Splenic Marginal Zone Granulocytes Acquire an Accentuated Neutrophil B-Cell Helper Phenotype in Chronic Lymphocytic Leukemia

Abstract

Recruitment of tumor-associated macrophages and neutrophils (TAM and TAN) to solid tumors contributes to immunosuppression in the tumor microenvironment; however, their contributions to lymphoid neoplasms are less clear. In human chronic lymphocytic leukemia (CLL), tumor B cells lodge in lymph nodes where interactions with the microenvironment occur. Tumor cell homing stimulates proliferation, such that engagement of the B-cell receptor is important for malignant progression. In the Em-Tcl1 murine model of CLL, we identified gene expression signatures indicative of a skewed polarization in the phenotype of monocytes and neutrophils. Selective ablation of either of these cell populations in mice delayed leukemia growth. Despite tumor infiltration of these immune cells, a systemic inflammation was not detected. Notably, in progressive CLL, splenic neutrophils were observed to differentiate toward a B-cell helper phenotype, a process promoted by the induction of leukemia-associated IL10 and TGFb. Our results suggest that targeting aberrant neutrophil differentiation and restoring myeloid cell homeostasis could limit the formation of survival niches for CLL cells. Cancer Res; 76(18); 5253-65. Ó2016 AACR.

Chronic lymphocytic leukemia cells increase neutrophils survival and promote their differentiation into CD16highCD62Ldim immunosuppressive subset

“…Although we did not observe a BAFF or APRIL differential expression between circulating neutrophils from HD and CLL patients, it is conceivable that, once in the lymphoid tissues, reprogrammed CD16 high CD62L dim cells receive additional signals from the microenvironment to promote leukemic B cell survival. This hypothesis is supported by a previous report in the Eμ‐TCL1 murine model of CLL that exhibited an expanded neutrophil population with B‐helper properties in the spleen of leukemic mice which does not exist in the bone marrow, suggesting that the local environment is critical for shaping the gene expression program of B helper neutrophils.…”

“…e). Given that longer lifespan of TANs has been associated with increased expression of Bfl‐1, an antiapoptotic member of the Bcl‐2 family, we evaluated Bfl‐1 expression on HD‐neutrophils exposed to CM. By Western blot, we found that Bfl‐1 levels were significantly upregulated in HD‐neutrophils incubated for 18 hr in CM compared to those incubated in control medium (Fig.…”

“…Previous reports indicate that CLL cells were capable of modulating immune cell functions turning them into an immunosuppressive/tumor‐supportive phenotype. Although almost every cell type in lymphoid tissues can be modified by the leukemic clone, myeloid cells are crucial to promote its progression as shown in the Eμ‐TCL1 mouse model of CLL . In this model, it was shown that spleen marginal zone neutrophils in contact with CLL cells had a longer lifespan and acquired a tumor‐supportive phenotype .…”

The splenic marginal zone shapes the phenotype of leukemia B cells and facilitates their niche-specific retention and survival

“…with 1 mg/kg body weight FTY720 (Cayman Chemical), a S1P 1 , S1P 3 , S1P 4 , and S1P 5 agonist. Three hours later mice were killed and peripheral blood and spleens were further analyzed by flow cytometry and immunohistology.…”

“…2 In CLL, tumor cells interact with a variety of different stromal cells, such as mesenchymal stromal cells, monocytederived nurse-like cells, and also with T lymphocytes and myeloid cells. 3,4 Employing the murine Em-Tcl1 transgenic model of CLL, we recently demonstrated that malignant B cells home to the B cell follicle, where they find a growth-promoting microenvironment in close proximity to the follicular dendritic cell network (FDC). FDCs secrete CXCL13, the ligand for the chemokine receptor CXCR5, and the CXCL13/CXCR5 signaling axis mediates the recruitment of leukemic cells toward follicular FDCs.…”