Low Epression of MiR-18a Distinguishes Pediatric and Adult Acute Lymphoblastic Leukemia from Each Other

In several adult solid cancers the presence or absence of an inflammatory microenvironment has turned out to be an important prognostic factor. Acute lymphoblastic leukemia (ALL) is seen in both adults and children but the response to chemotherapy and survival is significantly worse in adults than children. Therefore, we wanted to study whether the expression of immune system associated molecular markers would be different in adult and pediatric ALL patients at the time of diagnosis. IDO and FOXP3 were studied from paraffin embedded tissue samples by immunohistochemistry in 12 pediatric and 10 adult bone marrow samples. Inflammation associated miRNA analysis were performed in 19 adult and 79 pediatric ALL patients and involved miR-10, miR-15, miR-16, miR-17-92 cluster, miR-33, miR-146a, miR-150, miR-155, miR-181a, miR-222, miR-223, and miR-339. miRNAs were first analysed by Agilent's miRNA microarray and thereafter validated by qRT-PCR. miRNAs not expressed in at least 75% of one group of samples were excluded. Significance (p <0.05; q<0.1) of differential expression was estimated by t-test for those miRNAs with at least a 2.0 fold change. Sufficient RNA for qRT-PCR was available for 42 pediatric and 19 adult patients. The adult and pediatric ALL patients had quantitatively and qualitatively similar expression of IDO and FOXP3 in leukemic bone marrow samples (p=0.26 and 0.74, respectively). Out of studied miRNAs only miR-18a differed significantly in microarray analysis between adult and pediatric ALL being lower in children (FC -3.74; p 0,0037). Results were confirmed by qRT-PCR (upregulated in adults, FC 3.71, p 0.003161). The other members of the miR-17-92 cluster did not differ significantly. We conclude that pediatric and adult ALL patients have remarkably similar pattern of immune cell associated markers in bone marrow at diagnosis. This is in line with recent evidence that the outcome of the adult ALL patients can be significantly improved if treated with pediatric protocols. However, the low expression of miR-18a in pediatric ALL is interesting and demands further studies.