G6PD and fibrosarcoma: As shown in Figure 1, G418-resistant cells from pBABE-Puro-hTERT-transfected normal and G6PD-deficient fibroblasts expressed similarly high telomerase activity that was comparable to that of a telomerase-positive fibrosarcoma cancer cell line (HT1080), whereas no telomerase activity was detected in G418-resistant cells transfected with the pBABE-Puro vector.