MicroRNAs Specific for Immune-Privileged Diffuse Large B-Cell Lymphoma.

Introduction Primary diffuse large B-cell lymphomas (DLBCL) constitute a heterogeneous group of tumors with a great diversity in both clinical presentation and outcome. Besides nodal DLBCL, about 40% of these tumors present in different extranodal sites, both immune privileged sites such as the testis and the central nervous system (PCNSL) but also non immune privileged sites such as bone, stomach, skin and mediastinum. Remarkably each of these sites show a marked divergence in biological behavior. Recent studies have shown that certain non-coding short RNAs (22nt) called miRNAs may play a role in the pathogenesis of DLBCL. These miRNAs posttrancriptionally down regulate expression of genes. Aim of study To examine the expression levels of selected miRNAs in different DLBCL sites.

Methods and Materials 51 cases of Ann Abour stage I and II primary DLBCL were divided into 4 groups; 19 nodal cases, 11 non-immune privileged site-associated (non-IP) extranodal cases, 9 PCNSL, and 12 testicular DLBCL. Each case was classified GCB or non-GCB using the algorithm as described by Hans et al. 13 miRNAs were selected from current literature on the basis of their involvement in B-cell lymphoma (miR-15, -16, -21, -221, -155, - 181a, -18a, -19, -20a, 17-3p, -17-5p and -92). The expression levels of the mature microRNAs were determined by qRT-PCR using Taqman miRNA assays. Results were compared by using 2^−ΔCt and 2^−ΔΔCt. Differences in expression levels between the four groups was tested using ANOVA.

Results Of the selected microRNAs, miR-127, miR-17-5p and miR-221 show a significant difference in expression level between the immune privileged site-associated DLBCL (IP-DLBCL) and nodal DLBCL. Both miR-17-5p (p=0.0003) and miR-221 (p=0.0032) show an increased expression level in PCNSL compared to nodal DLBCL and miR-127 shows a significant increased level in testicular DLBCL compared to nodal (p=0.0011) and non-IP (p=0.0393) DLBCL. Also of interest is the fact that miR-17-5p and miR-127 show a significant difference in the level of expression between both PCNSL and testicular DLBCL. MiR-155 shows no significant difference in expression levels between nodal and extranodal DLBCL. Analysis on the basis of GCB and non-GCB classification is currently being undertaken.

Conclusion In PCNSL miR-17-5p and miR-221 are specifically increased whereas miR-127 shows a specifically higher expression in testicular DLBCL when compared to non-IP and nodal DLBCL. Also PCNSL and testicular DLBCL differ in expression of miR-17-5p and miR-127. In contrast to previous reports miR-155 does not show any significant difference between nodal and extranodal groups. This may be caused by the selection of stage I or II primary DLBCL in contrast to previous publications which used a more heterogeneous group of DLBCL.