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Acute Lymphoblastic Leukemia

 

 

 

Immunophenotype

 

Flow cytometry of the marrow aspirate sample is the technique used to phenotype the leukemic cells to allow better classification as to the type of acute leukemia.  Allows differentiation into categories of:

  • Precursor B-ALL
  • Mature B-ALL (Burkitt’s lymphoma)
  • T-ALL
  • AML (acute myelogenous leukemia)
  • Biphenotypic leukemia (blast cells show markers of more than one lineage)
  • Bilineage leukemia (two populations of blast cells exist, both with different phenotypes)

Many blasts have aberrant expression of different lineage markers (example, many pre-B ALL cases also co-express a myeloid marker) but there are specific diagnostic criteria to call a leukemia truly biphenotypic (rare).

Expression of markers parallels the cellular development through hematopoiesis from stem cell, to progenitor cells, to immature blood cells, to fully mature blood cell.

Many of these phenotypic markers are cell surface clusters of differentiation, although some are intracellular (cytoplasmic) markers.  Most are only expressed on highly immature cells.

 

Marker

Comments

Cytoplasmic TdT (Terminal Deoxynucleotide Transferase)

Found in most ALL cases but also a proportion of AML.

CD34

Common stem cell marker.  Marker of cellular immaturity.

HLA-DR

Precursor B-cell, AML (negative in M3 Acute Promyelocytic Leukemia)

CD 79a

Precursor B-cell.  Importantly, specific for B-lineage ALL.

CD22

Precursor B-cell

CD10

Precursor B-cell (called the common ALL antigen)

CD19

Precursor B-cell

CD20

Mature B-cell (seen in Burkitt’s and Burkitt’s like leukemia/lymphomas).  Target for Rituximab in more mature B-cell lymphomas.  Negative on true precursor B-ALL cases.

CD3 (cytoplasmic or cell surface)

T-ALL

CD4

T-ALL (often negative, depending on where in stage of T-cell ontogeny malignant clone developed).

CD8

T-ALL (often negative, depending on where in stage of T-cell ontogeny malignant clone developed).

CD7

T-ALL

CD1a

T-ALL

CD2

T-ALL

CD13

AML

CD14

AML

CD15

AML

CD33

AML

CD41/61 – Markers of Megakaryocytic Development

AML, Helps to differentiate M7 (Megakaryocytic Variant)

CD117

Myeloid / Stem Cell

Glycophorin A – Markers of Erythrocytic Development

AML, Helps to differentiate M6 (Erythroblastic Variant)

 

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