HLA-DR antigen-negative acute myeloid leukemia.

Area of Science:

• Hematology
• Immunology
• Oncology

Background:

• Human leukocyte antigen (HLA) Class II antigens are expressed on acute myeloid leukemia (AML) blasts, but their significance is unclear.
• Understanding HLA Class II expression is crucial for AML subtyping and treatment.

Purpose of the Study:

• To characterize acute myeloid leukemia (AML) cases lacking Human Leukocyte Antigen (HLA) -DR expression.
• To investigate the clinical and biological implications of HLA-DR negativity in AML.

Main Methods:

• Immunophenotyping of 248 adult AML patients using multiparameter flow cytometry at diagnosis.
• Analysis of cytogenetic abnormalities, specifically t(15;17) in acute promyelocytic leukemia (APL) cases.
• Morphological assessment and comparison between HLA-DR-negative and HLA-DR-positive AML subtypes.

Main Results:

• 43 out of 248 AML patients (17%) lacked detectable HLA-DR expression on blasts.
• HLA-DR-negative cases comprised 20 acute promyelocytic leukemia (APL) and 23 non-APL subtypes.
• Three HLA-DR-negative non-APL cases exhibited morphology mimicking the hypogranular variant of APL.
• Treatment response was similar between HLA-DR-negative non-APL and HLA-DR-positive AML patients.
• HLA-DR expression changes at relapse were infrequent (4% loss, 17% gain).

Conclusions:

• HLA-DR-negative AML is a distinct entity including both APL and non-APL cases.
• Morphology alone is insufficient for diagnosing APL in HLA-DR-negative cases; cytogenetic or molecular confirmation is essential.
• Lack of HLA-DR expression does not significantly impact initial treatment response in non-APL AML.