The samples (n = 27) displayed an almost complete effacement of the normal LN architecture by CLL cells and evidence of morphologically distinct pseudofollicles, comprising areas rich in prolymphocytes and paraimmunoblasts. CD39 and CD73 expression patterns were investigated by immunohistochemistry in LN sections from CLL patients. The adenosinergic axis acts in a local microenvironment, where extracellular levels of ATP and ADP might be increased as a consequence of an accelerated cellular turnover. They are coexpressed on many cells, including regulatory T cells, and by the vasculature within solid tumors. 17ĬD39 and CD73 are members of a pathway of ectoenzymes that participate in a cascade leading to ADO synthesis. 15, 16 Less known are the effects mediated by the adenosinergic axis through autocrine mechanisms. 13, 14 ADO production is an integral component of the suppressive machinery of regulatory T cells, blunting effector T-cell proliferation and secretion of T-helper 1–type cytokines. 12 ADO may be taken up by cells to reconstitute the nucleotide pool, or it may elicit potent immunosuppressive and anti-inflammatory responses, mediated through the interaction with a specific family of type 1 purinergic G protein-coupled receptors (A1, A2A, A2B, and A3). As examples, CD39 (ENTPD1, EC 3.6.1.5) hydrolyses ATP or ADP to AMP AMP is then rapidly degraded to ADO by soluble or membrane-bound CD73 (5′-nucleotidase, EC 3.1.3.5). Nucleotides also may serve as substrates for the ectonucleotidases that are surface molecules with catalytic sites located in the extracellular compartment. 9 Extracellular ATP binds multiple type-2 purinergic and pyrimidinergic (P2Y and P2X) receptors, influencing cellular metabolism, migration, proliferation, and apoptosis (reviewed in Burnstock 10 and Burnstock and Verkhratsky 11). These data are consistent with the existence of an autocrine adenosinergic loop, and support engraftment of leukemic cells in growth-favorable niches, while simultaneously protecting from the action of chemotherapeutic agents.Įxtracellular nucleotides and nucleosides, such as adenosine triphosphate (ATP) and adenosine (ADO), respectively, may participate in creating favorable conditions that promote tumor growth and survival, while suppressing the host immune responses. Activation of the ADO receptors increases cytoplasmic cAMP levels, inhibiting chemotaxis and limiting spontaneous drug-induced apoptosis of CLL cells.

CD73-generated extracellular ADO activates type 1 purinergic A2A receptors that are constitutively expressed by CLL cells and that are further elevated in proliferating neoplastic cells. In peripheral blood, CD73 expression occurs in 97/299 (32%) CLL patients and pairs with CD38 and ZAP-70 expression. CD39 +/CD73 + CLL cells generate ADO from ADP in a time- and concentration-dependent manner. CD73 expression is highest on Ki-67 + CLL cells, adjacent to T lymphocytes, and is further localized to perivascular areas. By immunohistochemistry, CD39 is widely expressed in CLL lymph nodes, whereas CD73 is restricted to proliferation centers. We have tested whether the expression of CD39 and CD73 by chronic lymphocytic leukemia (CLL) cells activates an adenosinergic axis affecting growth and survival. Extracellular adenosine (ADO), generated from ATP or ADP through the concerted action of the ectoenzymes CD39 and CD73, elicits autocrine and paracrine effects mediated by type 1 purinergic receptors.

Snapgene confocal microscopy