The invention relates to mesenchymal stem cells (MSCs) for use in the treatment of a tumor, wherein said treatment comprises the combined administration of said mesenchymal stem cells with an anti-tumor immunotherapy, and wherein said MSCs do not comprise exogenous nucleic acids that encode immune response-stimulating cytokines. In a preferred embodiment the invention relates to the use of said MSCs in the treatment of a tumor and/or malignant disease, wherein the anti-tumor immunotherapy for combined administration comprises the administration of a cellular immunotherapy, preferably chimeric antigen receptor (CAR) T cells, wherein said T cell receptor binds specifically to a tumor-associated antigen, and the mesenchymal stem cells are not genetically modified.
