Prior exposure to the carrier regulates rat immune responses to a conjugate vaccine

Small vaccine antigens including peptides generally need to be linked to larger molecules or carriers in order to induce high levels of immune responses. The potential of unwanted immune responses to the carriers represents a major drawback for the conjugated vaccines. The carriers could also regulate the immune responses to the haptens and these effects need to be prevented in order to achieve adequate responses to the vaccines. We examined means to reduce the unwanted reactions to the carrier. For this purpose, we investigated whether prior exposure of rats to a human IgG(1) (hIgG(1)) carrier would affect their subsequent responses to an OVA peptide (i.e., OVA(173-196)). Prior exposure to the hIgG(1) carrier did not affect the T cell responses to the peptide antigen. However, IgG(1) Ab responses to the peptide antigen were enhanced while IgE Abs were reduced. These results show that responses to the hapten are not systematically relevant to the carrier pre-immunization and that the conjugate could achieve desired responses by selective immune responses suppression. Such models of vaccines with enhanced anti-hapten responses and reduced levels of potentially harmful responses could be of great interest for the development of new immune therapies.