transition from first-time-in-man studies in unexposed volunteers to clinical trials in exposed populations is a critical step in vaccine development. This is especially true for malaria vaccines because encounter with the pathogen starts early in life and reaches high levels in certain populations. In addition, co-infections, administration of other vaccines at the same time, and a continuous and high exposure to a variety of pathogens complicates the immunological response pattern, and affects long-term vaccination-success. So far, only very little is known about the effect of these co-variates on immune responses and B-cell memory to vaccines. Ongoing clinical trials as well as planned investigations within the European Malaria Vaccine Development Association (EMVDA) framework bear the unique possibility to do systematic side by side investigations on the same vaccines (antigens and adjuvants) in exposed and non-exposed populations in different age groups and with different vaccination schemes. The project is embedded in current and future clinical trials in Tübingen, Lambaréné, and Nijmegen. Collaboration with all other clinical trial sites is highly desirable. Our main focus is the humoral and memory B-cell response to erythrocytic asexual-stage-vaccines, but the infrastructure allows synergistic interactions with other immunologically centred projects.
Aim of the project: The projects aim is to compare the development of humoral immunity and immunological memory against different eythrocytic stage malaria vaccine-candidates in non-exposed volunteers, exposed adults, children, and infants.
Methods: Total immunoglobulin G (IgG)-, IgG-subclass-ELISA, and memory B-cell ELISPOT against vaccine-antigens represent the core-experiments. They will be performed in all study populations using the same techniques before and at different time-points after immunization. Furthermore, extended Th1/Th2 profiling with and without stimulation will be done to assess the cytokine and T-helper cell environment of B-cell maturation. These core-techniques are established, validated, and used in two current GMZ2-trials (GMZ2 is a MSP3-GLURP fusion protein). In heavily exposed populations, reactivity against vaccine-antigens is common and complicates the distinction between natural and vaccine-induced effects. Therefore the core-protocol is extended by techniques to investigate the evolution of antibody responses against recombinant as well as crude antigens, which rely on different conformations of the protein (such as ELISA, Western Blot, and immunofluorescence). Furthermore a correlate of individual memory B-cell clones will be analysed by repertoire-cloning of antibody fragments from mRNA of in-vitro generated antibody-secreting cells. Repertoire-cloning can be integrated into already established protocols for memory B-cell ELISPOT. B-cell reactivity provides an internal control for the outcome of the cloning. Additionally, subtractive hybridisation of samples obtained during the course of vaccination can give us information of the plasticity of B-cell memory over time.
Functional antibody-assays (growth inhibition with and without monocytes; GI/GIM) will be compared between different clinical settings within the consortium.
Expected outcome: We will characterise the development of circulating antibody- and B-cell memory-responses in clinical vaccine trials in Europe and Africa by complementing immunological techniques. Established and validated protocols are compared with newly developed methods. All techniques are tested as surrogate marker for efficacy. A spin-off of our work is a set of standard tools, including experimental procedures and software for ELISA, ELISPOT, and colony-counting that will be provided to the scientific community under a general public license.