BACKGROUND: CD49d (a.k.a. alpha 4 integrin) plays a critical role in leukocyte trafficking, activation, survival, and facilitates interactions between leukocytes and stromal cells via VCAM-1 and fibronectin. We and others have previously reported that CD49d gene expression in CLL B-cells correlates with CD38 expression (

Durig Blood 101:2748
;
Pittner Leukemia 19:2264
). We have also confirmed CD49d protein expression correlates with CD38 protein expression on CLL B cells (Pittner Leukemia 19:2264). Notably, one small study reported that CD49d expression may relate to overall survival among CLL patients independent of CD38 status (Zucchetto, Leukemia 20:523), although the relationship to other prognostic markers, such as ZAP-70 and cytogenetic abnormalities, was not evaluated.

METHODS: We measured CD49d expression by flow cytometry in 130 patients with CLL (NCI 1996 criteria), accrued to observational studies at Mayo Clinic, between 1994 – 2006. CD49d expression was measured by 2 color flow cytometry using antibodies specific for CD19 (BD Biosciences) and CD49d (BD Pharmingen). CD49d expression was compared to level of CD38 expression, ZAP-70 expression, and degree of IgVH gene mutation (all treated as continuous variables). We also evaluated the relationship between CD49d expression and time to treatment (TTT) and other prognostic parameters, using the previously published 30% threshold to classify CD49d expression (Zucchetto, Leukemia 20:523). Finally, we evaluated the relationship between CD49d expression and in vitro sensitivity to fludarabine (1 um x 24 hrs) and chlorambucil (1um x 24 hrs) in a subset of 70 patients.

RESULTS: The percent of B-cells expressing CD49d varied from 0.3 to 99.4% among the 130 patients tested (median expression= 6.1). The level of CD49d strongly correlated with the expression of ZAP-70 (r=0.34; p<0.0001) and CD38 (r=0.65; p<0.0001), as well as the degree of IgVH gene mutation (r=−0.29; p=0.006). The relationship between CD49d expression and other prognostic parameters using the previously published 30% threshold to classify CD49d expression is shown in Table 1. The median time to treatment for patients with low CD49d expression was 14.9 years compared to 5.4 years for those with high CD49d expression (p=0.008) High CD49d expression was correlated with in vitro resistance to chlorambucil (r=0.27, p=0.03) but not fludarabine (r=0.20, p=0.09).

CONCLUSION: CD49d expression varies on CLL B-cells and relates to other prognostic parameters and TTT as well as in vitro sensitivity to chlorambucil. Since CD49d facilitates interactions between CLL B-cells and stromal cells, the association of this marker with poor prognostic features and in vitro drug resistance may relate to enhanced stromal nuturing of leukemic cells with higher CD49d expression. Additional studies are needed to determine whether CD49d expression may be clinically useful as a prognostic test or to predict response to treatment in patients with CLL.

CD49D lowCD49D highP value
% ZAP70+ 33.0 75.0 <0.0001 
% IgVH unmutated 24.3 55.6 0.02 
%CD38+ 12.8 63.9 <0.0001 
FISH   <0.0001 
%with 17p- or 11q- or 6q− 9.2 25.0  
% with +12 5.8 43.8  
%with normal or 13q− 85.1 31.3  
Current Stage   0.17 
0 30.9 16.7  
I-II 67.0 77.8  
III-IV 2.1 5.6  
CD49D lowCD49D highP value
% ZAP70+ 33.0 75.0 <0.0001 
% IgVH unmutated 24.3 55.6 0.02 
%CD38+ 12.8 63.9 <0.0001 
FISH   <0.0001 
%with 17p- or 11q- or 6q− 9.2 25.0  
% with +12 5.8 43.8  
%with normal or 13q− 85.1 31.3  
Current Stage   0.17 
0 30.9 16.7  
I-II 67.0 77.8  
III-IV 2.1 5.6  
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Topics:
antibodies, b-lymphocytes, cd19 antigens, chlorambucil, chromosome abnormality, chronic b-cell leukemias, chronic lymphocytic leukemia, color, fibronectins, flow cytometry

Disclosure: No relevant conflicts of interest to declare.

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2006, The American Society of Hematology
2006
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