Rac inhibition overcomes T cell-mediated resistance toward fludarabine. CLL PBMCs were cultured with or without anti-CD3/CD28 microbeads for 24 hours before subsequent treatment with 10 µM fludarabine for an additional 48 hours. CLL cell viability was measured after 3 days, using annexin V/7-AAD staining of CD5/CD19⁺ cells and flow cytometric analysis (n = 12). Data are presented as box plots.