The production of CD73-derived adenosine (Ado) by Tregs has been proposed as a resistance mechanism to anti-PD-1 therapy in murine tumor models. We reported that human Tregs express the ectonucleotidase CD39, which generates AMP from ATP, but do not express the AMPase CD73. In contrast, CD73 defined a subset of effector CD4 T cells (Teffs) enriched in polyfunctional Th1.17 cells characterized by expression of CXCR3, CCR6, and MDR1, and production of IL17A/IFNγ/IL22/GM-CSF. CD39 Tregs selectively targeted CD73 Teffs through cooperative degradation of ATP into Ado inhibiting and restricting the ability of CD73 Teffs to secrete IL17A. CD73 Teffs infiltrating breast and ovarian tumors were functionally blunted by Tregs expressing upregulated levels of CD39 and ATPase activity. Moreover, tumor-infiltrating CD73 Teffs failed to express inhibitory immune checkpoints, suggesting that CD73 might be selected under pressure from immune checkpoint blockade therapy and thus may represent a nonredundant target for restoring antitumor immunity. Polyfunctional CD73 T-cell effectors lacking other immune checkpoints are selectively targeted by CD39 overexpressing Tregs that dominate the breast tumor environment. .