Combined vaccines capable of conferring simultaneous immunity to different pathogens or diseases upon one single injection emerge as the most manageable solution to protect people. Although some combined vaccines have already been successfully developed, very little is known on the actual immunological interferences that might occur between two or more antigen specific immune responses simultaneously induced in vivo. Antigenic competition is very poorly documented in the literature as well as in clinical trial data. Understanding the mechanisms positively or negatively regulating the interactions between simultaneous antigen specific immune responses is critical for the development of efficient multivalent vaccines. We therefore propose to set up in vivo and in vitro models that will allow us to study the molecular basis of interferences between several immune responses. Formulation capable of reducing these antigenic competitions will be tested. The expertise of AVP in the field of combined vaccines is extensive and long-lived. Conducting such work in AVP research facilities is a unique opportunity that should lead to the success of this project. The following will be provided: expertise and equipment of the host research facilities, a continuous monitoring by a multi-disciplinary scientific proug and the stimulating environment of the second largest city of France which provides many opportunities of scientific interactions.