Very Late Antigen-4 (VLA-4) Expression by AML Blasts: Correlation of VCAM-1 Binding to Overall Survival

• Published in: Blood 2005-11, Vol.106 (11), p.2365-2365
• Main Authors: Becker, Pamela S., Papayannopoulou, Thalia, Kopecky, Kenneth J., Hanks, Adrianne N., Harlan, John M., Willman, Cheryl L., Appelbaum, Frederick R.
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V106.11.2365.2365

Adhesion of acute myeloid leukemia (AML) blasts in the bone marrow (BM) microenvironment is known to protect the cells from chemotherapy-induced apoptosis. Understanding the mechanisms of blast cell adhesion and adhesion-mediated chemotherapy resistance may be critical to improving response to chemotherapy. One study in AML patients (pts) proposed that expression of the adhesion receptor, VLA-4, is associated with chemotherapy resistance, leading to reduced survival (Matsunaga et al. 2003). VLA-4, composed of α4 and β1, binds to both the CS-1 domain of fibronectin (Fn) and vascular cell adhesion molecule-1 (VCAM-1), and has a major role in retaining stem/progenitor cells within the BM. We examined frozen BM samples from 175 AML pts (age 18–80, median 48) who underwent induction chemotherapy with anthracycline and cytarabine on Southwest Oncology Group clinical trials. Thawed samples were incubated in serum containing media with IL-3 and SCF for 16h prior to analysis. To assess the effect of freezing and thawing, we examined VLA-4 expression by cell lines and fresh versus frozen AML BM samples treated similarly, and found no difference in % expression. Flow cytometry was performed with gating on blasts by both forward vs. side scatter and CD45 vs. side scatter, and on viable cells by exclusion of 7-AAD. Both % positive cells and mean fluorescence intensity were measured. VLA-4 expression varied widely, with mean expression 60.6% (range 6.2–99.6%) for α4. VLA-4 functional adhesion was also measured. An in vitro cell adhesion assay to Fn peptide CH-296, performed on 20 randomly selected samples, revealed that pts with low α4 expression (