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A major challenge for immunologists has been the development of vaccines designed to emphasize cellular immune responses. One particularly promising approach is the prime–boost strategy, which has been shown to generate high levels of T-cell memory in animal models. Recently, several papers have highlighted the power of prime–boost strategies in eliciting protective cellular immunity to a variety of pathogens and have demonstrated efficacy in humans. Coupled with recent advances in our understanding of the mechanisms underlying the generation, maintenance and recall of T-cell memory, the field is poised to make tremendous progress. This Review discusses the impact of these recent developments on the future of prime–boost vaccine strategies. [Copyright &y& Elsevier]

The entry of exogenous antigen into the MHC class I-restricted crosspresentation pathway can contribute to CD8+ T cell tolerance and immunity, in particular to peripheral self-antigens or selected viruses and bacteria showing restricted tissue tropism. Dendritic cells are the key crosspresenting cells and, as such, they are thought to carry specialized machinery dedicated to this purpose. Two recent papers describe intracellular components tailored to the dendritic cell crosspresentation pathway. [Copyright &y& Elsevier]

CD8 T-cell immunity is thought to require helper activity derived from CD4 T cells. Nevertheless, under some circumstances, effective CD8-dependent T-cell responses occur in vivo without CD4 T-cell help. Several recent papers help to explain this paradox and lead to a refined view concerning the role of T helper cells and interleukin-2 receptor signaling in the production of cytotoxic T lymphocytes. [ABSTRACT FROM AUTHOR]

A recent paper on immunity and tolerance to antigenic determinants on antibody variable-regions (idiotypes) brings back to light the potential of idiotypic interactions among antibodies, B cells and T cells in the regulation of specific immune activities. The functional significance of idiotypic regulation has been established in a variety of systems, both concerning the establishment of ‘pre-immune’ diversity repertoires as well as the clonal regulation of immune responses to foreign and self-antigens. Also, recently the requirement for ‘dominant’ regulatory mechanisms in natural tolerance has received increasing support. It might thus be fruitful to evaluate the possibility that an idiotypic network has a fundamental role in the operation of the regulatory T cells that establish and maintain self-tolerance. [Copyright &y& Elsevier]