Lymphoid-associated antigen expression by acute myeloid leukemia

Area of Science:

• Hematology
• Immunophenotyping
• Molecular Diagnostics

Background:

• Lymphoid-associated antigen (LAA) expression on blasts in acute myeloid leukemia (AML) and myeloproliferative disorders with myeloid blast crisis (MPD/MBC) is often used to diagnose acute mixed lineage leukemia (AMLL).
• Distinguishing true mixed lineage from aberrant antigen expression is critical for accurate diagnosis and treatment of myeloid malignancies.

Purpose of the Study:

• To determine the incidence of LAA expression in AML and MPD/MBC (Ly+ AML).
• To assess lymphoid differentiation at the genomic level in Ly+ AML.
• To compare features of Ly+ AML with AML and MPD/MBC lacking these antigens (Ly-AML).

Main Methods:

• Reviewed 74 AML and MPD/MBC cases for morphology, TdT reactivity, and cytochemistry.
• Performed multiparameter flow cytometry for blast immunophenotyping, identifying Ly+ AML based on CD2, CD3, CD5, CD7, CD19, or CD20 expression.
• Conducted Southern blot analysis for immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements.

Main Results:

• Sixteen of 74 cases (22%) were identified as Ly+ AML.
• T-cell markers (CD7, CD2, CD5) were expressed in 44%, 38%, and 25% of Ly+ AML cases, respectively; B-cell markers (CD19, CD20) in 13% and 6%.
• Nine Ly+ AML cases showed no Ig or TCR gene rearrangements, indicating a lack of lymphoid lineage commitment.

Conclusions:

• Expression of T-cell-associated antigens (CD2, CD5, CD7) in AML does not necessarily indicate lymphoid lineage commitment.
• These findings suggest that LAA expression alone should not lead to a diagnosis of AMLL.
• Genomic analysis is crucial for confirming lineage in ambiguous cases of myeloid leukemia.