The tumor microenvironment impairs CLL response to the exit signal from lymphoid tissues, sphingosine 1-phospate (S1P)

BORGE MERCEDES; REMES LENICOV FEDERICO; NANNINI PAULA; DE LOS RÍOS ALICANDÚ MERCEDES; FERNÁNDEZ GRECCO HORACIO; BEZARES FERNANDO; MORANDE PABLO; OPPEZZO PABLO; GIORDANO MIRTA; GAMBERALE ROMINA

Cologne

Workshop; FIFTEENTH INTERNATIONAL WORKSHOP ON CHRONIC LYMPHOCYTIC LEUKAEMIA; 2013

The leukemic clone of CLL patients is characterized by a subtle balance between cells circulating inthe blood and cells located in permissive niches in lymphoid organs, where CLL cells are activatedand proliferate in close contact with stromal cells, nurse like cells (NLC) and activated T cells. Whilenumerous reports have studied the mechanisms involved in CLL entry to lymphoid tissues, there isscarce information regarding the mechanisms involved in the leukemic clone exit from this permissiveniche to circulation. Sphingosine-1 phosphate (S1P) is a bioactive sphingolipid which exerts most ofits function as a specific ligand for a family of five G-protein-coupled receptors, S1PR1 being the mainreceptor involved in lymphocyte exit from lymphoid tissues. Our central hypothesis assumes that, byacting through S1PR1, S1P regulates the egress of the leukemic clone from lymphoid tissues toperipheral blood, a process that may be delayed by activatory signals delivered by the tumormicroenvironment. To test our hypotheses we aimed to determine whether key signals from themicroenvironment reduce the migratory response towards S1P. Thus, purified CLL cells were culturedwith different stimuli, such as CXCL12, fibroblast CD40L+ and antibodies anti-IgM, in order to induceBCR crosslinking. Then, the in vitro chemotaxis assay towards S1P was performed by employing thetranswell system. We found that CXCL12 and the crosslinking of CD40 or surface IgM significantlyreduce the migratory response towards S1P (Fig. 1 A) and diminish the expression of S1PR1evaluated by qPCR (Fig. 1 B) and flow cytometry (Fig. 1 C). Similarly, co-cultures with autologousNLC, which represent an accurate model for the microenvironment in secondary lymphatic tissues,reduced the migratory response towards S1P (Fig. 1 D) and the expression of S1PR1 (Fig. 1 E andF).In conclusion, our data show that the supportive microenvironment reduce the expression of S1PR1and the in vitro chemotaxis assay towards S1P. Altogether, these results suggest that the activationwithin lymphoid tissues may reduce the in vivo exit of CLL cells to circulation, extending the dwell timeof the leukemic clone in the tissues that favor their accumulation. A better understanding of the role ofS1P in CLL will contribute to the current knowledge of leukemic cell biology, will provide insights intothe progression of the disease andmight help to find potential targetsfor novel therapeutic treatments.