D: In vitro validation of peptide specificity and PDC activity: (Specific aims 1, 2, 3) Specificity of peptides: The specificity of targeting peptides will be demonstrated by incubating peptide-dye conjugates with target and controls cells. For the mouse CLL system, A20 cells will be used as target cells and normal mouse splenic lymphocytes and primary cultures of mouse skin and epithelial cells will be used as controls cells. For the human CLL system, patient CLL cells and normal human lymphocytes and HUVEC cells will be used as target and controls cells respectively. Cells will be incubated with FITC-labeled peptides at both 4oC and 37oC, washed and analyzed for binding and internalization respectively. Binding will be evaluated by flow cytometry and internalization by confocal microscopy.