However, the effect of CD26/DPP4-deficiency or inhibition in hematopoietic cells on the regulation of blood glucose levels during an immune response to infections as well as in the context of autoimmunity or T-cell activating or chimeric antigen receptor (CAR) T-cell-based immunotherapies of cancer malignancies has not been addressed yet. The gene discussed is DPP4; the disease is cancer.