The CD39/CD73 axis is a potent intrinsic repressor of T cell functionality. CAR T cell activation triggers the increase of CD39; its downregulation reduced extracellular ATP degradation and enhanced the functional capacities in CD39low CAR T cells compared with conventional CAR T cells with respect to an increase in granzyme/perforin and degranulation upon repetitive CAR stimulation. CD39low CAR T cells, moreover, displayed superior mitochondrial function and enhanced glycolytic activities. Consequently, CD39low CAR T cells outperformed conventional CAR T cells in controlling CEA+ gastric carcinoma in xeno-transplanted NSG mice. The CD39 effect is unique, since downtuning CD38, also involved in the regulation of exhaustion, did not provide benefits under stimulatory “stress conditions”. Activation-induced upregulation of CD39/CD73 contributes to a negative feedback loop for CAR T cells; downregulated CD39 levels augmented T cell anti-tumor activities by reducing AMP and adenosine-mediated repression. In the broader context, CD39 downregulation is unlikely to be sufficient as a standalone intervention in all settings but may be particularly valuable as part of combination strategies with complementary approaches targeting additional metabolic or immune checkpoint pathways to further enhance CAR T cell persistence and anti-tumor activity.