Targeting human inducible regulatory T cells (Tr1) in patients with cancer: blocking of adenosine-prostaglandin E₂ cooperation

Abstract

Introduction: Emerging data suggest that human inducible regulatory T cells (Tr1) produce adenosine and prostaglandin E(2) and that these factors cooperate in mediating immune suppression.

Areas covered: Human Tr1 present in human tumors or blood of cancer patients express ectonucleotidases, CD39 and/or CD73, hydrolyze ATP to adenosine and are COX-2 positive. Expression of CD39 and/or CD73 on human tumors favors expansion and suppressor functions of Tr1. Adenosine and PGE(2) signal via adenosine 2A receptor (A(2A)R) and prostaglandin E(2) receptor 2 (EP(2)R) expressed on effector T (Teff) cells, suppressing their anti-tumor functions by a common mechanism involving upregulation of cytosolic cAMP levels and protein kinase A (PKA) type I activation. The frequency and activity of circulating CD4(+)CD39(+) and CD4(+)COX-2(+) Treg subsets increase in advanced disease and also following oncologic therapies.

Expert opinion: Pharmacologic blocking of adenosine-PGE(2) collaboration provides a clinically-feasible strategy for disarming of Treg. Used in conjunction with conventional anti-cancer drugs or immune interventions, pharmacologic inhibitors could improve outcome of oncologic therapies.

Figure 1

(A) Ectonucleotidase expression in PCI-13 and ANT-1 tumor cell lines. Tumor cells were surface stained for CD39 and CD73 and analyzed by flow cytometry. One representative experiment of 3 performed is shown. (B) Adenosine production by PCI-13 and ANT-1. 1×10⁶ PCI-13 and ANT-1 tumor cells were incubated with either 100μM ATP in the presence or absence of ARL67156 (250μM), an ecto-ATPase inhibitor, or 100μg AMP in the presence or absence of α,β-methylene ADP (100μM), a specific CD73 inhibitor. One representative experiment of 3 performed is shown.

Figure 2

(A) Flow cytometry of human CD4⁺ T cells showing surface expression of CD39 and CD73. (B) Confocal images of a human HNSCC sectioned and stained for CD4⁺CD25⁺CD39⁺ or CD4⁺CD25⁺CD73⁺ T cells. In panel B, CD4⁺ cells are green, CD25⁺ cells are red; in panel C, CD39⁺ cells are blue, CD4⁺CD25⁺CD39⁺ cells are violet and Tconv are red; in panel D, CD73⁺ cells are blue, CD4⁺ cells are green, CD25⁺ cells are red and CD4⁺CD25⁺CD73⁺ cells are violet. Mag × 200; inserts × 400. Reproduced with permission from the AACR Publication Department [23].

Figure 3

Tr1-derived adenosine and PGE₂ bind to A_2AR and EP2R expressed on T effector cells and suppress functions of T effector cells.

Figure 4

(A) Western blots showing expression of ectonucleotidases, CD39 or CD73, and of CD26 and ADA in human isolated CD4⁺CD25^high Treg and CD4⁺CD25^neg conventional T cells (Tconv). (B) Confocal images of Treg and Tconv showing co-expression of 26 and ADA in Tconv. Reproduced from an article originally published in J. Biological Chemistry 285:7176, 2010. ©The American Society for Biochemistry and Molecular Biology.

Figure 5

(A) The frequency of CD4⁺CD39⁺ T cells in the peripheral blood of HNSCC patients is increased compared to that in normal controls (NC). The percentages of CD39⁺ Treg were tested in HNSCC patients prior to or after oncologic therapy. (B) Tr1 cell subsets in the peripheral circulation of patients with HNSCC or normal donors (ND). The frequency of CD4⁺IL-10⁺, CD4⁺TGF-β1⁺, CD4⁺COX-2⁺ and CD4⁺CD39⁺ Treg subsets was evaluated by flow cytometry in patients with active disease prior to therapy (AD), no evident disease (NED) after chemoradiotherapy and in normal controls (NC). Figure 5A is reproduced with permission from the AACR Publication Department [23]. Figure 5B is reproduced from an article originally published in Journal of Biological Chemistry 285: 27571–80, 2010. ©The American Society for Biochemistry and Molecular Biology.