Immature CD34+CD19- progenitor/stem cells in TEL/AML1-positive acute lymphoblastic leukemia are genetically and functionally normal

One important question in stem cell biology of childhood acute lymphoblastic leukemia (ALL) is whether immature CD34(+)CD19(-) cells are part of the leukemic cell clone. CD34(+)CD19(-) cells from the bone marrow of 9 children with TEL/AML1-positive ALL were purified by flow sorting and subjected to reverse transcriptase-polymerase chain reaction (RTPCR), fluorescence in situ hybridization, and methylcellulose cultures. In 3 of 8 patients analyzed by RT-PCR, no TEL/AML1-positive cells could be detected in the CD34(+)CD19(-) cell fraction. Altogether, the percentage of TEL/AML1-positive cells was low: 1.6% (n = 8; SD 2.2%) by nested real-time RT-PCR and 2.5% (n = 5; SD 2.6%) by fluorescence in situ hybridization. This correlated with the percentage of contaminating CD19(+) leukemic cells in the CD34(+)CD19(-) cell fraction in 6 control sorts (mean 4.6%, SD 3.6%), indicating that the low levels of leukemic cells detected in the CD34(+)CD19(-) cell fraction could be attributed to sorter errors. Methylcellulose cultures in 3 patients provided further evidence that CD34(+)CD19(-) cells represent a candidate normal cell population. The clonogenicity of the CD34(+)CD19(-) cell fraction was similar to normal progenitors, including growth of primitive granulocyte, erythroid, macro- phage, megakaryocyte colony-forming units. Each of 92 colonies from cultures with CD34(+)CD19(-) cells tested negative for TEL/AML1. In conclusion, our data support the hypothesis that the leukemia In TEL/AML1-positive childhood ALL originates in a CD19(+) lymphoid progenitor. This has many therapeutic Implications, eg, for purging of autologous stem cell products, flow cytometric monitoring of minimal residual disease, and targeting immunotherapy against the leukemic cell clone. (C) 2002 by The American Society of Hematology.