Significance Regressions of some blood cancer can follow infusion of patients’ own T cells gene-modified to express a chimeric antigen receptor (CAR). These regressions are associated with extensive proliferation and engraftment of CAR T cells. However, for most common solid cancers, CAR T cells encounter antigen in a microenvironment that is immunosuppressive and lacking T cell support, and significant engraftment does not always occur. Here, we deliver enterotoxins or bispecific antibody to provide CAR T cells with support signals from antigen-presenting cells in lymphoid tissue, away from the tumor microenvironment. We demonstrate that this enables CAR T cell activation and proliferation, leading to enhanced responses against solid tumors in mice. This approach could lead to effective treatments for many common cancers.