CD5

Summary

This marker is expressed by normal T cells and a subset of normal B cells, however it main diagnostic role is in diagnosis of certain B cell disorders:

• In mature B cell neoplasms CD5 is used to indicate likely CLL or MCL (both have consistent expression of CD5)

• In acute lymphoblastic leukaemia CD5 is useful to indicate T lineage, with (relatively) low levels of aberrant expression

• It has low frequency of expression on other lymphoma types.

Normal expression and function

CD5 binds to the B-cell ligand CD72, and has a negative effect on T and B cell receptor signalling raising the threshold for response to antigen (possibly limiting responses to self-antigens). It is a pan T cell antigen (present on thymocytes and mature T cells) that is also expressed on a subset of B cells (B1 subset comprising around 10% of adult B cells, but with a wide range according to age and disease state). CD5 is expressed at higher level on T cells than B cells, and expression is increased on activation.

Diagnostic role

• CD5 is expressed by almost all cases of CLL/SLL and the majority of cases of mantle cell lymphoma (90%)

• However, CD5 can be expressed by marginal zone lymphoma (15%); lymphoplasmacytoid lymphoma (5-10%); and occasionally diffuse large B cell lymphomas (10%) (where it may be associated with poorer prognosis and Activated B Cell (ABC) subtype).

• CD5 is expressed by most mature T cell neoplasms (with the exception of hepatosplenic T Cell lymphoma and T cell large granular lymphocytic leukaemia).

• CD5 is useful in the diagnosis and classification of T cell acute lymphoblastic leukaemia (T-ALL) since it is positive in 90% of T-ALL, although expression may be dim or absent in early precursor T ALL.

Other relevant information:

Aberrant expression of CD5 by B-ALL (rare) or AML (around 10%) is described, but in both cases CD5 expression appears less common compared with other “ambiguous markers”.

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SUMMARY TABLES

Expression in primitive cell types
AML	B ALL	Burkitt	T ALL	ETP ALL (i)	MPAL i	Hgns i
5-20%	<5%	<5%	40-80%	20-40% DIM	? <5% 5-20% 20-40% 40-80% 80-100%	20-40%

Notes: xxxxx

Expression in mature B cell neoplasms
CLL	MCL	FL	MZL	HCL	DLBCL	LPL	PCL
? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%

Notes: xxxxx

Expression in mature T cell neoplasms*
ATLL	CTCL/Sezary	T-PLL	T-LGL	NK-LGL
? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%

Notes: xxxxx

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SUMMARY TABLES

Expression by acute leukaemias and by haematogones

• Rare.png

  Pro-B ALL

• Rare.png

  Early pre-B ALL

• Rare.png

  Pre-B ALL

• Rare.png

  Early B ALL

• Hi.png

  Pro-T ALL *

• Hi.png

  Mature-T ALL

• Poss.png

  AML

• Poss.png

  Haemato-gones *

* May be present on late haematogones * Weak CD5 is seen in early precursor T-ALL

Expression by B-lymphoproliferative disorders

• Hi.png

  CLL

• Freq.png

  PLL

• Hi.png

  MCL

• Rare.png

  FL

• Poss.png

  HCL

• Poss.png

  HCLv

• Poss.png

  MZL

• Rare.png

  LPL

• Rare.png

  PCs

* occasionally described in FL

Expression by mature T-cell disorders

• Hi.png

  T-PLL

• Hi.png

  T-LGL

• Rare.png

  NK-LGL

• Hi.png

  ATLL *

• Hi.png

  Sezary *

• Freq.png

  Others **

* expression may be dim

** a range of other T cell disorders may circulate occasionally, marker expression varies

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