CD10 and ICOS expression by multiparametric flow cytometry in angioimmunoblastic T-cell lymphoma

Angioimmunoblastic T-cell lymphoma is immunologically defined by the expression of CD10 and the follicular helper T cell (T-FH) markers such as CXCL13, programmed death-1 (PD-1) and inducible T-cell costimulator (ICOS). This T-FH profile has been mainly reported by immunohistochemistry. Here, using multiparametric flow cytometry, the relevance of ICOS and PD-1 to angioimmunoblastic T-cell lymphoma diagnosis was evaluated in lymph node (n = 15) as well as in peripheral blood (n = 13) among a series of 28 angioimmunoblastic T-cell lymphoma cases, in addition to the CD10 expression (available in 26 lymph node and 15 peripheral blood specimens). In this series, CD10 expression was present in 23/26 (88%) lymph node and in 12/15 (80%) peripheral blood cases and ICOS in 13/15 (87%) lymph node and in 6/13 (47%) peripheral blood cases, whereas neither significant CD10 nor ICOS T cells were identified in the control group (lymph nodes with reactive hyperplasia = 10, peripheral blood of healthy donors = 15). PD-1 expression was less informative as observed in both angioimmunoblastic T-cell lymphoma and control cases. The multiparametric approach allowed us to confirm the frequent blood dissemination in angioimmunoblastic T-cell lymphoma and to show that circulating neoplastic T cells correspond more often to a CD10-positive subset than to an ICOS-positive subset. Consequently, if ICOS constitutes an additional feature for the diagnosis of angioimmunoblastic T-cell lymphoma, it appears less sensitive than CD10 expression for the detection of circulating neoplastic T cells. Modern Pathology (2011) 24, 993-1003; doi: 10.1038/modpathol.2011.53; published online 15 April 2011