Clinical Heterogeneity of CLL: Role for Immune Dysregulation Mediated by the Lymph Node Microenvironment.

Abstract 1243

Poster Board I-265

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia and is clinically very heterogeneous. Following diagnosis, some patients do not require treatment for several years whereas others have a more aggressive disease thus requiring immediate treatment. Understanding the molecular basis of clinical heterogeneity in CLL will enhance our ability to treat this presently incurable disease effectively. CLL cells in the patient body proliferate/survive for a long time resulting in their accumulation in bone marrow (BM), lymph nodes (LN), and blood (PB). However, CLL cells do not survive for a long time once they are removed from the body, suggesting that an in vivo microenvironment provides essential proliferation/survival signals to CLL cells. Therefore, to elucidate the precise role of microenvironments on the CLL cell proliferation/survival and migration, in this study, we have analyzed CLL cells from PB (n=20), BM (n=18), and LN (n=15) from patients for their gene expression profiles using microarray. Differentially expressed genes and their associated cellular pathways were identified using significant analysis of microarray (SAM) and gene set enrichment analyses (GSEA). Among the six pathways/gene expression signatures identified (BCR-, BAFF/April-, NFκB-, PI3K/Akt, cytokine-, and tolerogenic) the most significant pathways in CLL biology are the BCR-, NFκB-, PI3K/Akt pathways and tolerogenic signature associated genes with immune dysregulation particularly with CLL cells from LN. We have already reported the differential expression of CLL cell proliferation and survival related genes belonging to BCR and NFαB pathways (Mittal et al, 2008 Blood-ASH Annual Meeting Abstract 546, page 112). In this report we have focused on differentially expressed genes associated with the tolerogenic signature and PI3K/Akt pathway. Among the eighty-three differentially expressed genes in the tolerogenic signature, based on their known role in immune regulation and/or level of significant expression comparing CLL cells from PB or BM, a few selected genes were further studied to understand their possible role in clinical heterogeneity of CLL. These genes are: CAV1, CD47, CCNB2, IL2Rαa, FOXP3, ZWINT, TGFβR1, IL22, IL10Rαa, INDO, APC, and STAT1. There was a significant increase in the expression of CD47, IL-10Rαa, CAV1, APC, CCNB2, and STAT1 in the LN cells from CLL patients; whereas the expression of IL-22R was decreased in the LN cells. These genes have been shown to be associated with immunosuppression indicating a lack of immune response against CLL in the lymph node. In addition, MAPK pathway associated genes are known to increase the survival/proliferation of tumor cells, including CLL cells. Specifically, genes associated with PI3K/Akt pathway, a part of MAPK pathways are also overexpressed in CLL cells from LN that includes AKT, 4E-BP1, PSMC4 and PDK1 genes indicating the importance of PI3K/Akt pathway in proliferation/survival of CLL cells in LN microenvironment. Based on these results, we hypothesize that differentially expressed genes belonging to the tolerogenic signature in LN of CLL patients down regulate the immune response against CLL, thus leading to enhanced disease progression whereas, overexpressed proliferation/survival-related genes belong to PI3K/Akt pathway promote proliferation/survival of CLL cells. (This work was supported by the CLL Foundation, Houston, TX and National Institutes of Health, Bethesda, MD, INBRE Grant # P20 RR016469).