ZAP-70 expression in B-cell chronic lymphocytic leukemia: Evaluation by external (isotypic) or internal (T/NK cells) controls and correlation with IgV(H) mutations

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BlankZAP-70 expression in B-cell chronic lymphocytic leukemia: Evaluation by

external (isotypic) or internal (T/NK cells) controls and correlation with

IgV(H) mutations.

Antonella Zucchetto, Riccardo Bomben, Michele Dal Bo, Paola Nanni, Pietro

Bulian, Francesca Rossi, Ilaria Del Principe, Simone Santini,

Giovanni Del Poeta, Massimo Degan, and Valter Gattei

Cytometry B Clin Cytom, August 11, 2006; 70B(4): 284-292.

Clinical and Experimental Hematology Research Unit, Centro di Riferimento

Oncologico, I.R.C.C.S., Aviano (PN), Italy.

BACKGROUND:: Expression of T cell specific zeta-associated protein 70 (ZAP-70)

by B-cell chronic lymphocytic leukemia (B-CLL) cells, as investigated by flow

cytometry, has both prognostic relevance and predictive power as surrogate for

immunoglobulin heavy chain variable region (IgV(H)) mutations, although a

standardization of the cytometric protocol is still lacking. METHODS:: Flow

cytometric analyses for ZAP-70 were performed in peripheral blood samples from

145 B-CLL (124 with IgV(H) mutations) by a standard three-color protocol.

Identification of ZAP-70(+) cell population was based on an external negative

control, i.e., the isotypic control (ISO method) or an internal positive

control, i.e., the population of residual normal T/NK cells (TNK method). A

comparison between these two approaches was performed. RESULTS:: While 86/145

cases were concordant as for ZAP-70 expression according to the two methods

(ISO(+)TNK(+) or ISO(-)TNK(-)), 59/145 cases had discordant ZAP-70 expression,

mainly (56/59) showing a ISO(+)TNK(-) profile. These latter cases express higher

levels of ZAP-70 in their normal T cell component. Moreover, discordant

ISO(+)TNK(-) cases had a IgV(H) gene mutation profile similar to that of

concordantly positive cases and different from ZAP-70 concordantly negative

B-CLL. CONCLUSION:: Analysis of ZAP-70 expression by B-CLL cells by using the

ISO method allows to overcome the variability in the expression of ZAP-70 by

residual T cells and yields a better correlation with IgV(H) gene mutations. A

receiver operating characteristic analysis suggests to employ a higher cut-off

than the commonly used 20%. A parallel evaluation of the prognostic value of

ZAP-70 expression, as determined according to the ISO and TNK methods, is still

needed. © 2006 International Society for Analytical Cytology.

PMID: 16906587