To understand if the aggressive murine leukemia in Eμ-MTCP1 transgenic mice were composed of heterogeneous, polyclonal B cells or derived from a single precursor founding a homogeneous tumor population as is the case in human CLL, we evaluated the B-cell receptor (BCR) repertoire by examining IGH transcripts via RNA-sequencing methods previously described by our group36. Here, BCR is linked to B-cell chronic lymphocytic leukemia.