Integrative profiling of follicular lymphoma at diagnosis and relapse

Follicular lymphoma (FL) is incurable with conventional therapies and has a clinical course typified by multiple relapses after therapy. These tumors are genetically characterized by B-cell leukemia/lymphoma 2 (BCL2) translocation and mutation of genes involved in chromatin modification. By analyzing purified tumor cells, we identified additional novel recurrently mutated genes and confirmed mutations of one or more chromatin modifier genes within 96% of FL tumors and two or more in 76% of tumors. We defined the hierarchy of somatic mutations arising during tumor evolution by analyzing the phylogenetic relationship of somatic mutations across the coding genomes of 59 sequentially acquired biopsies from 22 patients. Among all somatically mutated genes, CREBBP mutations were most significantly enriched within the earliest inferable progenitor. These mutations were associated with a signature of decreased antigen presentation characterized by reduced transcript and protein abundance of MHC class II on tumor B cells, in line with the role of CREBBP in promoting class II transactivator (CIITA)-dependent transcriptional activation of these genes. CREBBP mutant B cells stimulated less proliferation of T cells in vitro compared with wild-type B cells from the same tumor. Transcriptional signatures of tumor-infiltrating T cells were indicative of reduced proliferation, and this corresponded to decreased frequencies of tumor-infiltrating CD4 helper T cells and CD8 memory cytotoxic T cells. These observations therefore implicate CREBBP mutation as an early event in FL evolution that contributes to immune evasion via decreased antigen presentation. [copy number] B-cells were purified from cyropreserved tumor cell suspensions by FACS, DNA isolated, and interogated using Affymetrix 250K Nsp SNP microarrays. Aim: To track the evolution of genetic alterations during progression of follicular lymphoma. One array per tumor. [gene expression] Gene expression profiling of purified B and T cells from follicular lymphoma tumors at diagnosis and relapse Tumor B-cells (CD19+CD20+CD10+) and tumor-infiltrating T-cells (CD5+CD19-) were sorted from cryopreserved follicular lymphoma biopsies by fluorescence activated cell sorting. DNA and RNA were isolated using Qiagen AllPrep kits, and RNA was interrogated using Affymetrix U133plus2 gene expression microarray.