The range of regulatory T cell (T_R cell) types that control immune responses is poorly understood. We describe here a population of T_R cells that developed in vivo from naive CD4⁺CD25⁻ T cells during a T helper type 1 (T_H1)–polarized response, distinct from CD25⁺ T_R cells. These antigen-specific T_R cells were induced by CD8α⁺ DCs, produced both interleukin 10 and interferon-γ, and potently inhibited the development of airway hyper-reactivity. These T_R cells expressed the transcription factors Foxp3 and T-bet, indicating that these T_R cells are related to T_H1 cells. Thus, adaptive T_R cells are heterogeneous and comprise T_H1-like T_R cells as well as previously described T_H2-like T_R cells, which express Foxp3 and are induced during the development of respiratory tolerance by CD8α⁻ DCs.