Stromal Tumor Microenvironment in Chronic Lymphocytic Leukemia: Regulation of Leukemic Progression

Abstract

Chronic Lymphocytic Leukemia (CLL), the most prevalent adult leukemia in western countries, which is highly heterogeneous with a very variable clinical outcome. Emerging evidence indicates that the stromal tumor microenvironment (STME) and stromal associated genes (SAG) play important roles in the pathogenesis and progression of CLL. However, the precise mechanisms by which STME and SAG are involved in this process remain unknown. In an attempt to explore the role of STME in this process, we examined the expression levels of stromal associated genes using gene expression profiling (GEP) of CLL cells from lymph nodes (LN) (n=15), bone marrow (BM) (n=18), and peripheral blood (PB) (n=20). Interestingly, LUM, MMP9, MYLK, ITGA9, CAV1, CAV2, FBN1, PARVA, CALD1, ITGB5 and EHD2 were found to be overexpressed while ITGB2, DLC1 and ITGA6 were under expressed in LN-CLL compared to BM-CLL and PB-CLL. This is suggestive of a role for LN-mediated TME in CLL cell survival/progression. Among these genes, expression of MYLK, CAV1 and CAV2 correlated with clinical outcome as determined by time to first treatment. Together, our studies show that members of the stromal signature, particularly in the CLL cells from lymph nodes, regulate CLL cell survival and proliferation and thus leukemic progression.