The concept and advantages of T cells with synthetic antigen-specific T cell receptors (CAR-T cells) are well known in the art and have become a focus of pharmaceutical research and development in recent years. CAR T cells are therapeutically used in individual medicine for the treatment of cancers such as acute lymphoblastic leukemia and B cell lymphomas. However, the success of these therapies has not yet extended to solid tumors. Solid tumors pose a therapeutic challenge as they generate an immunosuppressive milieu that limits the survival and functionality of immune cells. Therefore, key features which could enable the successful treatment of solid tumors, would be improving the survival and functionality of CAR T cells in the tumor microenvironment.

The invention is to use a new combination of supplements to stimulate isolated T cells from a patient. T cells or prepared CAR T cells are incubated in a medium comprising the supplements of anti-TCRβ, anti-CD28, IL-2 and an additional inventive cocktail of cytokines. This combination not only leaves an individual activation profile on the cells which can be detected using standard technical methods, but also provides a suitable stimulus for improving the expansion, persistence, and functionality of the cells for tumor therapy, in particular of solid tumors.