in vivoin vivoThe present invention generally embraces the treatment of diseases by targeting cells expressing an antigen on the cell surface. In particular the invention relates to a method for stimulating priming and/or expanding T cells genetically modified to express a chimeric antigen receptor (CAR) targeted to an antigen comprising contacting the T cells with the antigen or a variant thereof . In one embodiment the antigen or variant thereof is provided by administering a nucleic acid encoding the antigen or variant thereof.