The use of human telomerase reverse transcriptase (hTERT)-immortalized cells in tissue engineering protocols is a potentially important application of telomere biology. Several human cell types have been created that overexpress the hTERT gene with enhanced telomerase activity, extended life span and maintained or even improved functional activities. Furthermore, some studies have employed the telomerized cells in tissue engineering protocols with very good results. However, high telomerase activity allows extensive cell proliferation that may be associated with genomic instability and risk for cell transformation. Thus, safety issues should be studied carefully before using the telomerized tissues in the clinic. Alternatively, the development of conditional or intermittent telomerase activation protocols is needed.