Microrna Profiling Classifies Acute Leukemias of Ambiguous Lineage As Either Acute Myeloid Leukemia or Acute Lymphoid Leukemia

Classification of acute leukemia (AL) is based on commitment of the leukemic cells to either the myeloid or the lymphoid lineage. However, a small percentage of AL cases lacks immunophenotypical lineage commitment or displays features of both hematopoietic lineages. These leukemias of ambiguous lineage represent a heterogeneous category of AL that cannot be classified as either myeloid AL (AML) or lymphoid AL (ALL). This presents a major hurdle for choice of treatment, because it is unsettled whether these patients benefit from AML or ALL treatment regimens or a mixture of both. Better diagnostic tools to define the lineage of origin for these AL would be instrumental to direct therapy decision making.

MicroRNAs are small single stranded RNA molecules which regulate gene expression by promoting degradation of mRNAs or repressing their translation. MicroRNA expression profiles have been shown to accurately discriminate AL of the lymphoid lineage from AL of the myeloid lineage. Here, we investigated microRNA expression profiles of leukemias of ambiguous lineage to classify them as either AML or ALL.

MicroRNA expression profiles of nine patients with leukemia of ambiguous lineage and eleven patients with AML, B-ALL or T-ALL were analyzed using microarray analysis. MicroRNAs differentially expressed between the myeloid and lymphoid lineage were selected using Linear Model for Microarray Analysis (LIMMA) and used for unsupervised clustering of the ambiguous lineage leukemias with the AML, B-ALL and T-ALL samples. The top five most discriminating microRNAs were selected for qRT-PCR validation in eight additional ambiguous lineage cases, five AML or ALL cases and two control cell lines.

Unsupervised clustering analysis of the AML, B-ALL and T-ALL samples resulted in a clear separation between the myeloid and lymphoid lineages. Top differentially expressed microRNAs were miR-199b, miR-27a/b, miR-223, miR-23a, miR-221 and miR-150. When comparing leukemias of ambiguous lineage with AML, B-ALL and T-ALL using LIMMA, no clear differences were found, indicating that leukemias of ambiguous lineage are not a separate entity. Moreover, unsupervised clustering of all AL samples using the top 10 percent of most variable microRNAs resulted in clustering of leukemias of ambiguous lineage with either AML, B-ALL or T-ALL and showed comparable expression profiles. Expression analysis by qRT-PCR of the five most discriminative microRNAs on the additional samples, including leukemias of ambiguous lineage, was able to accurately assign these leukemias to the lineage of origin.

MicroRNA expression profiling of leukemias of ambiguous lineage indicated the presence of a myeloid or lymphoid lineage-specific genotype despite an indistinct immunophenotype. Analyzing microRNA expression at diagnosis to classify acute leukemias of ambiguous lineage as either AML or ALL might be instrumental to therapeutic decision making.

No relevant conflicts of interest to declare.