Leukemias - Biology, Cytogenetics and Molecular Markers in Diagnosis and Prognosis Poster II
The CD34+CD38LowCD19+ Candidate Leukemic Stem Cell Phenotype Revisited: Useful for Flow MRD Monitoring?
Kerrie Wilson, BSc(Hons)1,*,
Marian Case, MSc1,*,
Simon Bailey, MD, PhD, FRCPCH2,*,
Josef Vormoor, MD, FRCPCH1 and
Julie Irving, PhD1
1 Northern Institute for Cancer Research, Newcastle University, Newcastle upon Tyne, United Kingdom, 2 Royal Victoria Infirmary, Newcastle University, Newcastle upon Tyne, United Kingdom
The assessment of minimal residual disease during therapy isa powerful prognostic marker in childhood acute lymphoblasticleukemia but current techniques, whether molecular analysisof antigen receptor gene rearrangements or flow cytometric analysisof aberrant immunophenotypes, track the blast population(s)that predominate(s) at diagnosis. Recent evidence from diagnosticTEL/AML1 positive cases (Hong et al, 2008) suggests that thecandidate leukemic stem cell population may be characterisedby the immunophenotype CD34+CD38LowCD19+ and thus the identificationand quantitation of this cell population at diagnosis and duringtherapy may have greater clinical significance.
Number with candidate population
Numberwithout candidate population
Therefore, we have sought this proposed leukemic stem cell populationin 51 consecutive diagnostic precursor-B acute lymphoblasticleukaemia samples using multi-parametric flow cytometry. Patientblasts were stained with the antibodies CD34PerCP, CD38FITCand CD19APC and 50,000 events acquired on a FACSCalibur. Thepostulated cancer stem cell population, CD34+CD38LowCD19+, wasfound in 57% of patients (29 of 51). Correlation with majorcytogenetic subgroups showed that 89% (8 of 9) of TEL/AML1 positivecases had evidence of the population, compared to 55% (6 of11) of high hyperdiploid and 48% (15 of 31) of the remainder(see Table). There was no evidence of the population in normalmarrow samples which were from children in the latterstages of therapy for ALL i.e. end of treatment bone marrowsamples (n=4). We also examined bone marrow samples taken 28days after the start of treatment in a cohort of patients scoringpositive for the candidate population at diagnosis (n=11) andfound evidence for persistence of the cells in 4 of them.
CD38 under-expression, in relation to normal B cell precursors,is a common feature of ALL blasts and classification of CD38expression levels revealed that 92% (24/26) of these under-expressersunsurprisingly housed the population because their blasts werealso CD34+ and CD19+. Most importantly, since 43% of the diagnosticsamples analysed show no evidence of this population (or itexists below the limits of detection of the assay i.e.<0.1%), it seems unlikely that this represents a definitive cancerstem cell population in childhood ALL per se and would, therefore,not be appropriate as a generic marker of minimal residual leukemicstem cells.
Disclosures: No relevant conflicts of interest to declare.