Memory immune response: a major challenge in vaccination.

Abstract A crucial challenge for vaccine development is to design vaccines that induce a long-lasting protective immune response, i.e., immune memory. The persistence of antigen-specific antibody titers over a protective threshold, and the ability to exibit a 'recall response' to a subsequent encounter with an antigen have long been the only measurable correlates of vaccine take and immune memory development, suffering from the disadvantage of relying on long-term monitoring of the immune response. In the last few years, advances in the technologies for the identification and characterization of the cell subsets and molecular pathways involved in the immune response to vaccination have allowed innovative approaches to the identification of early correlates of immune memory. In this review, we discuss recent data and hypotheses on early correlates of the development of immune memory, with special emphasis on the gene expression signatures that underlie the self-renewal ability of some lymphocyte subsets, and their similarities with gene expression signatures in stem cells.