Flow Cytometry:T-Lymphoid lineage assignment

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Requirements to assign T-lymphoid lineage For T-lymphoid lineage assignment the key lineage-marker is CD3. Provided that this marker meets the intensity criteria then it is T-lineage defining in MPAL. This expression can be determined either by CD3 detection by flow cytometry OR by immunocytochemistry on trephine.
Marker requirement
Either CD3 surface or cytoplasm (strong) Or CD3 by immunocytochemistry (strong)	To meet the definition of "strong" the expression intensity must exceed that of 50% of normal T lymphocytes

Notes on interpretation of T-lineage in MPAL
Expression of CD3 is required to assign T lineage in MPAL. Generally, other T-associated antigens will also be expressed:.CD7, and in the majority of cases. CD2, CD4, CD5, and CD8. Consider also that a proportion of early T precursor lymphoblastic leukaemia/lymphoma (ETP-ALL) may be difficult to distinguish from MPAL-T/M. Using an appropriate threshold for MPO positivity may be helpful and a threshold of >10% for myeloperoxidase positivity is broadly advised by WHO in this context.

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