CEM-TK(-)

CEM-TK− cells are thymidine kinase-deficient derivatives of the human CCRF-CEM lymphoblast lineage used to determine whether nucleoside and nucleotide analogues require cellular thymidine kinase activation[1-3]. CCRF-CEM cells normally express thymidine kinase involved in thymidine phosphorylation, whereas CEM-TK− cells lack sufficient activity to activate conventional nucleoside forms^[1][3]. Their differential responses have been used to evaluate intracellular monophosphate delivery: masked nucleotide prodrugs can retain activity in CEM-TK− cells, while compounds that merely release an unphosphorylated nucleoside remain inactive; the literature supports this biochemical phenotype and antiviral-prodrug application but does not specify the exact clone or selection history^[2][3].