Treg-expressed CTLA-4 depletes CD80/CD86 by trogocytosis, releasing free PD-L1 on antigen-presenting cells

Significance Immunosuppressive Tregs constitutively express CTLA-4, an immune checkpoint receptor. Addressing the role of CTLA-4 in Treg-suppressive function, we show that Treg-expressed CTLA-4, even in the absence of its cytoplasmic portion, promoted the conjugation of Tregs and antigen-presenting cells (APCs), leading to CTLA-4–dependent trogocytosis of CD80/CD86 and concomitant transfer of membrane fragments from APCs to the Treg cell surface. The depletion or blockade of CD80 by trogocytosis or solubilized CTLA-4, respectively, increased free PD-L1 by disrupting cis-CD80/PD-L1 heterodimers on APCs. Thus, Tregs can exert dual suppressive effects through the limitation of CD80/CD86 and up-regulation of free PD-L1 on APCs. Cancer immunotherapy with anti–CTLA-4 and anti–PD-1/PD-L1 blocking antibodies may enhance tumor immunity by hindering this Treg-mediated immune suppression.