Quantification of ZAP-70 expression in chronic lymphocytic leukemia: T/B-cell ratio of mean fluorescence intensity provides stronger prognostic value than percentage of positive cells.

February 8, 2011

BlankQuantification of ZAP-70 expression in chronic lymphocytic leukemia:

T/B-cell ratio of mean fluorescence intensity provides stronger prognostic value

than percentage of positive cells.

L Smolej, V Vroblova, M Motyckova, K Jankovicova, D Schmitzova, J Krejsek, and J

Maly

Neoplasma, January 1, 2011; 58(2): 140-5.

Expression of ZAP-70 measured by flow cytometry belongs to the most powerful

prognostic parameters in chronic lymphocytic leukemia (CLL). However, many

technical factors such as setting of the positivity threshold may significantly

influence results.. Quantification using mean fluorescent intensity (MFI) may

eliminate the subjective error which is inevitable in the isotype control

method. The aim of the present project was therefore to assess the prognostic

significance of ZAP-70 using three different methods. Between 2005 and 2010 we

measured ZAP-70 expression in 157 patients with CLL (108 males, 49 females,

median age 60 years [range, 31-82]; low/intermediate/high Rai risk in

41/48/11%). Expression of ZAP-70 was determined by flow cytometry using

phycoerythrin (PE)-conjugated monoclonal antibody, clone 1E7.2. <br />Evaluation

was performed by 1) percentage of positive cells compared to isotype control

(cut-off 20%), 2) MFI ratio of T-cells/CLL cells (cut-off 3.0); 3) MFI ratio of

ZAP-70/isotype control on CLL cells (cut-off 2.5). MFI method with T-cells/CLL

cells ratio was the best in the identification of patients with unfavourable

outcome: ZAP-70 positive patients had significantly shorter time to treatment

(TTT, median 24 vs. 55 months, p=0.0001) and overall survival (OS, median 97 vs

174 months, p=0.0074). The differences in TTT a OS were not significant with the

use of isotype percentage and MFI isotype methods. Combined analysis of ZAP-70

with CD38 expression or IgVH mutation status lead to identification of a

subgroup with the longest TTT and OS (ZAP-70 and CD38 negative, p<0.0001 and

p=0.012; ZAP-70 negative and mutated IgVH genes, p<0.0001 and p=0.0019).<br />In

conclusion, our results suggest that measurement of ZAP-70 expression in CLL by

MFI using T-cells/CLL cells ratio might be the optimal method for accurate

prediction of clinical course. Combined analysis of ZAP-70 with CD38 or IgVH

mutation status further refined individual patient?s prognosis. Keywords:

chronic lymphocytic leukemia, ZAP-70 expression, mean fluorescence intensity,

isotype control, prognosis.

PMID: 21275464

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