Differential survival of AML subpopulations in NOD/SCID mice

Leukemia-initiating cells can retrospectively be defined by tumorigenicity in immunodeficient mice and be characterized by surface markers. The latter still being discussed for acute myeloid leukemia (AML), nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice were used to evaluate long-time reconstitution and expansion of AML subpopulations.

Bone marrow cells from patients with AML were separated according to CD34 expression, aldehyde dehydrogenase (ALDH) activity, and divisional kinetics in comparison to cord blood-derived CD34(+) hematopoietic stem cells, evaluating survival and expansion in NOD/SCID mice. The AML long-term surviving capacity of subpopulations recovered from NOD/SCID mice was confirmed by ex vivo survival.

AML mononuclear cells were detected in bone marrow and spleen of NOD/SCID mice 12 weeks after transplantation. The majority of recovered cells were CD34(+) and significantly more CD34(+) cells were recovered after application of ALDH(bright) (high ALDH activity), CD34(+), or slowly dividing (PKH(bright)) than after ALDH(dim), CD34(-), or fast dividing (PKH(dim)) cell application. CD123(+), CD63(+), and CD44v7(+) cells were also more abundant after the transfer of ALDH(bright) or CD34(+) AML mononuclear cells. In the spleen, large AML cell clusters were only recovered after ALDH(bright), CD34(+), or PKH(bright) cell transfer. Importantly, in secondary long-term in vitro cultures, quite exclusively CD34(+) AML mononuclear cells survived and expanded.

Separation of ALDH(bright), CD34(+), or PKH(bright) cells enriches for AML long-term surviving capacity, which reside in the CD34(+) subpopulation, as rather exclusively CD34(+) cells survived and expanded in vivo and ex vivo. Long-term survival capacity may be supported by CD44v7 expression.