Human Vα24⁺Vβ11⁺ natural killer T (NKT) cells are a distinct CD1d-restricted lymphoid subset specifically and potently activated by α-galactosylceramide (α-GalCer) (KRN7000) presented by CD1d on antigen-presenting cells. Preclinical models show that activation of Vα24⁺Vβ11⁺ NKT cells induces effective antitumor immune responses and potentially important secondary immune effects, including activation of conventional T cells and NK cells. We describe the first clinical trial of cancer immune therapy with α-GalCer–pulsed CD1d-expressing dendritic cells. The results show that this therapy has substantial, rapid, and highly reproducible specific effects on Vα24⁺Vβ11⁺ NKT cells and provide the first human in vivo evidence that Vα24⁺Vβ11⁺ NKT cell stimulation leads to activation of both innate and acquired immunity, resulting in modulation of NK, T-, and B-cell numbers and increased serum interferon-γ. We present the first clinical evidence that Vα24⁺Vβ11⁺ NKT cell memory produces faster, more vigorous secondary immune responses by innate and acquired immunity upon restimulation.