Association of acute myeloid leukemia's most immature phenotype with risk groups and outcomes

Abstract

The precise phenotype and biology of acute myeloid leukemia stem cells remain controversial, in part because the "gold standard" immunodeficient mouse engraftment assay fails in a significant fraction of patients and identifies multiple cell-types in others. We sought to analyze the clinical utility of a novel assay for putative leukemia stem cells in a large prospective cohort. The leukemic clone's most primitive hematopoietic cellular phenotype was prospectively identified in 109 newly-diagnosed acute myeloid leukemia patients, and analyzed against clinical risk groups and outcomes. Most (80/109) patients harbored CD34(+)CD38(-) leukemia cells. The CD34(+)CD38(-) leukemia cells in 47 of the 80 patients displayed intermediate aldehyde dehydrogenase expression, while normal CD34(+)CD38(-) hematopoietic stem cells expressed high levels of aldehyde dehydrogenase. In the other 33/80 patients, the CD34(+)CD38(-) leukemia cells exhibited high aldehyde dehydrogenase activity, and most (28/33, 85%) harbored poor-risk cytogenetics or FMS-like tyrosine kinase 3 internal tandem translocations. No CD34(+) leukemia cells could be detected in 28/109 patients, including 14/21 patients with nucleophosmin-1 mutations and 6/7 acute promyelocytic leukemia patients. The patients with CD34(+)CD38(-) leukemia cells with high aldehyde dehydrogenase activity manifested a significantly lower complete remission rate, as well as poorer event-free and overall survivals. The leukemic clone's most immature phenotype was heterogeneous with respect to CD34, CD38, and ALDH expression, but correlated with acute myeloid leukemia risk groups and outcomes. The strong clinical correlations suggest that the most immature phenotype detectable in the leukemia might serve as a biomarker for "clinically-relevant" leukemia stem cells. ClinicalTrials.gov: NCT01349972.

Copyright© Ferrata Storti Foundation.

Figures

Figure 1.

Assessment of CD34+ cells from an NPM1 and FLT3-ITD mutated AML patient with < 1% CD34+ cells. (A) Representative flow cytometric staining pattern of ALDH activity by CD34 is displayed on MMNCs from patient. All the CD34+ cells are CD34+CD38−ALDHhigh. The CD34+ALDHhigh cells are shown in rectangle. (B) FLT3-ITD status of isolated cell fractions. The CD34−blasts harbored the FLT3-ITD mutation, while the CD34+ cells exclusively displayed the 330bp wild-type gene.

Figure 2.

Prominent ALDHint population of CD34+CD38− cells from a patient with FLT3-ITD AML. (A) Representative flow cytometric staining pattern of ALDH activity by side scatter (SSC) is displayed for CD34+CD38− cells isolated from patient. (B) FLT3-ITD status of isolated cell fractions. The CD34+CD38−ALDHint population (oval) harbored the FLT3-ITD mutation, while the CD34+CD38−ALDHhigh cells (square) exclusively displayed the 330bp wild-type gene.

Figure 3.

Prominent ALDHhigh populations of CD34+CD38− cells. (A) Representative flow cytometric staining pattern of ALDH activity by side scatter (SSC) is displayed for CD34+CD38− cells isolated from patient. The CD34+CD38−ALDHhigh cells represented essentially all of the total CD34+CD38− cells. (B) FLT3-ITD status of isolated cell fractions. The CD34+CD38−ALDHhigh population harbored the FLT3-ITD mutation. (C) Representative flow cytometric staining pattern of ALDH activity by side scatter (SSC) is displayed for CD34+CD38− cells isolated from a patient with dual CD34+CD38−ALDHint and CD34+CD38−ALDHhigh populations.

Figure 4.

(A) OS and (B) EFS in clinical trial NCT01349972 by the most immature phenotype detectable in leukemia cells. With a median followup of 22 (range 12–36) months, OS (P=0.02) and EFS (P<0.001) were significantly different according to the leukemias’ most primitive hematopoietic phenotype.