Angioimmunoblastic T-cell Lymphoma

Question 1

What normal cell counterpart is AITL thought to be derived from?

Answer 1

• CD4+ Follicular helper T cells

Question 2

What is the immunophenotype of AITL?

Answer 2

• Positive: CD2, CD5, CD4, CD10 (may be expressed only in a subset of cells)
• Note: CD10 expression may not be seen in the bone marrow.
• Negative: typically for CD3 and CD7 (both could be only partially lost)

Question 3

What markers by IHC may be more robustly positive in the neoplastic T cells when compared to CD10 by FC?

Answer 3

• BCL6 and PD-1

Question 4

What are some things to remember about CD10 expression?

Answer 4

• uncommon in other T cells lymphomas, but has been described in PTCL, NOS.
• CD10+ CD4 T cells may be seen in reactive lymphoid hyperplasia, reactive T cells in B cell LPDs and in normal peripheral blood.
• IMP: in isolation, expression of CD10 by T cells is not evidence of a neoplasm.

Question 5

What are some complicating factors in identifying the neoplastic T cells in AITL?

Answer 5

• neoplastic cells may represent only a small percentage of the total cells
• CD4:CD8 ratio may be normal
• surface CD3 is often absent, so gating strategies need to remember this

Question 6

B cell clones associated with AITL may be seen how by FC?

Answer 6

• increase in CD38 bright plasma cells or immunoblasts with or without light chain restriction
• these are typically the EBV+ immunoblastic proliferations, which may eventually evolve into a B cell lymphoma