Effect of VEGF blockade on CLL-cell integrin clustering. CLL cells were prestained with nonblocking anti-α_L-FITC or anti-α₄-PE mAbs. After staining, cells were preincubated with the anti-VEGF blocking mAb before being placed on HUVEC monolayers, and filmed for 60 minutes using live cell imaging. The images shown were obtained after 5 minutes. In the absence of VEGF blockade, both α₄ and α_L were clearly polarized on most cells (top row), and this polarization was markedly reduced in the presence of the blocking anti-VEGF mAb (bottom row). Similar results were obtained when the SU5416 inhibitor was used to inhibit VEGF (data not shown). Comparable staining was observed throughout the 60 minutes of culture. These images are representative of 3 experiments in 3 separate patients, and the results for coclustered α₄ and α_L (composite staining) are shown quantitatively in Figure 6.