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Splenic microenvironment is important in the survival and growth of Chronic Lymphocytic Leukemia in mice

Chronic Lymphocytic Leukemia (CLL), the most common adult leukemia in the western world, is characterized by accumulation of clonally expanded CD5 + CD19 + B lymphocytes in the peripheral blood and secondary lymphoid organs. CLL cell survival is dependent on B cell receptor signaling and cross-talk within the leukemia microenvironment. CLL presents with enlargement of the spleen, and lymph nodes due to accumulation of long-lived lymphocytes with impaired apoptotic mechanisms. The Eμ-Tcl1 mice, with a B cell specific overexpression of the oncogene, T cell Leukemia 1 (Tcl1), serve as an excellent model to study CLL as they develop a CLL like disease by 9–13 months of age. They exhibit splenomegaly, enlarged lymph nodes and a high peripheral blood white count. Adoptive transfer of primary CD5 + CD19 + CLL cells from the Eμ-Tcl1 mice into syngeneic recipients leads to rapid disease development. Ultrasonography of recipient mice showed a dramatic enlargement of the spleen, which preceded detection of CLL cells in the blood. Unlike various genetic modifications, which can only delay the onset of CLL, splenectomy in these models, cures or significantly delays disease development from 30–35 days to 250–270 days. Interestingly, splenectomy did not delay CLL development as significantly in animals deficient for prostate apoptotic response-4 (Par-4) compared to C57BL/6 wild type mice. Par-4 is a known tumor suppressor protein that can be secreted and induce apoptosis selectively in cancer cells but not in normal cells. Par-4 appears to regulate a specific microenvironment required for CLL growth. Presently we are investigating the role of Par-4 in the microenvironment and the cell types that are critical for CLL growth within the splenic niche.