We report a method of inducing antigen production in dendritic cells by in vivo targeting with lentiviral vectors that specifically bind to the dendritic cell–surface protein DC-SIGN. To target dendritic cells, we enveloped the lentivector with a viral glycoprotein from Sindbis virus engineered to be DC-SIGN–specific. In vitro, this lentivector specifically transduced dendritic cells and induced dendritic cell maturation. A high frequency (up to 12%) of ovalbumin (OVA)-specific CD8⁺ T cells and a significant antibody response were observed 2 weeks after injection of a targeted lentiviral vector encoding an OVA transgene into naive mice. This approach also protected against the growth of OVA-expressing E.G7 tumors and induced regression of established tumors. Thus, lentiviral vectors targeting dendritic cells provide a simple method of producing effective immunity and may provide an alternative route for immunization with protein antigens.