Immunophenotypic evolution of blast populations in pediatric acute myeloid leukemia

DOI: 10.1590/S1679-45082016AI3516 Acute myeloid leukemia (AML) results from accumulation of abnormal blasts in the bone marrow, interfering with hematopoiesis.(1) Multiparametric flow cytometry is an important and well-known tool for AML diagnosis and for monitoring of minimal residual disease.(2) However, this technique is still poorly explored to elucidate clonal evolution of the leukemia. We present laboratory observations of a pediatric AML case whose multiparametric flow cytometry data provided evidences of clonal history of leukemia from the diagnosis through relapses episodes. Figure 1. Multiparametric flow cytometry immunophenotyping reveals the diversity of blast subpopulation in acute myeloid leukemia. (A and B) Blast cells were gated according to the low expression of CD45 and high expression of CD34 (red population). Lymphocytes (blue population), monocytes (aqua population) and granulocytes (orange population) were also gated. (C) Multi parametric flow cytometry showed the presence of three different subpopulations of CD7-positive blasts in the first relapse: one CD19-negative and two distinct CD19-positive. (D) Detection of two subpopulations of blasts at the second relapse: CD7+/CD56+ and CD7-/CD56-. (E) Multi parametric flow cytometry showed the presence of only CD19+/CD7+/CD56+/CD3+ blasts. The analysis was performed using the Infinicyt software (Cytognos, Salamanca, Spain) Figure 2. Scheme of clonal evolution and relatedness among populations in the acute myeloid leukemia inferred from immunophenotyping data. The patients were diagnosed with two populations of blasts (gray and blue), which we supposed derived from a common founder clone. At the first relapse, we detected three different subpopulations of blasts. Beside the persistent population, that expanded in frequency (blue), the other two populations presented CD19 and most likely originated from the blue population considering the expression of CD7. At the second relapse, the CD19-positive population (orange) persisted and derived a new subclone lacking CD7 and CD56. The treatment approaches seemed to be efficient to extinct the blue and pink populations. In the last relapse, we observe two subpopulations of blasts. According to the levels of CD19 expression, and the presence of CD7 and CD56, these clones derived from the persistent CD19low and CD19high populations previously observed. The colors of the lines and boxes illustrate the different subclones identified in the course of the disease. The size of the boxes indicates the frequency of these populations in each stage. The new (additional or lacked) markers that characterized the next generation of leukemic clones are highlighted with the same color of the population line. The dotted line indicates the hypothetical presence of the population. The end of the lines indicates the extinction of that population in the history of the disease A