ALK and anaplastic large cell lymphoma: Using a Sox2 reporter containing the SRR2 (Sox2 Regulatory Region-2) sequence, we previously identified the existence of two phenotypically distinct cell subpopulations in ALK + ALCL cell lines, with a small subset of cells being Sox2active (currently denoted as Reporter Responsive, RR) and the majority of the cells being Sox2inactive (denoted as reporter unresponsive, RU) [10].