dGuo in presence of forodesine is accumulated as dGTP in CLL cells, and the accumulation decreased in presence of bone marrow stromal cell lines. CLL cells (n = 5) were incubated without or with 2μM forodesine and 20μM dGuo in suspension or on MSCs for 24 hours (A) or 48 hours (B), and the accumulation of dGTP was measured by DNA polymerase assay in treated and untreated time-matched controls. C indicates CLL; F, forodesine plus dGuo; M, M210B4; and N, NKtert.