Regulatory T cells — cells that maintain self-tolerance and inhibit inappropriate immune responses in vivo — come in many guises, and many diseases that are characterized by a dysregulated immune response, including asthma and autoimmunity, are associated with regulatory T-cell defects.

Two articles in this issue focus on different approaches to exploit regulatory T cells as a therapy. On page 271, Catherine Hawrylowicz and Anne O'Garra review the evidence that current therapeutic approaches for the treatment of some allergic diseases might function by inducing interleukin-10 (IL-10)-secreting regulatory T-cell populations. They also outline approaches that could be used in the future to improve the generation of allergen-specific IL-10-secreting regulatory T cells, with the aim of long-term alleviation of disease symptoms. By contrast, Jeffrey Bluestone (page 343) discusses the therapeutic potential of expanding the naturally occurring CD4+CD25+ regulatory T-cell population, either polyclonally or in an antigen-specific manner, for the treatment of graft-versus-host disease and autoimmunity. In his opinion, such treatments will soon be introduced.

Immunotherapy is also the topic of a Review by Jacques Banchereau and A. Karolina Palucka (page 296). In this article, they describe advances in our understanding of the ability of distinct dendritic cell (DC) subsets to induce different immune responses and the implications that this has for the development of DC-based vaccines against cancer. Similarly, on page 331, Michael Lotze and Kevin Tracey review the recent discovery that high-mobility group box 1 protein (HMGB1) is a cytokine with pathological effects in sepsis, arthritis and cancer, and they discuss the potential for modulation of its release and activity for the treatment of these diseases.