Quantitative study of BAALC- and WT1-expressing cell precursors in the patients with different cytogenetic and molecular AML variants treated with Gemtuzumab ozogamicin and hematopoietic stem cell transplantation

Abstract

There is evidence that relapses of acute myeloid leukemia (AML) are closely related to heterogeneous population of leukemic precursors. At least, two classes of the leukemia-initiating cells (LIC) may be discerned, according to recent experimental studies with hematopoietic cell transplants to immunodeficient mice. The main class of LICs is presented by immature precursors with CD34 + CD38immunophenotype which, in turn, are capable of selective expression of BAALC gene. The second class of LICs is presented by relatively mature precursors with more differentiated immunophenotypes. According to indirect findings, they are able of WT1 gene expression, along with blast cells. Since both BAALC and WT1 mRNAs may be quantitatively evaluated by means of standardized quantitative polymerase reaction in real time (qRT-PCR), this approach may be effective for specifying the mechanisms of relapses and resistance to therapy in AML patients. The aim of this work was to perform simultaneous dynamic evaluation of BAALC and WT1 genes expressions along with determination of blast numbers in the tested bone marrow samples in 14 AML patients treated at our Center with Gemtuzumab ozogamicin (GO, Mylotarg), which was combined with high-dose chemotherapy (ChT), followed by allogeneic hematopoietic stem cell transplantation (allo-HSCT). Our preliminary results are as follows: a) superior 3-year overall survival (OS) in general group of patients with normal or nearly-normal karyotypes, and FLT3-mutated AML variants as compared to those with more complex karyotypes and EVI1 gene overexpression (85.7% vs 16.7%; p=0.032); b) highly sensitive response of immature BAALC-expressing precursors to combined ChT and GO treatment; c) hypothetical participation of some mature precursors, along with blast cells, in WT1 gene expression; d) real evidence for switching hematopoietic regulation from immature BAALC-expressing precursors to more mature WT1-expressing progeny. These results suggest diagnostic utility of combined BAALC/ WT1/blast counts panel for quantitative studies and assessment of distinct precursors in AML progression and emergence of relapses.

Evaluation of BAALC- and WT1-expressing leukemic cell precursors in pediatric and adult patients with EVI1-positive AML by means of quantitative real-time polymerase chain reaction (RT-qPCR)

“…Moreover, similar experiments with acute promyelocytic leukemia (APL) cells revealed more mature leukemia-initiating precursors [4 Patel et al, 2012], which, along with blast cells, according to our hypothesis, might express WT1, another pan-specific gene [5][6][7]. Since mRNA of the both genes may be detected with quantitative real-time PCR (RT-qPCR), we attempted to evaluate the genes of interest by means of this standard approach [5][6][7]. Our works have yielded the following results: a) important role of BAALC expressing stem-cells in post-transplant relapses (PTR) of AML [5][6]; b) proven clinical effect of a targeted drug (Mylotarg) upon the levels of leukemic stem cells and precursors [7]; and c) possible presence of leukemic hematopoietic regulators causing transition from some immature stem cells in AML to more mature precursors [5,7] as well as in APL [6].…”

“…In model experiments with human leukemic cells transplanted into immunodeficient mice, the earlier CD34+CD38-human stem cells were responsible for leukemia induction and, moreover, were able to express a pan-specific Brain And Acute Leukemia Cytoplasmic (BAALC) gene [2,3]. Moreover, similar experiments with acute promyelocytic leukemia (APL) cells revealed more mature leukemia-initiating precursors [4 Patel et al, 2012], which, along with blast cells, according to our hypothesis, might express WT1, another pan-specific gene [5][6][7]. Since mRNA of the both genes may be detected with quantitative real-time PCR (RT-qPCR), we attempted to evaluate the genes of interest by means of this standard approach [5][6][7].…”

“…Since mRNA of the both genes may be detected with quantitative real-time PCR (RT-qPCR), we attempted to evaluate the genes of interest by means of this standard approach [5][6][7]. Our works have yielded the following results: a) important role of BAALC expressing stem-cells in post-transplant relapses (PTR) of AML [5][6]; b) proven clinical effect of a targeted drug (Mylotarg) upon the levels of leukemic stem cells and precursors [7]; and c) possible presence of leukemic hematopoietic regulators causing transition from some immature stem cells in AML to more mature precursors [5,7] as well as in APL [6]. To support this hypothesis, we have recently studied leukemic hematopoiesis in a mixed group of adult and pediatric patients with EVI1-positive AML.…”

BAALC-Expressing Earlier Leukemic Progenitors: Crucial Role in AML Relapses with Evaluation of Their Treatment and Prevention Efficacy

“…In this case measurements of BAALC-and WT1-expressing cells were performed in 14 of specially selected AML patients treated with combination of GO, various kinds of chemotherapy as well allogeneic HSCT. As a results, we have revealed the superior 3-year overall survival (OS) rate in general group of patients with normal karyotypes, and FLT3 mutated AML variants as compared to those with more complex karyotypes and EVI1 gene overexpression (85.7% vs 16.7%; p=0.032) [20]. Hence, utility of such approach to serial studies of leukemic hematopoiesis became evident.…”