Immunophenotyping of acute leukemia – goals, objectives
The introduction of monoclonal antibodies into practice allowed us to identify specific receptors, antigens and other molecules (markers) on the membrane and / or in the cytoplasm of blast cells. Currently, more than 300 antigenic groups have been identified, which are called differentiation clusters (CD).
The objectives of immunophenotyping in acute leukemia:
1) confirmation of the diagnosis established on the basis of studying the morphology and cytochemistry of the blasts;
2) establishment of a diagnosis with questionable morphological and cytochemical results;
3) diagnosis of biphenotypic acute leukemia;
4) detection of aberrant antigen expression for the detection of a neoplastic clone with signs of complete remission (minimal residual disease);
5) division of acute leukemia into prognostic groups.
Cells of acute lymphoblastic leukemia of T-cell origin are characterized by the expression of T-cell markers CD2, CD5, CD7 (less commonly CD1); sometimes B-cell markers CD10 and CD21 can also be ex-compressed. In cases of B-ALL, CD19, CD10, CD22 and, depending on the stage of maturation, CD20 and surface immunoglobulin are expressed.
In acute myeloid leukemia, CD13, CD15, CD33, and CD14 are expressed (with the monocytoid component). Expression of Tdt (terminal deoxynucleotide-diltransferase) is noted in most lymphoid blasts and in 20% of cases of acute myeloblastic leukemia. CD34 can be expressed on blast cells of all lines, especially poorly differentiated.
HLA-DR is determined on B-ALL blasts, most AML (except for MV) and in rare cases with T-ALL.
In most cases of biphenotypic leukemias (a combination of phenotypes of two and even three lines), blasts show coexpression of markers of several lines; in more rare cases, the same patient simultaneously has blasts of different origin (myeloid and lymphoid) – bilinear acute leukemia.