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肿瘤坏死因子（ＴＮＦ）对机体具有一定的放射线保护作用，并能增强肿瘤的放疗效果。用可被放射线转录激活的Ｅｇｒ－１启动子与人ＴＮＦ的融合基因，构建成放射线诱导性的人ＴＮＦ双拷贝逆转录病毒载体ｐＥＴＤＣ，经包装细胞Ｐｓｉ－２和Ｃｒｉｐ的两次包装后，其病毒上清的病毒滴度达４×１０５ＣＦＵ／ｍｌ。用此病毒上清感染小鼠成纤维细胞株ＮＩＨ３Ｔ３和黑色素细胞株Ｂ１６．Ｆ１０，经Ｇ４１８抗性筛选后，得到的阳性克隆分泌ＴＮＦ量分别为２．１ｎｇ／ｍｌ和１．１ｎｇ／ｍｌ，并经ＲＴ－ＰＣＲ证实了人ＴＮＦｍＲＮＡ的表达。经２０Ｇｙ的放射线体外照射后，其ＴＮＦ表达量分别升至１３．８ｎｇ／ｍｌ和５．７ｎｇ／ｍｌ，即分别为照射前的５．６倍和４．２倍。此结果为其将来瘤体内注射该ＴＮＦ基因表达载体并辅助局部放疗的体内实验打下了基础。
Tumor necrosis factor (TNF) has a certain radiation protection effect on the body, and can enhance the radiotherapy effect of the tumor. A radiation-inducible human TNF double-copy retroviral vector pETDC was constructed using a fusion gene that can be activated by radiation transcription of the Egr-1 promoter and human TNF, and the packaging cells Psi-2 and Crip were packaged twice. The virus supernatant titer reached 4 x 105 CFU/ml. The virus supernatant was used to infect mouse fibroblast cell line NIH3T3 and melanin cell line B16. F10, screened by G418 resistance, the positive clones obtained secreted TNF amounts were 2.1 ng/ml and 1.1 ng/ml respectively, and the expression of human TNF mRNA was confirmed by RT-PCR. After irradiation with 20 Gy of X-rays, their TNF expression levels increased to 13.8 ng/ml and 5.7 ng/ml, respectively, ie 5.6-fold and 4.2-fold, respectively, before irradiation. This result lays the foundation for future in vivo tumor injections of the TNF gene expression vector and adjuvant in vivo radiotherapy.