Relationship Between Immunophenotyping and X-inactive Specific Transcript (Xist) Gene in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous disorder characterized by clonal expansion of myeloid progenitors (blasts) in the bone marrow and peripheral blood. with high mortality and variable prognosis. AML is the most common acute leukemia in adults, accounting for ~ 80 percent of cases in this group. There are approximately 19,520 new cases of AML in the United States (US) each year and 10,670 deaths from AML. In Egypt, the incidence of AML was 0.96% for males and 1.14% for females according to the results of the National Population-Based Registry Program of Egypt (2008-2011). Diagnosis of AML based on morphological diagnosis with proliferation of blast cells ≥ 20% of marrow cells, flow cytomtric immunophenotyping and cytogenetic abnormalities.

Immunophenotyping via flow cytometry comprises an additional fast technique to predict outcome in AML, although only few markers are yet established as prognostic factors in clinical routine diagnosis, despite the fact that new and rapidly available markers are needed to improve the treatment decisions in AML patients. This is even more since therapy in AML patients must be initiated immediately after diagnosis. AML blasts express antigens found also on healthy immature myeloid cells, including common differentiation (CD) markers CD13, CD33 and CD34. Other cells markers are expressed depending on the morphological subtype of AML and stage of differentiation block such as monocytic differentiation markers (CD4, CD14, CD11b, CD11c, CD64, CD36), erythroid (CD36, CD71) and megakaryocytic markers (CD41a and CD61).

Non-random chromosomal abnormalities (e.g., deletions, translocations) are identified in approximately 52% of all adult primary AML patients and have long been recognized as the genetic events that cause and promote this disease. Certain cytogenetic abnormalities, including the t(8;21)(q22;q22), t(15;17)(q22;q12) and inv(16)(p13.1;q22) are associated with longer remission and survival, while alterations of chromosomes 5, 7, complex karyotype (described as >3 chromosomal abnormalities) and 11q23 are associated with poor response to therapy and shorter overall survival.

Several studies have reported correlations of aberrantly expressed markers with clinical outcome in AML. For example, CD7 and CD25 expression has been associated with poor prognosis in normal karyotype (NK) AML. The IL3 receptor alfa (CD123) is overexpressed in 45% of AML patients, and this higher expression has also been associated with poor outcome and correlated with mutations in the fms-like tyrosine kinase receptor (FLT3) gene. A consistent antigenic profile with high CD33 expression has also been associated with AML with mutated nucleophosmin (NPM1). Lo-Coco et al., (2015) results suggest that the CD34/25/123/99+ve leukemia-associated immunophenotypes (LAIPs) is strictly associated with FLT3-ITD positive cells. This identification through multiparametric flow cytometry at diagnosis of an immunophenotypic fingerprint associated with these subclones is a novel and simplified tool with improved sensitivity to unravel these clones and allowing patient stratification and risk adapted treatment with potential impact on outcome of the disease.

At present, the etiological agent and pathogenesis of AML are not entirely clear, only few AML cases can be accurately classified through traditional cellular morphological classification. Thus, it is very difficult to judge the disease condition and predict prognosis. Improper expression of specific genes is a common finding in AML and may induce clinically relevant biological subsets. Consequently, identification of novel biomarkers which could predict outcome or guide treatment choice will make more contribution to the clinical management of AML.