Sensitivity of primary T-ALL from relapsed patients to L-alanosine. Primary T-ALL cells from relapsed patients were treated with increasing concentrations of L-alanosine for 3 days. Control cells were cultured in media alone. Cells were then pulsed with ³H-thymidine for 6 hours and incorporation of ³H-thymidine was determined in a scintillation counter. MTAP status was determined by PCR and/or Western blot analysis. Horizontal line separates primary T-ALL cells that are resistant to the cytotoxicity of L-alanosine (IC₅₀ ≥ 80 μM) from those that are sensitive.