Cell of Origin Influences Leukemia Stem Cell Phenotype.

Abstract 3459

Poster Board III-347

MLL-fusion proteins can transform either hematopoietic stem cells (HSC) or granulocyte macrophage progenitors (GMP) into leukemia stem cells (LSC). However, the leukemogenic process in HSC may differ from that in GMP. We transduced HSC and GMP with MLL-AF9 or control retroviruses. Single-cell sorted MLL-AF9 expressing HSC or GMP could be serially replated for over 9 passages. Upon transplantation into syngeneic mice, 86.3% (n=22) of HSC:MLL-AF9 single cell derived clones (SCC) induced AML with a median latency of 61 days, while 33.3% of GMP:MLL-AF9 SCC induced AMLs with median latency of 100 days. Immunophenotype analysis of the resultant leukemias demonstrated that long-term repopulating HSC (LT-HSC) and GMP-derived leukemias were quite similar, with a GMP-like (LGMP) population enriched in LSC in both cases. Gene expression analysis demonstrated that globally the LGMP isolated from HSC derived AMLs (AML:HSC) and GMP derived AMLs (AML:GMP) were similar to each other but possessed specific genetic programs reminiscent of the cell of origin (HSC or GMP). For example Evi1, Jun, and Fos oncogenes were highly expressed in HSC and AML:HSC, but expressed at low level in GMP or AML:GMP. The genetic program that distinguished LGMP:HSC from LGMP:GMP was found to be enriched in hematopoietic stem cells compared to more differentiated myeloid progenitors and correlate with genetic programs in and human MLL-rearranged AML associated with a poor clinical outcome in two independent MLL-rearranged AML data sets. In order to directly assess differences in treatment response for leukemias derived from different cells of origin, we treated leukemic mice with a chemotherapeutic agent often used to treatment human AMLs. Treatment of leukemic mice with Etoposide reduced the spleen weights in mice transplanted with AML:HSC to a lesser extent (28%) than in mice transplanted with AML:GMP (88%). Altogether, these data indicate that cell of origin of AML can influence the genetic program of fully developed leukemia, and thus could account for some of the heterogeneity in human leukemias and perhaps outcome.