By maintaining genome integrity, controlling cell proliferation, and regulating tissue homeostasis, telomerase plays a critical role in the pathology of aging and cancer. Telomerase is composed of telomerase RNA, or telomerase RNA component (TERC), which serves as a template for telomeric DNA synthesis, and a catalytic subunit, telomerase reverse transcriptase (TERT). The canonical function of TERT is the synthesis of telomeric DNA repeats and the maintenance of telomere length. Recent studies suggest that adeno-associated virus (AAV)-expressed TERT in adult mice can increase life span and health span. Because TERT physically interacts with proteins that regulate gene expression, and because TERT's expression at high levels is associated with oncogenic transformation, its synthesis needs to be carefully regulated. Due to safety concerns, transient expression of TERT mRNA may be preferred for tissue engineering and adoptive stem cell therapy.