AIN:To search for the biomarker of cellular immortalization,the telomere length,telomerase activity and its subunits incultured epithelial cells of human fetal esophagus in theprocess of immortalization.METHODS:The transgenic cell line of human fetalesophageal epithelium(SHEE)was established with E_6E_7genes of human papillomavirus(HPV)type 18 in ourlaboratory.Morphological phenotype of cultured SHEE cellsfrom the 6th to 30th passages,was examined by phasecontrast microscopy,the telomere,length was assayed bySouthern blot method,and the activity of telomerase wasanalyzed by telomeric repeat amplification protocol(TRAP).Expressions of subunits of.telomerase,hTR and hTERT,were assessed by RT-PCR.DNA content in cell cycle wasdetected by flow cytometry.The cell apoptosis wasexamined by electron microscopy(EM)and TUNEL label.RESULTS:SHEE cells from the 6 th to l0 th passagesshowed cellular proliferation with a good differentiation.From the 12 th to the 16 th passages,many senescent andapoptotic cells appeared,and the telomere length sharplyshortened from 23 kb to 17 kb without expression of hTERTand telomerase activity.At the 20 th passage,SHEE cellsovercame the senescence and apoptosis and restored theirproliferative activity with expression of telomerase andhTERT at low levels,but the telomere length shortenedcontinuously to the lowest of 3 kb.After the 30 th passagecells proliferation was restored by increment of cells at S andG2M phase in the cell cycle and telornerase activity expressedat high levels and with maintenance of telomere length.CONCLUSION: At the early stage of SHEE cells, telomeres are shortened without expression of telomerase and hTERT causing cellular senescence and cell death. From the 20 th to the 30 th passages, the activation of telomerase and maintenance of telomere length show a progressive process for immortalization of esophageal epithelial cells. The expression of telomerase may constitute a biomarker for detection of immortalization of cells. AIN: To search for the biomarker of cellular immortalization, the telomere length, telomerase activity and its subunits incultured epithelial cells of human fetal esophagus in the process of immortalization. METHODS: The transgenic cell line of human fetalesophageal epithelium (SHEE) was established with E_6E_7genes of Human papillomavirus (HPV) type 18 in our laboratory. Morphological phenotype of cultured SHEE cells from the 6th to 30th passages, was examined by phasecontrast microscopy, the telomere, length was assayed by Southern blot method, and the activity of telomerase wasanalyzed by telomeric repeat amplification protocol ( TRAP). Expressions of subunits of. Telomerase, hTR and hTERT, were were by RT-PCR. DNA content in cell cycle wasdetected by flow cytometry. Cell apoptosis wasexamined by electron microscopy (EM) and TUNEL label.RESULTS: SHEE cells from the 6 th to l0 th passagesshowed cellular proliferation with a good differentiation. From the 12 th to the 16 th passages, many senescent andapopt otic cells, and the telomere length sharply deleted from 23 kb to 17 kb without expression of hTERT and telomerase activity. At the 20th passage, SHEE cell sovercame the senescence and apoptosis and restored their profoliferative activity with expression of telomerase and hTERT at low levels, but the telomere length shortenedcontinuously to the lowest of 3 kb. After the 30th passagecells proliferation was restored by increment of cells at S and G2ERM phase in the cell cycle and telornerase activity expressedat high levels and with maintenance of telomere length. CONCLUSION: At the early stage of SHEE cells, telomeres are shortened without expression of telomerase and hTERT causing cellular senescence and cell death. From the 20th th to the 30 th passages, the activation of telomerase and maintenance of telomere length show a progressive process for immortalization of esophageal epithelial cells. The expression of telomerase may constitute a biomarker for detection of immortalization of cells.