OBJECTIVES: CAR-based immunotherapies represent a potentially curative strategy for hematological malignancies. However, there are a number of intracellular antigens that CAR-T cells are unable to target. Furthermore, CAR-T cells often suffer from insufficient expansion in part because of the immunosuppressive mechanisms. Lenalidomide (LEN), an immunomodulatory drug, can potentiate T cell functionality. Therefore, it is necessary to investigate combinatorial therapy using CAR-T cells and LEN for enhancing function. METHODS: We redirected T cells to express HLA-A*2402-restricted-CAR capable of recognizing WT1 peptide and adoptively transferred them into tumor-bearing mice to test their anti-tumor activity. Then we assessed the combinatorial efficacy using CAR-T cells and LEN in vitro and in vivo. RESULTS: Using an anti-WT1 CAR-T, we showed that LEN enhances CAR-T cell function in a concentration-dependent manner. Our data demonstrated that LEN improved the anti-tumor activity of CAR-T cells in vivo by increasing the infiltration of tumors with CD3 and CD8 T cells. Proteomics studies supported LEN enhanced the efficacy of CAR-T cells, including T-cell activation, mitochondrial activity and immune synapse formation. CONCLUSION: These results demonstrate that lenalidomide potentiates WT1 CAR-T activity and paves the way to evaluate the combination of LEN with CAR-T for a planned clinical trial.