Distinct Expression Patterns of microRNAs in Activated B Cell (ABC) and Germinal Center B (GC) Subtypes of Diffuse Large B Cell Lymphoma (DLBLC).

The Micro RNAs (miRNAs) are small non-coding, single-stranded RNAs that regulate the expression of genes by hybridizing the mRNA target with complementary sequences that are followed by translational repression, mRNa cleavage or destabilization. There is evidence that miRNA play an important role in carcinogenesis. Aberrant miRNA expression has been found in a variety of human malignancies including B-cell leukemias and lymphomas. The purpose of this study is to determine the miRNA expression patterns in DLBCL and their relationship with clinical characteristics and outcome. We used high throughput quantitative RT-PCR technology (Taqman Low density Arrays) to analyze the expression profile of 365 different mature miRNA in 12 Diffuse Large B-Cell Lymphoma (DLBCL) samples which had been previously characterized at the transcriptional level with Affymetrix HU133A micro-arrays. MiR-155 expression was significantly lower in the 6 samples with a Germinal Center (GC) mRNA profile than in the 6 samples with an Activated B-Cell (ABC) profile. Expression of miR-155 and of different miRNA involved in lymphoid differentiation (miR-181a, miR127) or tumour pathogenesis (cluster miR 17–92) were further evaluated in a series of 64 patients with DLBCL treated with Rituximab associated with chemotherapy (R-CHOP). 28 patients had been enrolled in the LNH98.5 GELA trial between February 1998 and February 2000 and 36 were treated with R-CHOP in GELA centers after the closure of the LNH98-5 trial, between November 2000 and June 2004. The median follow up of these patients is 69 months. Patients median age at diagnosis was 69 years (range 59–82) and 28 patients presented with an International Prognostic Index (IPI) score of more than 3. Mature miRNA expression was determined by quantitative RT-PCR with Applied Biosystems specific miRNA primer and probe sets and normalized to U6 small nuclear RNA expression. MiR-155 expression was significantly higher in patients with a lymphoma of the ABC subtype, defined on the basis of the transcriptional profile (mean delta Ct = − 3.9 in the 41 ABC samples, mean delta Ct = − 1.67 in the 23 GC samples, p<0.00001) and significantly higher in patients with a high (4 or 5) IPI score (p=0.02). A high miR-155 expression was associated with a trend towards a poorer overall survival. The expression of miR-127, miR-181a and the cluster 17–92 were not correlated with clinical outcome. These analyses are currently being extended to a larger series of patients in order to determine whether other miRNA can be used to classify DLBCL samples into ABC and GC subtypes and whether some miRNA have prognostic significance in the era of treatments combining Rituximab and chemotherapy.