The inducible T-cell co-stimulator molecule is expressed on subsets of T cells and is a new marker of lymphomas of T follicular helper cell-derivation.
BACKGROUND
T follicular helper (T(FH)) cells reside in the light zone of germinal centers and are considered the cell of origin of angioimmunoblastic T-cell lymphoma. Recently, CXCL13, PD-1 and SAP were described as useful markers for T(FH) cells and angioimmunoblastic T-cell lymphoma but also reported in some peripheral T-cell lymphomas, not otherwise specified.


METHODS
In the present study the expression pattern of ICOS protein was investigated by immunohistochemistry-based techniques in routine sections of normal lymphoid tissues and 633 human lymphomas.


RESULTS
Cells strongly positive for ICOS were restricted to the light zone of germinal centers and co-expressed T(FH)-associated molecules. In addition, weak to moderate ICOS expression was observed in a small proportion of FOXP3-positive cells. In lymphomas, ICOS expression was confined to angioimmunoblastic T-cell lymphoma (85/86), peripheral T-cell lymphomas of follicular variant (18/18) and a proportion of peripheral T-cell lymphomas, not otherwise specified (24/56) that also expressed other T(FH)-associated molecules.


CONCLUSIONS
ICOS is a useful molecule for identifying T(FH) cells and its restricted expression to angioimmunoblastic T-cell lymphoma and a proportion of peripheral T-cell lymphomas, not otherwise specified (showing a T(FH)-like profile) suggests its inclusion in the antibody panel for diagnosing T(FH)-derived lymphomas. Our findings provide further evidence that the histological spectrum of T(FH)-derived lymphomas is broader than previously assumed.
Marafioti
Teresa
T
Leukaemia Research Immunodiagnostics Unit, Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, Oxford, OX3 9DU, UK. teresa@marafioti.org.uk
Paterson
Jennifer C
JC
Ballabio
Erica
E
Chott
Andreas
A
Natkunam
Yasodha
Y
Rodriguez-Justo
Manuel
M
Plonquet
Anne
A
Rodriguez-Pinilla
Socorro M
SM
Klapper
Wolfram
W
Hansmann
Martin-L
ML
Pileri
Stefano A
SA
Isaacson
Peter G
PG
Stein
Harald
H
Piris
Miguel A
MA
Mason
David Y
DY
Gaulard
Philippe
P
D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000378:metabolism*; D002478:Cells, Cultured; D005434:Flow Cytometry; D006801:Humans; D007119:Immunoblastic Lymphadenopathy / Q000175:diagnosis* / Q000378:metabolism; D016130:Immunophenotyping; D060889:Inducible T-Cell Co-Stimulator Protein; D008224:Lymphoma, Follicular / Q000175:diagnosis* / Q000378:metabolism; D016411:Lymphoma, T-Cell, Peripheral / Q000175:diagnosis* / Q000378:metabolism; D011379:Prognosis; D006377:T-Lymphocytes, Helper-Inducer / Q000378:metabolism*
D000945:Antigens, Differentiation, T-Lymphocyte; D014408:Biomarkers, Tumor; C556692:ICOS protein, human; D060889:Inducible T-Cell Co-Stimulator Protein